linux-kernel - Re: [PATCH -next] ashmem: Fix ashmem

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Message-ID: <CAG9bXvkjV6-O3JZH6taVX-dZ1tzbSoqaC_sN00LRszsS4QAnrg@mail.gmail.com>
Date:	Thu, 16 May 2013 16:15:49 +0800
From:	Raul Xiong <raulxiong@...il.com>
To:	Neil Zhang <glacier1980@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Robert Love <rlove@...gle.com>,
	Shankar Brahadeeswaran <shankoo77@...il.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Bjorn Bringert <bringert@...gle.com>,
	devel <devel@...verdev.osuosl.org>,
	Hugh Dickins <hughd@...gle.com>,
	Anjana V Kumar <anjanavk12@...il.com>,
	Dad <akpm@...ux-foundation.org>,
	linux-next <linux-next@...r.kernel.org>
Subject: Re: [PATCH -next] ashmem: Fix ashmem_shrink deadlock.

2013/5/14 Raul Xiong <raulxiong@...il.com>
>
> 2013/5/14 Neil Zhang <glacier1980@...il.com>:
> > 2013/5/14 Greg Kroah-Hartman <gregkh@...uxfoundation.org>:
> >> On Wed, May 01, 2013 at 09:56:13AM -0400, Robert Love wrote:
> >>> Don't acquire ashmem_mutex in ashmem_shrink if we've somehow recursed
> >>> into the
> >>> shrinker code from within ashmem. Just bail out, avoiding a deadlock.
> >>> This is
> >>> fine, as ashmem cache pruning is advisory anyhow.
> >>>
> >>> Signed-off-by: Robert Love <rlove@...gle.com>
> >>> ---
> >>>  drivers/staging/android/ashmem.c | 6 +++++-
> >>>  1 file changed, 5 insertions(+), 1 deletion(-)
> >>
> >> Based on Andrew's review comments, I'll drop this from my queue and wait
> >> for a "better" fix for this.
> >>
> >> thanks,
> >>
> >> greg k-h
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> >> the body of a message to majordomo@...r.kernel.org
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >> Please read the FAQ at  http://www.tux.org/lkml/
> >
> > We found the similar issue these days.
> > Add RaulXiong to paste the call stack.
> >
> > Best Regards,
> > Neil Zhang
>
> Hi all,
> I just encountered this deadlock during some stress test and it can be
> described clearly by below function stack. Please check and suggest a
> formal fix for it.
>
> [<c05d3370>] (__schedule) from [<c05d3818>]
> [<c05d3818>] (schedule_preempt_disabled) from [<c05d2578>]
> [<c05d2578>] (__mutex_lock_slowpath) from [<c05d263c>]
> [<c05d263c>] (mutex_lock) from [<c0441dd8>]
> [<c0441dd8>] (ashmem_shrink) from [<c01ae00c>]
> [<c01ae00c>] (shrink_slab) from [<c01b0ec8>]
> [<c01b0ec8>] (try_to_free_pages) from [<c01a65ec>]
> [<c01a65ec>] (__alloc_pages_nodemask) from [<c01d0414>]
> [<c01d0414>] (new_slab) from [<c05cf3a0>]
> [<c05cf3a0>] (__slab_alloc.isra.46.constprop.52) from [<c01d08cc>]
> [<c01d08cc>] (kmem_cache_alloc) from [<c01b1f6c>]
> [<c01b1f6c>] (shmem_alloc_inode) from [<c01e8d18>]
> [<c01e8d18>] (alloc_inode) from [<c01ea3c4>]
> [<c01ea3c4>] (new_inode_pseudo) from [<c01ea404>]
> [<c01ea404>] (new_inode) from [<c01b157c>]
> [<c01b157c>] (shmem_get_inode) from [<c01b3eac>]
> [<c01b3eac>] (shmem_file_setup) from [<c0441d1c>]
> [<c0441d1c>] (ashmem_mmap) from [<c01c1908>]
> [<c01c1908>] (mmap_region) from [<c01c1eac>]
> [<c01c1eac>] (sys_mmap_pgoff) from [<c0112d80>]
>
> Thanks,
> Raul Xiong



Hi Andrew, Greg,

Any feedback?

The issue happens in such sequence:
ashmem_mmap acquired ashmem_mutex --> ashmem_mutex:shmem_file_setup
called kmem_cache_alloc --> shrink due to low memory --> ashmem_shrink
tries to acquire the same ashmem_mutex -- it blocks here.

I think this reports the bug clearly. Please have a look.


Thanks,
Raul Xiong
--
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