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  1. 13 5月, 2015 1 次提交
    • S
      locking/rtmutex: Drop usage of __HAVE_ARCH_CMPXCHG · cede8841
      由 Sebastian Andrzej Siewior 提交于 
      The rtmutex code is the only user of __HAVE_ARCH_CMPXCHG and we have a few
other user of cmpxchg() which do not care about __HAVE_ARCH_CMPXCHG. This
define was first introduced in 23f78d4a ("[PATCH] pi-futex: rt mutex core")
which is v2.6.18. The generic cmpxchg was introduced later in 068fbad2
("Add cmpxchg_local to asm-generic for per cpu atomic operations") which is
v2.6.25.
Back then something was required to get rtmutex working with the fast
path on architectures without cmpxchg and this seems to be the result.

It popped up recently on rt-users because ARM (v6+) does not define
__HAVE_ARCH_CMPXCHG (even that it implements it) which results in slower
locking performance in the fast path.
To put some numbers on it: preempt -RT, am335x, 10 loops of
100000 invocations of rt_spin_lock() + rt_spin_unlock() (time "total" is
the average of the 10 loops for the 100000 invocations, "loop" is
"total / 100000 * 1000"):

     cmpxchg |    slowpath used  ||    cmpxchg used
             |   total   | loop  ||   total    | loop
     --------|-----------|-------||------------|-------
     ARMv6   | 9129.4 us | 91 ns ||  3311.9 us |  33 ns
     generic | 9360.2 us | 94 ns || 10834.6 us | 108 ns
     ----------------------------||--------------------

Forcing it to generic cmpxchg() made things worse for the slowpath and
even worse in cmpxchg() path. It boils down to 14ns more per lock+unlock
in a cache hot loop so it might not be that much in real world.
The last test was a substitute for pre ARMv6 machine but then I was able
to perform the comparison on imx28 which is ARMv5 and therefore is
always is using the generic cmpxchg implementation. And the numbers:

              |   total     | loop
     -------- |-----------  |--------
     slowpath | 263937.2 us | 2639 ns
     cmpxchg  |  16934.2 us |  169 ns
     --------------------------------

The numbers are larger since the machine is slower in general. However,
letting rtmutex use cmpxchg() instead the slowpath seem to improve things.

Since from the ARM (tested on am335x + imx28) point of view always
using cmpxchg() in rt_mutex_lock() + rt_mutex_unlock() makes sense I
would drop the define.
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: will.deacon@arm.com
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20150225175613.GE6823@linutronix.deSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
      cede8841
  3. 12 5月, 2015 1 次提交
  5. 11 5月, 2015 2 次提交
  7. 08 5月, 2015 8 次提交
    • W
      locking/pvqspinlock: Implement simple paravirt support for the qspinlock · a23db284
      由 Waiman Long 提交于 
      Provide a separate (second) version of the spin_lock_slowpath for
paravirt along with a special unlock path.

The second slowpath is generated by adding a few pv hooks to the
normal slowpath, but where those will compile away for the native
case, they expand into special wait/wake code for the pv version.

The actual MCS queue can use extra storage in the mcs_nodes[] array to
keep track of state and therefore uses directed wakeups.

The head contender has no such storage directly visible to the
unlocker.  So the unlocker searches a hash table with open addressing
using a simple binary Galois linear feedback shift register.
Suggested-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1429901803-29771-9-git-send-email-Waiman.Long@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      a23db284
    • P
      locking/qspinlock: Revert to test-and-set on hypervisors · 2aa79af6
      由 Peter Zijlstra (Intel) 提交于 
      When we detect a hypervisor (!paravirt, see qspinlock paravirt support
patches), revert to a simple test-and-set lock to avoid the horrors
of queue preemption.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1429901803-29771-8-git-send-email-Waiman.Long@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      2aa79af6
    • W
      locking/qspinlock: Use a simple write to grab the lock · 2c83e8e9
      由 Waiman Long 提交于 
      Currently, atomic_cmpxchg() is used to get the lock. However, this
is not really necessary if there is more than one task in the queue
and the queue head don't need to reset the tail code. For that case,
a simple write to set the lock bit is enough as the queue head will
be the only one eligible to get the lock as long as it checks that
both the lock and pending bits are not set. The current pending bit
waiting code will ensure that the bit will not be set as soon as the
tail code in the lock is set.

With that change, the are some slight improvement in the performance
of the queued spinlock in the 5M loop micro-benchmark run on a 4-socket
Westere-EX machine as shown in the tables below.

