1. 13 11月, 2009 2 次提交
    • P
      rcu: Simplify association of forced quiescent states with grace periods · 8e9aa8f0
      Paul E. McKenney 提交于
      The force_quiescent_state() function also took a snapshot
      of the ->completed field, which was as obnoxious as it was in
      rcu_sched_qs() and friends.  So snapshot ->gpnum-1.
      
      Also, since the dyntick_record_completed() and
      dyntick_recall_completed() functions are now simple assignments
      that are independent of CONFIG_NO_HZ, and since their names are
      now misleading, get rid of them.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12580941042308-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      8e9aa8f0
    • P
      rcu: Accelerate callback processing on CPUs not detecting GP end · b32e9eb6
      Paul E. McKenney 提交于
      An earlier fix for a race resulted in a situation where the CPUs
      other than the CPU that detected the end of the grace period would
      not process their callbacks until the next grace period started.
      
      This means that these other CPUs would unnecessarily demand that an
      extra grace period be started.
      
      This patch eliminates this extra grace period and speeds callback
      processing by propagating rsp->completed to the rcu_node structures
      in the case where the CPU detecting the end of the grace period
      sees no reason to start a new grace period.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <1258094104417-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      b32e9eb6
  2. 11 11月, 2009 2 次提交
    • P
      rcu: Simplify association of quiescent states with grace periods · c64ac3ce
      Paul E. McKenney 提交于
      The rdp->passed_quiesc_completed fields are used to properly
      associate the recorded quiescent state with a grace period.  It
      is OK to wrongly associate a given quiescent state with a
      preceding grace period, but it is fatal to associate a given
      quiescent state with a grace period that begins after the
      quiescent state occurred.  Grace periods are numbered, and the
      following fields track them:
      
      o	->gpnum is the number of the grace period currently in
      	progress, or the number of the last grace period to
      	complete if no grace period is currently in progress.
      
      o	->completed is the number of the last grace period to
      	have completed.
      
      These two fields are equal if there is no grace period in
      progress, otherwise ->gpnum is one greater than ->completed.
      But the rdp->passed_quiesc_completed field compared against
      ->completed, and if equal, the quiescent state is presumed to
      count against the current grace period.
      
      The earlier code copied rdp->completed to
      rdp->passed_quiesc_completed, which has been made to work, but
      is error-prone.  In contrast, copying one less than rdp->gpnum
      is guaranteed safe, because rdp->gpnum is not incremented until
      after the start of the corresponding grace period. At the end of
      the grace period, when ->completed has incremented, then any
      quiescent periods recorded previously will be discarded.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12578890421011-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      c64ac3ce
    • P
      rcu: Rename dynticks_completed to completed_fqs · 4bcfe055
      Paul E. McKenney 提交于
      This field is used whether or not CONFIG_NO_HZ is set, so the
      old name of ->dynticks_completed is quite misleading.
      
      Change to ->completed_fqs, given that it the value that
      force_quiescent_state() is trying to drive the ->completed field
      away from.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12578890423298-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      4bcfe055
  3. 10 11月, 2009 3 次提交
    • P
      rcu: Fix note_new_gpnum() uses of ->gpnum · 9160306e
      Paul E. McKenney 提交于
      Impose a clear locking design on the note_new_gpnum()
      function's use of the ->gpnum counter.  This is done by updating
      rdp->gpnum only from the corresponding leaf rcu_node structure's
      rnp->gpnum field, and even then only under the protection of
      that same rcu_node structure's ->lock field.  Performance and
      scalability are maintained using a form of double-checked
      locking, and excessive spinning is avoided by use of the
      spin_trylock() function.  The use of spin_trylock() is safe due
      to the fact that CPUs who fail to acquire this lock will try
      again later. The hierarchical nature of the rcu_node data
      structure limits contention (which could be limited further if
      need be using the RCU_FANOUT kernel parameter).
      
