linux-kernel - Re: ext4 2.6.35-rc2 regression (ext4: Make sure the MOVE_EXT ioctl can't overwrite append-only files)

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Date:	Sun, 6 Jun 2010 07:45:48 -0400
From:	Theodore Tso <tytso@....EDU>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	linux-ext4@...r.kernel.org
Subject: Re: ext4 2.6.35-rc2 regression (ext4: Make sure the MOVE_EXT ioctl can't overwrite append-only files)


On Jun 6, 2010, at 4:16 AM, Markus Trippelsdorf wrote:

> Commit 1f5a81e41f8b1a782c68d3843e9ec1bfaadf7d72
> "ext4: Make sure the MOVE_EXT ioctl can't overwrite append-only files"
> causes the following kernel BUG on my machine (x86_64):
> 
> BUG: Bad page map in process mpd  pte:720072000000000 pmd:11d2f7067
> addr:00007f6b09f82000 vm_flags:08000070 anon_vma:(null) mapping:ffff88011b1cec18 index:132
> vma->vm_ops->fault: filemap_fault+0x0/0x31e
> vma->vm_file->f_op->mmap: ext4_file_mmap+0x0/0x54
> Pid: 1672, comm: mpd Not tainted 2.6.35-rc2-00032-g78a5aa2 #45
> Call Trace:
> [<ffffffff810b7a35>] print_bad_pte+0x1d0/0x1e9
> [<ffffffff810b8c9b>] unmap_vmas+0x50c/0x803
> [<ffffffff810be003>] exit_mmap+0xc4/0x14a
> [<ffffffff81057bc6>] mmput+0x2d/0xb9

What makes you think it was the commit you cited that is causing this crash?  Unless you are specifically using e2defrag (or write code which explicitly calls this ext4-specific ioctl), the code path in question wouldn't even be entered, and I see nothing in this stack trace to indicate it was caused by this change.

(And in fact in a subsequent e-mail I see that you've tried reverting both changes to ext4 between rc1 and rc2 and it didn't seem to help.)

Have you tried bisecting the kernel to find commit which introduced this problem?   What was the last kernel that didn't have these problem for you?  -rc1?   How easy is this to reproduce?   Does this happen as soon as you boot up your system?

Thanks,

-- Ted

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