Re: [patch for-3.7] mm, mempolicy: fix printing stack contents in numa_maps

[KOSAKI Motohiro <kosaki.motohiro@gmail.com>]

On Wed, Oct 24, 2012 at 8:08 PM, David Rientjes <rientjes@google.com> wrote:
> On Wed, 24 Oct 2012, Sasha Levin wrote:
>
>> > This should be fixed by 9e7814404b77 ("hold task->mempolicy while
>> > numa_maps scans.") in 3.7-rc2, can you reproduce any issues reading
>> > /proc/pid/numa_maps on that kernel?
>>
>> I was actually referring to the warnings Dave Jones saw when fuzzing
>> with trinity after the
>> original patch was applied.
>>
>> I still see the following when fuzzing:
>>
>> [  338.467156] BUG: sleeping function called from invalid context at
>> kernel/mutex.c:269
>> [  338.473719] in_atomic(): 1, irqs_disabled(): 0, pid: 6361, name: trinity-main
>> [  338.481199] 2 locks held by trinity-main/6361:
>> [  338.486629]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810aa314>]
>> __do_page_fault+0x1e4/0x4f0
>> [  338.498783]  #1:  (&(&mm->page_table_lock)->rlock){+.+...}, at:
>> [<ffffffff8122f017>] handle_pte_fault+0x3f7/0x6a0
>> [  338.511409] Pid: 6361, comm: trinity-main Tainted: G        W
>> 3.7.0-rc2-next-20121024-sasha-00001-gd95ef01-dirty #74
>> [  338.530318] Call Trace:
>> [  338.534088]  [<ffffffff8114e393>] __might_sleep+0x1c3/0x1e0
>> [  338.539358]  [<ffffffff83ae5209>] mutex_lock_nested+0x29/0x50
>> [  338.545253]  [<ffffffff8124fc3e>] mpol_shared_policy_lookup+0x2e/0x90
>> [  338.545258]  [<ffffffff81219ebe>] shmem_get_policy+0x2e/0x30
>> [  338.545264]  [<ffffffff8124e99a>] get_vma_policy+0x5a/0xa0
>> [  338.545267]  [<ffffffff8124fce1>] mpol_misplaced+0x41/0x1d0
>> [  338.545272]  [<ffffffff8122f085>] handle_pte_fault+0x465/0x6a0
>> [  338.545278]  [<ffffffff81131e04>] ? __rcu_read_unlock+0x44/0xb0
>> [  338.545282]  [<ffffffff81230baa>] handle_mm_fault+0x32a/0x360
>> [  338.545286]  [<ffffffff810aa5b0>] __do_page_fault+0x480/0x4f0
>> [  338.545293]  [<ffffffff8111a706>] ? del_timer+0x26/0x80
>> [  338.545298]  [<ffffffff811c7313>] ? rcu_cleanup_after_idle+0x23/0x170
>> [  338.545302]  [<ffffffff811ca9a4>] ? rcu_eqs_exit_common+0x64/0x3a0
>> [  338.545305]  [<ffffffff811c8c66>] ? rcu_eqs_enter_common+0x7c6/0x970
>> [  338.545309]  [<ffffffff811cafdc>] ? rcu_eqs_exit+0x9c/0xb0
>> [  338.545312]  [<ffffffff810aa666>] do_page_fault+0x26/0x40
>> [  338.545317]  [<ffffffff810a3a40>] do_async_page_fault+0x30/0xa0
>> [  338.545321]  [<ffffffff83ae9268>] async_page_fault+0x28/0x30
>>
>
> Ok, this looks the same but it's actually a different issue:
> mpol_misplaced(), which now only exists in linux-next and not in 3.7-rc2,
> calls get_vma_policy() which may take the shared policy mutex.  This
> happens while holding page_table_lock from do_huge_pmd_numa_page() but
> also from do_numa_page() while holding a spinlock on the ptl, which is
> coming from the sched/numa branch.
>
> Is there anyway that we can avoid changing the shared policy mutex back
> into a spinlock (it was converted in b22d127a39dd ["mempolicy: fix a race
> in shared_policy_replace()"])?
>
> Adding Peter, Rik, and Mel to the cc.

Hrm. I haven't noticed there is mpol_misplaced() in linux-next. Peter,
I guess you commited it, right? If so, may I review your mempolicy
changes? Now mempolicy has a lot of horrible buggy code and I hope to
maintain carefully. Which tree should i see?

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