      Without this patch, obscure but quite possible races could
      result in a quiescent state that occurred during one grace
      period to be accounted to the following grace period, causing
      this following grace period to end prematurely.  Not good!
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      Cc: <stable@kernel.org> # .32.x
      LKML-Reference: <12571987492350-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      9160306e
    • P
      rcu: Fix synchronization for rcu_process_gp_end() uses of ->completed counter · d09b62df
      Paul E. McKenney 提交于
      Impose a clear locking design on the rcu_process_gp_end()
      function's use of the ->completed counter.  This is done by
      creating a ->completed field in the rcu_node structure, which
      can safely be accessed under the protection of that structure's
      lock.  Performance and scalability are maintained by using a
      form of double-checked locking, so that rcu_process_gp_end()
      only acquires the leaf rcu_node structure's ->lock if a grace
      period has recently ended.
      
      This fix reduces rcutorture failure rate by at least two orders
      of magnitude under heavy stress with force_quiescent_state()
      being invoked artificially often.  Without this fix,
      unsynchronized access to the ->completed field can cause
      rcu_process_gp_end() to advance callbacks whose grace period has
      not yet expired.  (Bad idea!)
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      Cc: <stable@kernel.org> # .32.x
      LKML-Reference: <12571987494069-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      d09b62df
    • P
      rcu: Prepare for synchronization fixes: clean up for non-NO_HZ handling of ->completed counter · 281d150c
      Paul E. McKenney 提交于
      Impose a clear locking design on non-NO_HZ handling of the
      ->completed counter.  This increases the distance between the
      RCU and the CPU-hotplug mechanisms.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      Cc: <stable@kernel.org> # .32.x
      LKML-Reference: <12571987491353-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      281d150c
  4. 02 11月, 2009 1 次提交
    • P
      rcu: Fix long-grace-period race between forcing and initialization · 83f5b01f
      Paul E. McKenney 提交于
      Very long RCU read-side critical sections (50 milliseconds or
      so) can cause a race between force_quiescent_state() and
      rcu_start_gp() as follows on kernel builds with multi-level
      rcu_node hierarchies:
      
      1.	CPU 0 calls force_quiescent_state(), sees that there is a
      	grace period in progress, and acquires ->fsqlock.
      
      2.	CPU 1 detects the end of the grace period, and so
      	cpu_quiet_msk_finish() sets rsp->completed to rsp->gpnum.
      	This operation is carried out under the root rnp->lock,
      	but CPU 0 has not yet acquired that lock.  Note that
      	rsp->signaled is still RCU_SAVE_DYNTICK from the last
      	grace period.
      
      3.	CPU 1 calls rcu_start_gp(), but no one wants a new grace
      	period, so it drops the root rnp->lock and returns.
      
      4.	CPU 0 acquires the root rnp->lock and picks up rsp->completed
      	and rsp->signaled, then drops rnp->lock.  It then enters the
      	RCU_SAVE_DYNTICK leg of the switch statement.
      
      5.	CPU 2 invokes call_rcu(), and now needs a new grace period.
      	It calls rcu_start_gp(), which acquires the root rnp->lock, sets
      	rsp->signaled to RCU_GP_INIT (too bad that CPU 0 is already in
      	the RCU_SAVE_DYNTICK leg of the switch statement!)  and starts
      	initializing the rcu_node hierarchy.  If there are multiple
      	levels to the hierarchy, it will drop the root rnp->lock and
      	initialize the lower levels of the hierarchy.
      
      6.	CPU 0 notes that rsp->completed has not changed, which permits
              both CPU 2 and CPU 0 to try updating it concurrently.  If CPU 0's
      	update prevails, later calls to force_quiescent_state() can
      	count old quiescent states against the new grace period, which
      	can in turn result in premature ending of grace periods.
      
      	Not good.
      
      This patch adds an RCU_GP_IDLE state for rsp->signaled that is
      set initially at boot time and any time a grace period ends.
      This prevents CPU 0 from getting into the workings of
      force_quiescent_state() in step 4.  Additional locking and
      checks prevent the concurrent update of rsp->signaled in step 6.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <1256742889199-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      83f5b01f
  5. 27 10月, 2009 1 次提交
  6. 16 10月, 2009 1 次提交
    • P
      rcu: Fix TREE_PREEMPT_RCU CPU_HOTPLUG bad-luck hang · 237c80c5
      Paul E. McKenney 提交于
      If the following sequence of events occurs, then
      TREE_PREEMPT_RCU will hang waiting for a grace period to
      complete, eventually OOMing the system:
      
      o	A TREE_PREEMPT_RCU build of the kernel is booted on a system
      	with more than 64 physical CPUs present (32 on a 32-bit system).
      	Alternatively, a TREE_PREEMPT_RCU build of the kernel is booted
      	with RCU_FANOUT set to a sufficiently small value that the
      	physical CPUs populate two or more leaf rcu_node structures.
      