		[Standalone/Embedded - same node]
  # of tasks	Before patch	After patch	%Change
  ----------	-----------	----------	-------
       3	 2324/2321	2248/2265	 -3%/-2%
       4	 2890/2896	2819/2831	 -2%/-2%
       5	 3611/3595	3522/3512	 -2%/-2%
       6	 4281/4276	4173/4160	 -3%/-3%
       7	 5018/5001	4875/4861	 -3%/-3%
       8	 5759/5750	5563/5568	 -3%/-3%

		[Standalone/Embedded - different nodes]
  # of tasks	Before patch	After patch	%Change
  ----------	-----------	----------	-------
       3	12242/12237	12087/12093	 -1%/-1%
       4	10688/10696	10507/10521	 -2%/-2%

It was also found that this change produced a much bigger performance
improvement in the newer IvyBridge-EX chip and was essentially to close
the performance gap between the ticket spinlock and queued spinlock.

The disk workload of the AIM7 benchmark was run on a 4-socket
Westmere-EX machine with both ext4 and xfs RAM disks at 3000 users
on a 3.14 based kernel. The results of the test runs were:

                AIM7 XFS Disk Test
  kernel                 JPM    Real Time   Sys Time    Usr Time
  -----                  ---    ---------   --------    --------
  ticketlock            5678233    3.17       96.61       5.81
  qspinlock             5750799    3.13       94.83       5.97

                AIM7 EXT4 Disk Test
  kernel                 JPM    Real Time   Sys Time    Usr Time
  -----                  ---    ---------   --------    --------
  ticketlock            1114551   16.15      509.72       7.11
  qspinlock             2184466    8.24      232.99       6.01

The ext4 filesystem run had a much higher spinlock contention than
the xfs filesystem run.

The "ebizzy -m" test was also run with the following results:

  kernel               records/s  Real Time   Sys Time    Usr Time
  -----                ---------  ---------   --------    --------
  ticketlock             2075       10.00      216.35       3.49
  qspinlock              3023       10.00      198.20       4.80
Signed-off-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1429901803-29771-7-git-send-email-Waiman.Long@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      2c83e8e9
    • P
      locking/qspinlock: Optimize for smaller NR_CPUS · 69f9cae9
      由 Peter Zijlstra (Intel) 提交于 
      When we allow for a max NR_CPUS < 2^14 we can optimize the pending
wait-acquire and the xchg_tail() operations.

By growing the pending bit to a byte, we reduce the tail to 16bit.
This means we can use xchg16 for the tail part and do away with all
the repeated compxchg() operations.

This in turn allows us to unconditionally acquire; the locked state
as observed by the wait loops cannot change. And because both locked
and pending are now a full byte we can use simple stores for the
state transition, obviating one atomic operation entirely.

This optimization is needed to make the qspinlock achieve performance
parity with ticket spinlock at light load.

All this is horribly broken on Alpha pre EV56 (and any other arch that
cannot do single-copy atomic byte stores).
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1429901803-29771-6-git-send-email-Waiman.Long@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      69f9cae9
    • W
      locking/qspinlock: Extract out code snippets for the next patch · 6403bd7d
      由 Waiman Long 提交于 
      This is a preparatory patch that extracts out the following 2 code
snippets to prepare for the next performance optimization patch.

 1) the logic for the exchange of new and previous tail code words
    into a new xchg_tail() function.
 2) the logic for clearing the pending bit and setting the locked bit
    into a new clear_pending_set_locked() function.

This patch also simplifies the trylock operation before queuing by
calling queued_spin_trylock() directly.
Signed-off-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1429901803-29771-5-git-send-email-Waiman.Long@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      6403bd7d
    • P
      locking/qspinlock: Add pending bit · c1fb159d
      由 Peter Zijlstra (Intel) 提交于 
      Because the qspinlock needs to touch a second cacheline (the per-cpu
mcs_nodes[]); add a pending bit and allow a single in-word spinner
before we punt to the second cacheline.

It is possible so observe the pending bit without the locked bit when
the last owner has just released but the pending owner has not yet
taken ownership.

In this case we would normally queue -- because the pending bit is
already taken. However, in this case the pending bit is guaranteed
to be released 'soon', therefore wait for it and avoid queueing.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1429901803-29771-4-git-send-email-Waiman.Long@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      c1fb159d
    • W
      locking/qspinlock: Introduce a simple generic 4-byte queued spinlock · a33fda35
      由 Waiman Long 提交于 
      This patch introduces a new generic queued spinlock implementation that
can serve as an alternative to the default ticket spinlock. Compared
with the ticket spinlock, this queued spinlock should be almost as fair
as the ticket spinlock. It has about the same speed in single-thread
and it can be much faster in high contention situations especially when
the spinlock is embedded within the data structure to be protected.

