linux-kernel - Re: shmem_getpage_gfp VM_BUG

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Message-ID: <20121101232030.GA25519@redhat.com>
Date:	Thu, 1 Nov 2012 19:20:30 -0400
From:	Dave Jones <davej@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: shmem_getpage_gfp VM_BUG_ON triggered. [3.7rc2]

On Thu, Nov 01, 2012 at 04:03:40PM -0700, Hugh Dickins wrote:
 > > I just noticed we had a user report hitting this same warning, but
 > > with a different trace..
 > > 
 > > : [<ffffffff8105b84f>] warn_slowpath_common+0x7f/0xc0
 > > : [<ffffffff8105b8aa>] warn_slowpath_null+0x1a/0x20
 > > : [<ffffffff81143c73>] shmem_getpage_gfp+0x7f3/0x830
 > > : [<ffffffff81158c9d>] ? vma_adjust+0x3ed/0x620
 > > : [<ffffffff81143f02>] shmem_file_aio_read+0x1f2/0x380
 > > : [<ffffffff8118e487>] do_sync_read+0xa7/0xe0
 > > : [<ffffffff8118eda9>] vfs_read+0xa9/0x180
 > > : [<ffffffff8118eeca>] sys_read+0x4a/0x90
 > > : [<ffffffff816226e9>] system_call_fastpath+0x16/0x1b
 > 
 > Equally explicable by Hannes's hypothesis;
 > but useful supporting evidence, thank you.
 > 
 > Except... earlier in the thread you explained how you hacked
 > #define VM_BUG_ON(cond) WARN_ON(cond)
 > to get this to come out as a warning instead of a bug,
 > and now it looks as if "a user" has here done the same.
 > 
 > Which is very much a user's right, of course; but does
 > make me wonder whether that user might actually be davej ;)

indirectly. I made the same change in the Fedora kernel a while ago
to test a hypothesis that we weren't getting any VM_BUG_ON reports.

	Dave

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