Re: [PATCH] cpuset: Fix memory allocator deadlock

[Tejun Heo]

On Tue, Nov 26, 2013 at 03:03:41PM +0100, Peter Zijlstra wrote:
> Juri hit the below lockdep report:
> 
> [    4.303391] ======================================================
> [    4.303392] [ INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected ]
> [    4.303394] 3.12.0-dl-peterz+ #144 Not tainted
> [    4.303395] ------------------------------------------------------
> [    4.303397] kworker/u4:3/689 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
> [    4.303399]  (&p->mems_allowed_seq){+.+...}, at: [<ffffffff8114e63c>] new_slab+0x6c/0x290
> [    4.303417]
> [    4.303417] and this task is already holding:
> [    4.303418]  (&(&q->__queue_lock)->rlock){..-...}, at: [<ffffffff812d2dfb>] blk_execute_rq_nowait+0x5b/0x100
> [    4.303431] which would create a new lock dependency:
> [    4.303432]  (&(&q->__queue_lock)->rlock){..-...} -> (&p->mems_allowed_seq){+.+...}
> [    4.303436]
> 
> [    4.303898] the dependencies between the lock to be acquired and SOFTIRQ-irq-unsafe lock:
> [    4.303918] -> (&p->mems_allowed_seq){+.+...} ops: 2762 {
> [    4.303922]    HARDIRQ-ON-W at:
> [    4.303923]                     [<ffffffff8108ab9a>] __lock_acquire+0x65a/0x1ff0
> [    4.303926]                     [<ffffffff8108cbe3>] lock_acquire+0x93/0x140
> [    4.303929]                     [<ffffffff81063dd6>] kthreadd+0x86/0x180
> [    4.303931]                     [<ffffffff816ded6c>] ret_from_fork+0x7c/0xb0
> [    4.303933]    SOFTIRQ-ON-W at:
> [    4.303933]                     [<ffffffff8108abcc>] __lock_acquire+0x68c/0x1ff0
> [    4.303935]                     [<ffffffff8108cbe3>] lock_acquire+0x93/0x140
> [    4.303940]                     [<ffffffff81063dd6>] kthreadd+0x86/0x180
> [    4.303955]                     [<ffffffff816ded6c>] ret_from_fork+0x7c/0xb0
> [    4.303959]    INITIAL USE at:
> [    4.303960]                    [<ffffffff8108a884>] __lock_acquire+0x344/0x1ff0
> [    4.303963]                    [<ffffffff8108cbe3>] lock_acquire+0x93/0x140
> [    4.303966]                    [<ffffffff81063dd6>] kthreadd+0x86/0x180
> [    4.303969]                    [<ffffffff816ded6c>] ret_from_fork+0x7c/0xb0
> [    4.303972]  }
> 
> Which reports that we take mems_allowed_seq with interrupts enabled. A
> little digging found that this can only be from
> cpuset_change_task_nodemask().
> 
> This is an actual deadlock because an interrupt doing an allocation will
> hit get_mems_allowed()->...->__read_seqcount_begin(), which will spin
> forever waiting for the write side to complete.
> 
> Cc: John Stultz <john.stultz@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Reported-by: Juri Lelli <juri.lelli@xxxxxxxxx>
> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Applied to cgroup/for-3.13-fixes w/ stable cc'd.

Thanks.

-- 
tejun
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