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

From: Kamezawa Hiroyuki
Date: Wed Oct 17 2012 - 01:43:20 EST

(2012/10/17 14:24), David Rientjes wrote:
On Wed, 17 Oct 2012, Dave Jones wrote:

BUG: sleeping function called from invalid context at kernel/mutex.c:269
in_atomic(): 1, irqs_disabled(): 0, pid: 8558, name: trinity-child2
3 locks on stack by trinity-child2/8558:
#0: held: (&p->lock){+.+.+.}, instance: ffff88010c9a00b0, at: [<ffffffff8120cd1f>] seq_lseek+0x3f/0x120
#1: held: (&mm->mmap_sem){++++++}, instance: ffff88013956f7c8, at: [<ffffffff81254437>] m_start+0xa7/0x190
#2: held: (&(&p->alloc_lock)->rlock){+.+...}, instance: ffff88011fc64f30, at: [<ffffffff81254f8f>] show_numa_map+0x14f/0x610
Pid: 8558, comm: trinity-child2 Not tainted 3.7.0-rc1+ #32
Call Trace:
[<ffffffff810ae4ec>] __might_sleep+0x14c/0x200
[<ffffffff816bdf4e>] mutex_lock_nested+0x2e/0x50
[<ffffffff811c43a3>] mpol_shared_policy_lookup+0x33/0x90
[<ffffffff8118d5c3>] shmem_get_policy+0x33/0x40
[<ffffffff811c31fa>] get_vma_policy+0x3a/0x90
[<ffffffff81254fa3>] show_numa_map+0x163/0x610
[<ffffffff81255b10>] ? pid_maps_open+0x20/0x20
[<ffffffff81255980>] ? pagemap_hugetlb_range+0xf0/0xf0
[<ffffffff81255483>] show_pid_numa_map+0x13/0x20
[<ffffffff8120c902>] traverse+0xf2/0x230
[<ffffffff8120cd8b>] seq_lseek+0xab/0x120
[<ffffffff811e6c0b>] sys_lseek+0x7b/0xb0
[<ffffffff816ca088>] tracesys+0xe1/0xe6

Hmm, looks like we need to change the refcount semantics entirely. We'll
need to make get_vma_policy() always take a reference and then drop it
accordingly. This work sif get_vma_policy() can grab a reference while
holding task_lock() for the task policy fallback case.

Comments on this approach?

I think this refcounting is better than using task_lock().


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