      o	A task is preempted in an RCU read-side critical section
      	while running on a CPU corresponding to a given leaf rcu_node
      	structure.
      
      o	All CPUs corresponding to this same leaf rcu_node structure
      	record quiescent states for the current grace period.
      
      o	All of these same CPUs go offline (hence the need for enough
      	physical CPUs to populate more than one leaf rcu_node structure).
      	This causes the preempted task to be moved to the root rcu_node
      	structure.
      
      At this point, there is nothing left to cause the quiescent
      state to be propagated up the rcu_node tree, so the current
      grace period never completes.
      
      The simplest fix, especially after considering the deadlock
      possibilities, is to detect this situation when the last CPU is
      offlined, and to set that CPU's ->qsmask bit in its leaf
      rcu_node structure.  This will cause the next invocation of
      force_quiescent_state() to end the grace period.
      
      Without this fix, this hang can be triggered in an hour or so on
      some machines with rcutorture and random CPU onlining/offlining.
      With this fix, these same machines pass a full 10 hours of this
      sort of abuse.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <20091015162614.GA19131@linux.vnet.ibm.com>
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      237c80c5
  7. 15 10月, 2009 1 次提交
    • P
      rcu: Prevent RCU IPI storms in presence of high call_rcu() load · 37c72e56
      Paul E. McKenney 提交于
      As the number of callbacks on a given CPU rises, invoke
      force_quiescent_state() only every blimit number of callbacks
      (defaults to 10,000), and even then only if no other CPU has
      invoked force_quiescent_state() in the meantime.
      
      This should fix the performance regression reported by Nick.
      Reported-by: NNick Piggin <npiggin@suse.de>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      Cc: jens.axboe@oracle.com
      LKML-Reference: <12555405592133-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      37c72e56
  8. 07 10月, 2009 3 次提交
    • P
      rcu: Place root rcu_node structure in separate lockdep class · 978c0b88
      Paul E. McKenney 提交于
      Before this patch, all of the rcu_node structures were in the same lockdep
      class, so that lockdep would complain when rcu_preempt_offline_tasks()
      acquired the root rcu_node structure's lock while holding one of the leaf
      rcu_nodes' locks.
      
      This patch changes rcu_init_one() to use a separate
      spin_lock_init() for the root rcu_node structure's lock than is
      used for that of all of the rest of the rcu_node structures, which
      puts the root rcu_node structure's lock in its own lockdep class.
      Suggested-by: NPeter Zijlstra <peterz@infradead.org>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12548908983277-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      978c0b88
    • P
      rcu: Make hot-unplugged CPU relinquish its own RCU callbacks · e74f4c45
      Paul E. McKenney 提交于
      The current interaction between RCU and CPU hotplug requires that
      RCU block in CPU notifiers waiting for callbacks to drain.
      
      This can be greatly simplified by having each CPU relinquish its
      own callbacks, and for both _rcu_barrier() and CPU_DEAD notifiers
      to adopt all callbacks that were previously relinquished.
      
      This change also eliminates the possibility of certain types of
      hangs due to the previous practice of waiting for callbacks to be
      invoked from within CPU notifiers.  If you don't every wait, you
      cannot hang.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <1254890898456-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      e74f4c45
    • P
      rcu: Move rcu_barrier() to rcutree · d0ec774c
      Paul E. McKenney 提交于
      Move the existing rcu_barrier() implementation to rcutree.c,
      consistent with the fact that the rcu_barrier() implementation is
      tied quite tightly to the RCU implementation.
      
