The patch titled
Subject: ipc/sem.c: Add cond_resched in exit_sme
has been added to the -mm tree. Its filename is
ipc-semc-add-cond_resched-in-exit_sme.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-semc-add-cond_resched-in-exit_sme.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-semc-add-cond_resched-in-exit_sme.patch
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------------------------------------------------------
From: Nikolay Borisov <kernel@xxxxxxxx>
Subject: 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
Stack:
ffffffff8129717c ffff88348d695280 ffff883161b1eea4 ffffea000f2359c0
000480094089b340 ffff881c95553e68 ffff881c95553e68 ffff88348d695280
0000000000000000 00007ffe01ca0170 ffff883217c74280 ffff883217c742e8
Call Trace:
[<ffffffff8129717c>] ? exit_sem+0x7c/0x280
[<ffffffff81055548>] do_exit+0x338/0xb40
[<ffffffff81055dd3>] do_group_exit+0x43/0xd0
[<ffffffff81055e74>] SyS_exit_group+0x14/0x20
[<ffffffff81614f5b>] entry_SYSCALL_64_fastpath+0x16/0x6e
Link: http://lkml.kernel.org/r/1475154992-6363-1-git-send-email-kernel@xxxxxxxx
Signed-off-by: Nikolay Borisov <kernel@xxxxxxxx>
Cc: Herton R. Krzesinski <herton@xxxxxxxxxx>
Cc: Fabian Frederick <fabf@xxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 2 ++
1 file changed, 2 insertions(+)
diff -puN ipc/sem.c~ipc-semc-add-cond_resched-in-exit_sme ipc/sem.c
--- a/ipc/sem.c~ipc-semc-add-cond_resched-in-exit_sme
+++ a/ipc/sem.c
@@ -2105,6 +2105,8 @@ void exit_sem(struct task_struct *tsk)
struct list_head tasks;
int semid, i;
+ cond_resched();
+
rcu_read_lock();
un = list_entry_rcu(ulp->list_proc.next,
struct sem_undo, list_proc);
_
Patches currently in -mm which might be from kernel@xxxxxxxx are
ipc-semc-add-cond_resched-in-exit_sme.patch
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