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  1. 03 12月, 2015 2 次提交
    • O
      cgroup: kill cgrp_ss_priv[CGROUP_CANFORK_COUNT] and friends · b53202e6
      由 Oleg Nesterov 提交于 
      Now that nobody use the "priv" arg passed to can_fork/cancel_fork/fork we can
kill CGROUP_CANFORK_COUNT/SUBSYS_TAG/etc and cgrp_ss_priv[] in copy_process().
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
      b53202e6
    • T
      cgroup: fix handling of multi-destination migration from subtree_control enabling · 1f7dd3e5
      由 Tejun Heo 提交于 
      Consider the following v2 hierarchy.

  P0 (+memory) --- P1 (-memory) --- A
                                 \- B
       
P0 has memory enabled in its subtree_control while P1 doesn't.  If
both A and B contain processes, they would belong to the memory css of
P1.  Now if memory is enabled on P1's subtree_control, memory csses
should be created on both A and B and A's processes should be moved to
the former and B's processes the latter.  IOW, enabling controllers
can cause atomic migrations into different csses.

The core cgroup migration logic has been updated accordingly but the
controller migration methods haven't and still assume that all tasks
migrate to a single target css; furthermore, the methods were fed the
css in which subtree_control was updated which is the parent of the
target csses.  pids controller depends on the migration methods to
move charges and this made the controller attribute charges to the
wrong csses often triggering the following warning by driving a
counter negative.

 WARNING: CPU: 1 PID: 1 at kernel/cgroup_pids.c:97 pids_cancel.constprop.6+0x31/0x40()
 Modules linked in:
 CPU: 1 PID: 1 Comm: systemd Not tainted 4.4.0-rc1+ #29
 ...
  ffffffff81f65382 ffff88007c043b90 ffffffff81551ffc 0000000000000000
  ffff88007c043bc8 ffffffff810de202 ffff88007a752000 ffff88007a29ab00
  ffff88007c043c80 ffff88007a1d8400 0000000000000001 ffff88007c043bd8
 Call Trace:
  [<ffffffff81551ffc>] dump_stack+0x4e/0x82
  [<ffffffff810de202>] warn_slowpath_common+0x82/0xc0
  [<ffffffff810de2fa>] warn_slowpath_null+0x1a/0x20
  [<ffffffff8118e031>] pids_cancel.constprop.6+0x31/0x40
  [<ffffffff8118e0fd>] pids_can_attach+0x6d/0xf0
  [<ffffffff81188a4c>] cgroup_taskset_migrate+0x6c/0x330
  [<ffffffff81188e05>] cgroup_migrate+0xf5/0x190
  [<ffffffff81189016>] cgroup_attach_task+0x176/0x200
  [<ffffffff8118949d>] __cgroup_procs_write+0x2ad/0x460
  [<ffffffff81189684>] cgroup_procs_write+0x14/0x20
  [<ffffffff811854e5>] cgroup_file_write+0x35/0x1c0
  [<ffffffff812e26f1>] kernfs_fop_write+0x141/0x190
  [<ffffffff81265f88>] __vfs_write+0x28/0xe0
  [<ffffffff812666fc>] vfs_write+0xac/0x1a0
  [<ffffffff81267019>] SyS_write+0x49/0xb0
  [<ffffffff81bcef32>] entry_SYSCALL_64_fastpath+0x12/0x76

This patch fixes the bug by removing @css parameter from the three
migration methods, ->can_attach, ->cancel_attach() and ->attach() and
updating cgroup_taskset iteration helpers also return the destination
css in addition to the task being migrated.  All controllers are
updated accordingly.

* Controllers which don't care whether there are one or multiple
  target csses can be converted trivially.  cpu, io, freezer, perf,
  netclassid and netprio fall in this category.

* cpuset's current implementation assumes that there's single source
  and destination and thus doesn't support v2 hierarchy already.  The
  only change made by this patchset is how that single destination css
  is obtained.

* memory migration path already doesn't do anything on v2.  How the
  single destination css is obtained is updated and the prep stage of
  mem_cgroup_can_attach() is reordered to accomodate the change.

* pids is the only controller which was affected by this bug.  It now
  correctly handles multi-destination migrations and no longer causes
  counter underflow from incorrect accounting.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-and-tested-by: NDaniel Wagner <daniel.wagner@bmw-carit.de>
Cc: Aleksa Sarai <cyphar@cyphar.com>
      1f7dd3e5
  3. 23 10月, 2015 1 次提交
  5. 20 10月, 2015 4 次提交
  7. 16 10月, 2015 1 次提交
    • T
      cgroup: keep zombies associated with their original cgroups · 2e91fa7f
      由 Tejun Heo 提交于 
      cgroup_exit() is called when a task exits and disassociates the
exiting task from its cgroups and half-attach it to the root cgroup.
This is unnecessary and undesirable.