      This opens the way to simplify and fix rcutree.c's rcu_barrier()
      implementation in a later patch.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12548908982563-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      d0ec774c
  9. 06 10月, 2009 3 次提交
    • P
      rcu: Clean up code based on review feedback from Josh Triplett, part 4 · a0b6c9a7
      Paul E. McKenney 提交于
      These issues identified during an old-fashioned face-to-face code
      review extending over many hours.  This group improves an existing
      abstraction and introduces two new ones.  It also fixes an RCU
      stall-warning bug found while making the other changes.
      
      o	Make RCU_INIT_FLAVOR() declare its own variables, removing
      	the need to declare them at each call site.
      
      o	Create an rcu_for_each_leaf() macro that scans the leaf
      	nodes of the rcu_node tree.
      
      o	Create an rcu_for_each_node_breadth_first() macro that does
      	a breadth-first traversal of the rcu_node tree, AKA
      	stepping through the array in index-number order.
      
      o	If all CPUs corresponding to a given leaf rcu_node
      	structure go offline, then any tasks queued on that leaf
      	will be moved to the root rcu_node structure.  Therefore,
      	the stall-warning code must dump out tasks queued on the
      	root rcu_node structure as well as those queued on the leaf
      	rcu_node structures.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12541491934126-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      a0b6c9a7
    • P
      rcu: Clean up code based on review feedback from Josh Triplett, part 3 · 3d76c082
      Paul E. McKenney 提交于
      Whitespace fixes, updated comments, and trivial code movement.
      
      o	Fix whitespace error in RCU_HEAD_INIT()
      
      o	Move "So where is rcu_write_lock()" comment so that it does
      	not come between the rcu_read_unlock() header comment and
      	the rcu_read_unlock() definition.
      
      o	Move the module_param statements for blimit, qhimark, and
      	qlowmark to immediately follow the corresponding
      	definitions.
      
      o	In __rcu_offline_cpu(), move the assignment to rdp_me
      	inside the "if" statement, given that rdp_me is not used
      	outside of that "if" statement.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12541491931164-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      3d76c082
    • P
      rcu: Fix rcu_lock_map build failure on CONFIG_PROVE_LOCKING=y · 162cc279
      Paul E. McKenney 提交于
      Move the rcu_lock_map definition from rcutree.c to rcupdate.c so that
      TINY_RCU can use lockdep.
      Reported-by: NIngo Molnar <mingo@elte.hu>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      162cc279
  10. 24 9月, 2009 3 次提交
    • P
      rcu: Clean up code to address Ingo's checkpatch feedback · 9b2619af
      Paul E. McKenney 提交于
      Move declarations and update storage classes to make checkpatch happy.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12537246441701-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      9b2619af
    • P
      rcu: Clean up code based on review feedback from Josh Triplett, part 2 · 1eba8f84
      Paul E. McKenney 提交于
      These issues identified during an old-fashioned face-to-face code
      review extending over many hours.
      
      o	Add comments for tricky parts of code, and correct comments
      	that have passed their sell-by date.
      
      o	Get rid of the vestiges of rcu_init_sched(), which is no
      	longer needed now that PREEMPT_RCU is gone.
      
      o	Move the #include of rcutree_plugin.h to the end of
      	rcutree.c, which means that, rather than having a random
      	collection of forward declarations, the new set of forward
      	declarations document the set of plugins.  The new home for
      	this #include also allows __rcu_init_preempt() to move into
      	rcutree_plugin.h.
      
      o	Fix rcu_preempt_check_callbacks() to be static.
      Suggested-by: NJosh Triplett <josh@joshtriplett.org>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12537246443924-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      Peter Zijlstra <peterz@infradead.org>
      1eba8f84
    • P
      rcu: Clean up code based on review feedback from Josh Triplett · fc2219d4
      Paul E. McKenney 提交于
      These issues identified during an old-fashioned face-to-face code
      review extended over many hours.
      
      o	Bury various forms of the "rsp->completed == rsp->gpnum"
      	comparison into an rcu_gp_in_progress() function, which has
      	the beneficial side-effect of forcing consistent use of
      	ACCESS_ONCE().
      
      o	Replace hand-coded arithmetic with DIV_ROUND_UP().
      
      o	Bury several "!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x01])"
      	instances into an rcu_preempted_readers() function, as this
      	expression indicates that there are no readers blocked
      	within RCU read-side critical sections blocking the current
      	grace period.  (Though there might well be similar readers
      	blocking the next grace period.)
      
