Re: ext4 2.6.35-rc2 regression (ext4: Make sure the MOVE_EXT ioctlcan't overwrite append-only files)

[Markus Trippelsdorf]

On Sun, Jun 06, 2010 at 07:45:48AM -0400, Theodore Tso wrote:
> 
> 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?
> 
I did a git pull this morning and hit the problem after rebooting. I
then looked in the changelog for recent ext4 commits and found the two
entries. I reverted the first one and the problem was still there. 
Then I reverted the second one and the problem went away. After that I
reverted my last revert and the problem reappeared...

(From that I concluded that 1f5a81e41f8b1a782c68d3843e9ec1bfaadf7d72 was
the root of the problem. But maybe it was just a strange coincident)

I haven't tried a full bisection yet. The last working kernel was just
the git kernel from about 5 days ago. The bug is quiet easy to reproduce
and usually happens right after I boot my system and sometimes when I
shut it down.

I will try a bisection later today.

-- 
Markus
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