No controller actually needs an exiting task to be disassociated with
non-root cgroups.  Both cpu and perf_event controllers update the
association to the root cgroup from their exit callbacks just to keep
consistent with the cgroup core behavior.

Also, this disassociation makes it difficult to track resources held
by zombies or determine where the zombies came from.  Currently, pids
controller is completely broken as it uncharges on exit and zombies
always escape the resource restriction.  With cgroup association being
reset on exit, fixing it is pretty painful.

There's no reason to reset cgroup membership on exit.  The zombie can
be removed from its css_set so that it doesn't show up on
"cgroup.procs" and thus can't be migrated or interfere with cgroup
removal.  It can still pin and point to the css_set so that its cgroup
membership is maintained.  This patch makes cgroup core keep zombies
associated with their cgroups at the time of exit.

* Previous patches decoupled populated_cnt tracking from css_set
  lifetime, so a dying task can be simply unlinked from its css_set
  while pinning and pointing to the css_set.  This keeps css_set
  association from task side alive while hiding it from "cgroup.procs"
  and populated_cnt tracking.  The css_set reference is dropped when
  the task_struct is freed.

* ->exit() callback no longer needs the css arguments as the
  associated css never changes once PF_EXITING is set.  Removed.

* cpu and perf_events controllers no longer need ->exit() callbacks.
  There's no reason to explicitly switch away on exit.  The final
  schedule out is enough.  The callbacks are removed.

* On traditional hierarchies, nothing changes.  "/proc/PID/cgroup"
  still reports "/" for all zombies.  On the default hierarchy,
  "/proc/PID/cgroup" keeps reporting the cgroup that the task belonged
  to at the time of exit.  If the cgroup gets removed before the task
  is reaped, " (deleted)" is appended.

v2: Build brekage due to missing dummy cgroup_free() when
    !CONFIG_CGROUP fixed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
      2e91fa7f
  9. 07 10月, 2015 1 次提交
  11. 06 10月, 2015 13 次提交
  13. 23 9月, 2015 1 次提交
  15. 18 9月, 2015 3 次提交
  17. 13 9月, 2015 7 次提交
  19. 11 9月, 2015 1 次提交
    • W
      sched: 'Annotate' migrate_tasks() · 5473e0cc
      由 Wanpeng Li 提交于 
      Kernel testing triggered this warning:

| WARNING: CPU: 0 PID: 13 at kernel/sched/core.c:1156 do_set_cpus_allowed+0x7e/0x80()
| Modules linked in:
| CPU: 0 PID: 13 Comm: migration/0 Not tainted 4.2.0-rc1-00049-g25834c73 #2
| Call Trace:
|   dump_stack+0x4b/0x75
|   warn_slowpath_common+0x8b/0xc0
|   warn_slowpath_null+0x22/0x30
|   do_set_cpus_allowed+0x7e/0x80
|   cpuset_cpus_allowed_fallback+0x7c/0x170
|   select_fallback_rq+0x221/0x280
|   migration_call+0xe3/0x250
|   notifier_call_chain+0x53/0x70
|   __raw_notifier_call_chain+0x1e/0x30
|   cpu_notify+0x28/0x50
|   take_cpu_down+0x22/0x40
|   multi_cpu_stop+0xd5/0x140
|   cpu_stopper_thread+0xbc/0x170
|   smpboot_thread_fn+0x174/0x2f0
|   kthread+0xc4/0xe0
|   ret_from_kernel_thread+0x21/0x30

As Peterz pointed out:

| So the normal rules for changing task_struct::cpus_allowed are holding
| both pi_lock and rq->lock, such that holding either stabilizes the mask.
|
| This is so that wakeup can happen without rq->lock and load-balance
| without pi_lock.
|
| From this we already get the relaxation that we can omit acquiring
| rq->lock if the task is not on the rq, because in that case
| load-balancing will not apply to it.
|
| ** these are the rules currently tested in do_set_cpus_allowed() **
|
| Now, since __set_cpus_allowed_ptr() uses task_rq_lock() which
| unconditionally acquires both locks, we could get away with holding just
| rq->lock when on_rq for modification because that'd still exclude
| __set_cpus_allowed_ptr(), it would also work against
| __kthread_bind_mask() because that assumes !on_rq.
|
| That said, this is all somewhat fragile.
|
| Now, I don't think dropping rq->lock is quite as disastrous as it
| usually is because !cpu_active at this point, which means load-balance
| will not interfere, but that too is somewhat fragile.
|
| So we end up with a choice of two fragile..