      o	Remove a dangling rcu_restart_cpu() declaration that has
      	been dangling for almost 20 minor releases of the kernel.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Acked-by: NPeter Zijlstra <peterz@infradead.org>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <12537246442687-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      fc2219d4
  11. 19 9月, 2009 4 次提交
    • P
      rcu: Fix whitespace inconsistencies · a71fca58
      Paul E. McKenney 提交于
      Fix a number of whitespace ^Ierrors in the include/linux/rcu*
      and the kernel/rcu* files.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      LKML-Reference: <20090918172819.GA24405@linux.vnet.ibm.com>
      [ did more checkpatch fixlets ]
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      a71fca58
    • P
      rcu: Fix thinko, actually initialize full tree · 49e29126
      Paul E. McKenney 提交于
      Commit de078d87 ("rcu: Need to update rnp->gpnum if preemptable RCU
      is to be reliable") repeatedly and incorrectly initializes the root
      rcu_node structure's ->gpnum field rather than initializing the
      ->gpnum field of each node in the tree.  Fix this.  Also add an
      additional consistency check to catch this in the future.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      LKML-Reference: <125329262011-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      49e29126
    • P
      rcu: Apply results of code inspection of kernel/rcutree_plugin.h · e7d8842e
      Paul E. McKenney 提交于
      o Drop the calls to cpu_quiet() from the online/offline code.
        These are unnecessary, since force_quiescent_state() will
        clean up, and removing them simplifies the code a bit.
      
      o Add a warning to check that we don't enqueue the same blocked
        task twice onto the ->blocked_tasks[] lists.
      
      o Rework the phase computation in rcu_preempt_note_context_switch()
        to be more readable, as suggested by Josh Triplett.
      
      o Disable irqs to close a race between the scheduling clock
        interrupt and rcu_preempt_note_context_switch() WRT the
        ->rcu_read_unlock_special field.
      
      o Add comments to rnp->lock acquisition and release within
        rcu_read_unlock_special() noting that irqs are already
        disabled.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      LKML-Reference: <12532926201851-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      e7d8842e
    • P
      rcu: Add WARN_ON_ONCE() consistency checks covering state transitions · 28ecd580
      Paul E. McKenney 提交于
      o Verify that qsmask bits stay clear through GP
        initialization.
      
      o Verify that cpu_quiet_msk_finish() is never invoked unless
        there actually is an RCU grace period in progress.
      
      o Verify that all internal-node rcu_node structures have empty
        blocked_tasks[] lists.
      
      o Verify that child rcu_node structure's bits remain clear after
        acquiring parent's lock.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      LKML-Reference: <12532926191947-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      28ecd580
  12. 18 9月, 2009 4 次提交
    • P
      rcu: Simplify rcu_read_unlock_special() quiescent-state accounting · c3422bea
      Paul E. McKenney 提交于
      The earlier approach required two scheduling-clock ticks to note an
      preemptable-RCU quiescent state in the situation in which the
      scheduling-clock interrupt is unlucky enough to always interrupt an
      RCU read-side critical section.
      
      With this change, the quiescent state is instead noted by the
      outermost rcu_read_unlock() immediately following the first
      scheduling-clock tick, or, alternatively, by the first subsequent
      context switch.  Therefore, this change also speeds up grace
      periods.
      Suggested-by: NJosh Triplett <josh@joshtriplett.org>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      LKML-Reference: <12528585111945-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      c3422bea
    • P
      rcu: Add debug checks to TREE_PREEMPT_RCU for premature grace periods · b0e165c0
      Paul E. McKenney 提交于
      Check to make sure that there are no blocked tasks for the previous
      grace period while initializing for the next grace period, verify
      that rcu_preempt_qs() is given the correct CPU number and is never
      called for an offline CPU.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      LKML-Reference: <12528585111986-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      b0e165c0
    • P
      rcu: Initialize multi-level RCU grace periods holding locks · b835db1f
      Paul E. McKenney 提交于
      Prior implementations initialized the root and any internal
      nodes without holding locks, then initialized the leaves
      holding locks.
      
