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Nikolay Borisov 2a1613a586 ipc/sem.c: add cond_resched in exit_sme 
In CONFIG_PREEMPT=n kernel a softlockup was observed while the for loop in
exit_sem.  Apparently it's possible for the loop to take quite a long time
and it doesn't have a scheduling point in it.  Since the codes is
executing under an rcu read section this may also cause rcu stalls, which
in turn block synchronize_rcu operations, which more or less de-stabilises
the whole system.

Fix this by introducing a cond_resched() at the beginning of the loop.

So this patch fixes the following:

  NMI watchdog: BUG: soft lockup - CPU#10 stuck for 23s! [httpd:18119]
  CPU: 10 PID: 18119 Comm: httpd Tainted: G           O    4.4.20-clouder2 #6
  Hardware name: Supermicro X10DRi/X10DRi, BIOS 1.1 04/14/2015
  task: ffff88348d695280 ti: ffff881c95550000 task.ti: ffff881c95550000
  RIP: 0010:[<ffffffff81614bc7>]  [<ffffffff81614bc7>] _raw_spin_lock+0x17/0x30
  RSP: 0018:ffff881c95553e40  EFLAGS: 00000246
  RAX: 0000000000000000 RBX: ffff883161b1eea8 RCX: 000000000000000d
  RDX: 0000000000000001 RSI: 000000000000000e RDI: ffff883161b1eea4
  RBP: ffff881c95553ea0 R08: ffff881c95553e68 R09: ffff883fef376f88
  R10: ffff881fffb58c20 R11: ffffea0072556600 R12: ffff883161b1eea0
  R13: ffff88348d695280 R14: ffff883dec427000 R15: ffff8831621672a0
  FS:  0000000000000000(0000) GS:ffff881fffb40000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f3b3723e020 CR3: 0000000001c0a000 CR4: 00000000001406e0
  Call Trace:
    ? exit_sem+0x7c/0x280
    do_exit+0x338/0xb40
    do_group_exit+0x43/0xd0
    SyS_exit_group+0x14/0x20
    entry_SYSCALL_64_fastpath+0x16/0x6e

Link: http://lkml.kernel.org/r/1475154992-6363-1-git-send-email-kernel@kyup.com
Signed-off-by: Nikolay Borisov <kernel@kyup.com>
Cc: Herton R. Krzesinski <herton@redhat.com>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2016-10-11 15:06:33 -07:00
..
Makefile ipc/msg: increase MSGMNI, remove scaling 2014-12-13 12:42:52 -08:00
compat.c ipc: resolve shadow warnings 2014-10-14 02:18:23 +02:00
compat_mq.c ipc, kernel: use Linux headers 2014-06-06 16:08:14 -07:00
ipc_sysctl.c ipc/msg: increase MSGMNI, remove scaling 2014-12-13 12:42:52 -08:00
mq_sysctl.c ipc: convert use of typedef ctl_table to struct ctl_table 2014-06-06 16:08:16 -07:00
mqueue.c fs: Replace CURRENT_TIME with current_time() for inode timestamps 2016-09-27 21:06:21 -04:00
msg.c ipc/msg: avoid waking sender upon full queue 2016-10-11 15:06:33 -07:00
msgutil.c ipc: delete "nr_ipc_ns" 2016-08-02 19:35:44 -04:00
namespace.c Merge branch 'nsfs-ioctls' into HEAD 2016-09-22 20:00:36 -05:00
sem.c ipc/sem.c: add cond_resched in exit_sme 2016-10-11 15:06:33 -07:00
shm.c shmem: make shmem_inode_info::lock irq-safe 2016-07-26 16:19:19 -07:00
syscall.c
…
util.c tree wide: use kvfree() than conditional kfree()/vfree() 2016-01-22 17:02:18 -08:00
util.h tree wide: use kvfree() than conditional kfree()/vfree() 2016-01-22 17:02:18 -08:00