Re: 2.6.0-test6-mm4 - oops in __aio_run_iocbs()

[Daniel McNeil]

On Thu, 2003-10-09 at 04:16, Suparna Bhattacharya wrote:
> On Wed, Oct 08, 2003 at 04:18:15PM -0700, Daniel McNeil wrote:
> > I'm been testing AIO on test6-mm4 using a ext3 file system and
> > copying a 88MB file to an already existing preallocated file of 88MB.
> > I been using my aiocp program to copy the file using i/o sizes of
> > 1k to 512k and outstanding aio requests of between 1 and 64 using
> > O_DIRECT, O_SYNC and O_DIRECT & O_SYNC.  Everything works as long
> > as the file is pre-allocated.  When copying the file to a new file
> > (O_CREAT|O_DIRECT), I get the following oops:
> 
> What are the i/o sizes and block sizes for which you get the oops ?
> Is this only for large i/o sizes ?


I've done more testing and it is a little confusing.
I originally got the oops running a shell script which copied 4
88MB files one at a time to a sub-directory:

for i in fff ff1 ff2 ff3
do
        aiocp -b 128k -n 8 -f CREAT -f DIRECT $i junkdir/$i
done
sync

This script would always cause the oops and the machine would lock up.

I ran aiocp manually using different block sizes (4k-128k) to copy
1 file to a subdirectory.  I removed the file in the subdirectory
afterward.  These tests completed without any problems or oopses.

> __aio_run_iocbs should have been called only for buffered i/o, 
> so this sounds like an O_DIRECT fallback to buffered i/o.
> Possibly after already submitting some blocks direct to BIO,
> the i/o completion path for which ends up calling aio_complete
> releasing the iocb. That could explain the use-after-free situation
> you see.

mm4 has my extra iocb ref count for retries patch.  So the iocb should
not be being freed by aio_complete.  The stack trace looks like the
fault is on the ctx or ctx->runlist.

> 
> But, O_DIRECT write should fallback to buffered i/o only if it 
> encounters holes in the middle of the file, not for simple appends 
> as in your case. Need to figure out how this could have happened ...
> 
> Could you try placing a few printks to find out if this is 
> the case or if we need to look elsewhere ?

I'll do more debugging and let you know what I find.

Daniel

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