      This is a false economy, as the leaf nodes will usually greatly
      outnumber the root and internal nodes.  Acquiring locks on all
      nodes is conceptually much simpler as well.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Acked-by: NSteven Rostedt <rostedt@goodmis.org>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josht@linux.vnet.ibm.com
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      LKML-Reference: <12524504773190-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      b835db1f
    • P
      rcu: Need to update rnp->gpnum if preemptable RCU is to be reliable · de078d87
      Paul E. McKenney 提交于
      Without this patch, tasks preempted in RCU read-side critical
      sections can fail to block the grace period, given that
      rnp->gpnum is used to determine which rnp->blocked_tasks[]
      element the preempted task is enqueued on.
      
      Before the patch, rnp->gpnum is always zero, so preempted tasks
      are always enqueued on rnp->blocked_tasks[0], which is correct
      only when the current CPU has not checked into the current
      grace period and the grace-period number is even, or,
      similarly, if the current CPU -has- checked into the current
      grace period and the grace-period number is odd.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Acked-by: NSteven Rostedt <rostedt@goodmis.org>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josht@linux.vnet.ibm.com
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      LKML-Reference: <12524504771622-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      de078d87
  13. 29 8月, 2009 2 次提交
  14. 26 8月, 2009 1 次提交
  15. 25 8月, 2009 1 次提交
    • P
      rcu: Add CPU-offline processing for single-node configurations · 33f76148
      Paul E. McKenney 提交于
      Add preemptable-RCU plugin to handle the CPU-offline
      processing.
      
      An additional plugin is forthcoming to handle multinode RCU
      trees, but this current plugin works for configurations up to
      32 CPUs (64 CPUs for 64-bit kernels).
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josht@linux.vnet.ibm.com
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      LKML-Reference: <12511321213336-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      33f76148
  16. 23 8月, 2009 5 次提交
    • P
      rcu: Merge preemptable-RCU functionality into hierarchical RCU · f41d911f
      Paul E. McKenney 提交于
      Create a kernel/rcutree_plugin.h file that contains definitions
      for preemptable RCU (or, under the #else branch of the #ifdef,
      empty definitions for the classic non-preemptable semantics).
      These definitions fit into plugins defined in kernel/rcutree.c
      for this purpose.
      
      This variant of preemptable RCU uses a new algorithm whose
      read-side expense is roughly that of classic hierarchical RCU
      under CONFIG_PREEMPT. This new algorithm's update-side expense
      is similar to that of classic hierarchical RCU, and, in absence
      of read-side preemption or blocking, is exactly that of classic
      hierarchical RCU.  Perhaps more important, this new algorithm
      has a much simpler implementation, saving well over 1,000 lines
      of code compared to mainline's implementation of preemptable
      RCU, which will hopefully be retired in favor of this new
      algorithm.
      
      The simplifications are obtained by maintaining per-task
      nesting state for running tasks, and using a simple
      lock-protected algorithm to handle accounting when tasks block
      within RCU read-side critical sections, making use of lessons
      learned while creating numerous user-level RCU implementations
      over the past 18 months.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josht@linux.vnet.ibm.com
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      LKML-Reference: <12509746134003-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      f41d911f
    • P
      rcu: Simplify rcu_pending()/rcu_check_callbacks() API · a157229c
      Paul E. McKenney 提交于
      All calls from outside RCU are of the form:
      
      	if (rcu_pending(cpu))
      		rcu_check_callbacks(cpu, user);
      