This patch fixes it by following the rules for changing
task_struct::cpus_allowed with both pi_lock and rq->lock held.
Reported-by: Nkernel test robot <ying.huang@intel.com>
Reported-by: NSasha Levin <sasha.levin@oracle.com>
Signed-off-by: NWanpeng Li <wanpeng.li@hotmail.com>
[ Modified changelog and patch. ]
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/BLU436-SMTP1660820490DE202E3934ED3806E0@phx.gblSigned-off-by: NIngo Molnar <mingo@kernel.org>
      5473e0cc
  21. 02 9月, 2015 1 次提交
  23. 25 8月, 2015 1 次提交
    • J
      sched: Fix cpu_active_mask/cpu_online_mask race · dd9d3843
      由 Jan H. Schönherr 提交于 
      There is a race condition in SMP bootup code, which may result
in

    WARNING: CPU: 0 PID: 1 at kernel/workqueue.c:4418
    workqueue_cpu_up_callback()
or
    kernel BUG at kernel/smpboot.c:135!

It can be triggered with a bit of luck in Linux guests running
on busy hosts.

	CPU0                        CPUn
	====                        ====

	_cpu_up()
	  __cpu_up()
				    start_secondary()
				      set_cpu_online()
					cpumask_set_cpu(cpu,
						   to_cpumask(cpu_online_bits));
	  cpu_notify(CPU_ONLINE)
	    <do stuff, see below>
					cpumask_set_cpu(cpu,
						   to_cpumask(cpu_active_bits));

During the various CPU_ONLINE callbacks CPUn is online but not
active. Several things can go wrong at that point, depending on
the scheduling of tasks on CPU0.

Variant 1:

  cpu_notify(CPU_ONLINE)
    workqueue_cpu_up_callback()
      rebind_workers()
        set_cpus_allowed_ptr()

  This call fails because it requires an active CPU; rebind_workers()
  ends with a warning:

    WARNING: CPU: 0 PID: 1 at kernel/workqueue.c:4418
    workqueue_cpu_up_callback()

Variant 2:

  cpu_notify(CPU_ONLINE)
    smpboot_thread_call()
      smpboot_unpark_threads()
       ..
        __kthread_unpark()
          __kthread_bind()
          wake_up_state()
           ..
            select_task_rq()
              select_fallback_rq()

  The ->wake_cpu of the unparked thread is not allowed, making a call
  to select_fallback_rq() necessary. Then, select_fallback_rq() cannot
  find an allowed, active CPU and promptly resets the allowed CPUs, so
  that the task in question ends up on CPU0.

  When those unparked tasks are eventually executed, they run
  immediately into a BUG:

    kernel BUG at kernel/smpboot.c:135!

Just changing the order in which the online/active bits are set
(and adding some memory barriers), would solve the two issues
above. However, it would change the order of operations back to
the one before commit 6acbfb96 ("sched: Fix hotplug vs.
set_cpus_allowed_ptr()"), thus, reintroducing that particular
problem.

Going further back into history, we have at least the following
commits touching this topic:
- commit 2baab4e9 ("sched: Fix select_fallback_rq() vs cpu_active/cpu_online")
- commit 5fbd036b ("sched: Cleanup cpu_active madness")

Together, these give us the following non-working solutions:

  - secondary CPU sets active before online, because active is assumed to
    be a subset of online;

  - secondary CPU sets online before active, because the primary CPU
    assumes that an online CPU is also active;

  - secondary CPU sets online and waits for primary CPU to set active,
    because it might deadlock.

Commit 875ebe94 ("powerpc/smp: Wait until secondaries are
active & online") introduces an arch-specific solution to this
arch-independent problem.

Now, go for a more general solution without explicit waiting and
simply set active twice: once on the secondary CPU after online
was set and once on the primary CPU after online was seen.

set_cpus_allowed_ptr()")
Signed-off-by: NJan H. Schönherr <jschoenh@amazon.de>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@vger.kernel.org>
Cc: Anton Blanchard <anton@samba.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Wilson <msw@amazon.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 6acbfb96 ("sched: Fix hotplug vs. set_cpus_allowed_ptr()")
Link: http://lkml.kernel.org/r/1439408156-18840-1-git-send-email-jschoenh@amazon.deSigned-off-by: NIngo Molnar <mingo@kernel.org>
      dd9d3843
  25. 12 8月, 2015 4 次提交