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

[David Rientjes]

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.
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