Only in light to moderate contention where the average queue depth
is around 1-3 will this queued spinlock be potentially a bit slower
due to the higher slowpath overhead.

This queued spinlock is especially suit to NUMA machines with a large
number of cores as the chance of spinlock contention is much higher
in those machines. The cost of contention is also higher because of
slower inter-node memory traffic.

Due to the fact that spinlocks are acquired with preemption disabled,
the process will not be migrated to another CPU while it is trying
to get a spinlock. Ignoring interrupt handling, a CPU can only be
contending in one spinlock at any one time. Counting soft IRQ, hard
IRQ and NMI, a CPU can only have a maximum of 4 concurrent lock waiting
activities.  By allocating a set of per-cpu queue nodes and used them
to form a waiting queue, we can encode the queue node address into a
much smaller 24-bit size (including CPU number and queue node index)
leaving one byte for the lock.

Please note that the queue node is only needed when waiting for the
lock. Once the lock is acquired, the queue node can be released to
be used later.
Signed-off-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1429901803-29771-2-git-send-email-Waiman.Long@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      a33fda35
    • W
      locking/rwsem: Reduce spinlock contention in wakeup after up_read()/up_write() · 59aabfc7
      由 Waiman Long 提交于 
      In up_write()/up_read(), rwsem_wake() will be called whenever it
detects that some writers/readers are waiting. The rwsem_wake()
function will take the wait_lock and call __rwsem_do_wake() to do the
real wakeup.  For a heavily contended rwsem, doing a spin_lock() on
wait_lock will cause further contention on the heavily contended rwsem
cacheline resulting in delay in the completion of the up_read/up_write
operations.

This patch makes the wait_lock taking and the call to __rwsem_do_wake()
optional if at least one spinning writer is present. The spinning
writer will be able to take the rwsem and call rwsem_wake() later
when it calls up_write(). With the presence of a spinning writer,
rwsem_wake() will now try to acquire the lock using trylock. If that
fails, it will just quit.
Suggested-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NDavidlohr Bueso <dave@stgolabs.net>
Acked-by: NJason Low <jason.low2@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1430428337-16802-2-git-send-email-Waiman.Long@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      59aabfc7
  9. 17 4月, 2015 1 次提交
    • P
      lockdep: Make print_lock() robust against concurrent release · d7bc3197
      由 Peter Zijlstra 提交于 
      During sysrq's show-held-locks command it is possible that
hlock_class() returns NULL for a given lock. The result is then (after
the warning):

	|BUG: unable to handle kernel NULL pointer dereference at 0000001c
	|IP: [<c1088145>] get_usage_chars+0x5/0x100
	|Call Trace:
	| [<c1088263>] print_lock_name+0x23/0x60
	| [<c1576b57>] print_lock+0x5d/0x7e
	| [<c1088314>] lockdep_print_held_locks+0x74/0xe0
	| [<c1088652>] debug_show_all_locks+0x132/0x1b0
	| [<c1315c48>] sysrq_handle_showlocks+0x8/0x10

This *might* happen because the thread on the other CPU drops the lock
after we are looking ->lockdep_depth and ->held_locks points no longer
to a lock that is held.

The fix here is to simply ignore it and continue.
Reported-by: NAndreas Messerschmid <andreas@linutronix.de>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      d7bc3197
  11. 09 4月, 2015 1 次提交
    • J
      locking/mutex: Further simplify mutex_spin_on_owner() · 01ac33c1
      由 Jason Low 提交于 
      Similar to what Linus suggested for rwsem_spin_on_owner(), in
mutex_spin_on_owner() instead of having while (true) and
breaking out of the spin loop on lock->owner != owner, we can
have the loop directly check for while (lock->owner == owner) to
improve the readability of the code.

It also shrinks the code a bit:

   text    data     bss     dec     hex filename
   3721       0       0    3721     e89 mutex.o.before
   3705       0       0    3705     e79 mutex.o.after
Signed-off-by: NJason Low <jason.low2@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1428521960-5268-2-git-send-email-jason.low2@hp.com
[ Added code generation info. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      01ac33c1
  13. 25 3月, 2015 1 次提交
  15. 23 3月, 2015 1 次提交
    • P
      lockdep: Fix the module unload key range freeing logic · 35a9393c
      由 Peter Zijlstra 提交于 
      Module unload calls lockdep_free_key_range(), which removes entries
from the data structures. Most of the lockdep code OTOH assumes the
data structures are append only; in specific see the comments in
add_lock_to_list() and look_up_lock_class().

Clearly this has only worked by accident; make it work proper. The
actual scenario to make it go boom would involve the memory freed by
the module unlock being re-allocated and re-used for a lock inside of
a rcu-sched grace period. This is a very unlikely scenario, still
better plug the hole.