      This is silly, instead we put a call to rcu_pending() in
      rcu_check_callbacks(), and then make the outside calls be to
      rcu_check_callbacks().  This cuts down on the code a bit and
      also gives the compiler a better chance of optimizing.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josht@linux.vnet.ibm.com
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      LKML-Reference: <125097461311-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      a157229c
    • P
      rcu: Merge per-RCU-flavor initialization into pre-existing macro · 65cf8f86
      Paul E. McKenney 提交于
      Rename the RCU_DATA_PTR_INIT() macro to RCU_INIT_FLAVOR() and
      make it do the rcu_init_one() and rcu_boot_init_percpu_data()
      calls.  Merge the loop that was in the original macro with the
      loops that were in __rcu_init().
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josht@linux.vnet.ibm.com
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      LKML-Reference: <12509746133916-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      65cf8f86
    • P
      rcu: Renamings to increase RCU clarity · d6714c22
      Paul E. McKenney 提交于
      Make RCU-sched, RCU-bh, and RCU-preempt be underlying
      implementations, with "RCU" defined in terms of one of the
      three.  Update the outdated rcu_qsctr_inc() names, as these
      functions no longer increment anything.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josht@linux.vnet.ibm.com
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      LKML-Reference: <12509746132696-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      d6714c22
    • P
      rcu: Move private definitions from include/linux/rcutree.h to kernel/rcutree.h · 9f77da9f
      Paul E. McKenney 提交于
      Some information hiding that makes it easier to merge
      preemptability into rcutree without descending into #include
      hell.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josht@linux.vnet.ibm.com
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      LKML-Reference: <1250974613373-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      9f77da9f
  17. 16 8月, 2009 2 次提交
    • P
      rcu: Simplify RCU CPU-hotplug notification · 2e597558
      Paul E. McKenney 提交于
      Use the new cpu_notifier() API to simplify RCU's CPU-hotplug
      notifiers, collapsing down to a single such notifier.
      
      This makes it trivial to provide the notifier-ordering
      guarantee that rcu_barrier() depends on.
      
      Also remove redundant open_softirq() calls from Hierarchical
      RCU notifier.
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: josht@linux.vnet.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: hugh.dickins@tiscali.co.uk
      Cc: benh@kernel.crashing.org
      LKML-Reference: <12503552312510-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      2e597558
    • P
      rcu: Split hierarchical RCU initialization into boot-time and CPU-online pieces · 27569620
      Paul E. McKenney 提交于
      This patch divides the rcutree initialization into boot-time
      and hotplug-time components, so that the tree data structures
      are guaranteed to be fully linked at boot time regardless of
      what might happen in CPU hotplug operations.
      
      This makes RCU more resilient against CPU hotplug misbehavior
      (and vice versa), but more importantly, does a better job of
      compartmentalizing the code.
      Reported-by: NIngo Molnar <mingo@elte.hu>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: josht@linux.vnet.ibm.com
      Cc: akpm@linux-foundation.org
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: hugh.dickins@tiscali.co.uk
      Cc: benh@kernel.crashing.org
      LKML-Reference: <1250355231152-git-send-email->
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      27569620
  18. 02 8月, 2009 1 次提交
    • I
      debug lockups: Improve lockup detection · c1dc0b9c
      Ingo Molnar 提交于
      When debugging a recent lockup bug i found various deficiencies
      in how our current lockup detection helpers work:
      
       - SysRq-L is not very efficient as it uses a workqueue, hence
         it cannot punch through hard lockups and cannot see through
         most soft lockups either.
      
       - The SysRq-L code depends on the NMI watchdog - which is off
         by default.
      
       - We dont print backtraces from the RCU code's built-in
         'RCU state machine is stuck' debug code. This debug
         code tends to be one of the first (and only) mechanisms
         that show that a lockup has occured.
      
      This patch changes the code so taht we:
      
       - Trigger the NMI backtrace code from SysRq-L instead of using
         a workqueue (which cannot punch through hard lockups)
      
       - Trigger print-all-CPU-backtraces from the RCU lockup detection
         code
      
      Also decouple the backtrace printing code from the NMI watchdog:
      
       - Dont use variable size cpumasks (it might not be initialized
         and they are a bit more fragile anyway)
      
       - Trigger an NMI immediately via an IPI, instead of waiting
         for the NMI tick to occur. This is a lot faster and can
         produce more relevant backtraces. It will also work if the
         NMI watchdog is disabled.
      
       - Dont print the 'dazed and confused' message when we print
         a backtrace from the NMI
      
       - Do a show_regs() plus a dump_stack() to get maximum info
         out of the dump. Worst-case we get two stacktraces - which
         is not a big deal. Sometimes, if register content is
         corrupted, the precise stack walker in show_regs() wont
         give us a full backtrace - in this case dump_stack() will
         do it.
      
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      LKML-Reference: <new-submission>
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      c1dc0b9c