Use RCU list iteration in all places and ammend the comments.

Change lockdep_free_key_range() to issue a sync_sched() between
removal from the lists and returning -- which results in the memory
being freed. Further ensure the callers are placed correctly and
comment the requirements.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Tsyvarev <tsyvarev@ispras.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      35a9393c
  17. 07 3月, 2015 1 次提交
    • J
      locking/rwsem: Fix lock optimistic spinning when owner is not running · 9198f6ed
      由 Jason Low 提交于 
      Ming reported soft lockups occurring when running xfstest due to
the following tip:locking/core commit:

  b3fd4f03 ("locking/rwsem: Avoid deceiving lock spinners")

When doing optimistic spinning in rwsem, threads should stop
spinning when the lock owner is not running. While a thread is
spinning on owner, if the owner reschedules, owner->on_cpu
returns false and we stop spinning.

However, this commit essentially caused the check to get
ignored because when we break out of the spin loop due to
!on_cpu, we continue spinning if sem->owner != NULL.

This patch fixes this by making sure we stop spinning if the
owner is not running. Furthermore, just like with mutexes,
refactor the code such that we don't have separate checks for
owner_running(). This makes it more straightforward in terms of
why we exit the spin on owner loop and we would also avoid
needing to "guess" why we broke out of the loop to make this
more readable.
Reported-and-tested-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJason Low <jason.low2@hp.com>
Acked-by: NDavidlohr Bueso <dave@stgolabs.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1425714331.2475.388.camel@j-VirtualBoxSigned-off-by: NIngo Molnar <mingo@kernel.org>
      9198f6ed
  19. 01 3月, 2015 1 次提交
  21. 24 2月, 2015 1 次提交
  23. 18 2月, 2015 7 次提交
  25. 04 2月, 2015 4 次提交
  27. 29 1月, 2015 1 次提交
  29. 14 1月, 2015 5 次提交
  31. 09 1月, 2015 1 次提交
  33. 04 1月, 2015 1 次提交
  35. 28 10月, 2014 1 次提交
    • P
      locking/mutex: Don't assume TASK_RUNNING · 6f942a1f
      由 Peter Zijlstra 提交于 
      We're going to make might_sleep() test for TASK_RUNNING, because
blocking without TASK_RUNNING will destroy the task state by setting
it to TASK_RUNNING.

There are a few occasions where its 'valid' to call blocking
primitives (and mutex_lock in particular) and not have TASK_RUNNING,
typically such cases are right before we set TASK_RUNNING anyhow.

Robustify the code by not assuming this; this has the beneficial side
effect of allowing optional code emission for fixing the above
might_sleep() false positives.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: tglx@linutronix.de
Cc: ilya.dryomov@inktank.com
Cc: umgwanakikbuti@gmail.com
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140924082241.988560063@infradead.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>
      6f942a1f
  37. 03 10月, 2014 1 次提交
    • P
      locking/lockdep: Revert qrwlock recusive stuff · 8acd91e8
      由 Peter Zijlstra 提交于 
      Commit f0bab73c ("locking/lockdep: Restrict the use of recursive
read_lock() with qrwlock") changed lockdep to try and conform to the
qrwlock semantics which differ from the traditional rwlock semantics.

In particular qrwlock is fair outside of interrupt context, but in
interrupt context readers will ignore all fairness.

The problem modeling this is that read and write side have different
lock state (interrupts) semantics but we only have a single
representation of these. Therefore lockdep will get confused, thinking
the lock can cause interrupt lock inversions.

So revert it for now; the old rwlock semantics were already imperfectly
modeled and the qrwlock extra won't fit either.

If we want to properly fix this, I think we need to resurrect the work
by Gautham did a few years ago that split the read and write state of
locks:

   http://lwn.net/Articles/332801/

FWIW the locking selftest that would've failed (and was reported by
Borislav earlier) is something like:

  RL(X1);	/* IRQ-ON */
  LOCK(A);
  UNLOCK(A);
  RU(X1);

  IRQ_ENTER();
  RL(X1);	/* IN-IRQ */
  RU(X1);
  IRQ_EXIT();

At which point it would report that because A is an IRQ-unsafe lock we
can suffer the following inversion:

	CPU0		CPU1

	lock(A)
			lock(X1)
			lock(A)
	<IRQ>
	 lock(X1)

And this is 'wrong' because X1 can recurse (assuming the above lock are
in fact read-lock) but lockdep doesn't know about this.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: ego@linux.vnet.ibm.com
Cc: bp@alien8.de
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20140930132600.GA7444@worktop.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      8acd91e8