http://oss.sgi.com/pipermail/xfs/2010-December/048691.html
I have always seen the hang problem comes only if comes when b_relse != NULL, and b_hold > 2I have made below workaround it solved the problem in our case because when USB is removed we know we get EIO error.
But I think we need to review xfs_buf_error_relse() and xfs_buf_relse() considering XBF_LOCK flow path.
@@ -1047,9 +1047,19 @@ xfs_buf_iodone_callbacks(
/* We actually overwrite the existing b-relse
function at times, but we're gonna be shutting down
anyway. */
- XFS_BUF_SET_BRELSE_FUNC(bp,xfs_buf_error_relse);
- XFS_BUF_DONE(bp);
- XFS_BUF_FINISH_IOWAIT(bp);
+ if (XFS_BUF_GETERROR(bp) == EIO){
+ ASSERT(XFS_BUF_TARGET(bp) == mp->m_ddev_targp);
+ XFS_BUF_SUPER_STALE(bp);
+ trace_xfs_buf_item_iodone(bp, _RET_IP_);
+ xfs_buf_do_callbacks(bp, lip);
+ XFS_BUF_SET_FSPRIVATE(bp, NULL);
+ XFS_BUF_CLR_IODONE_FUNC(bp);
+ xfs_biodone(bp);
+ } else {
+ XFS_BUF_SET_BRELSE_FUNC(bp,xfs_buf_error_relse);
+ XFS_BUF_DONE(bp);
+ XFS_BUF_FINISH_IOWAIT(bp);
+ }
}
return;
}
Dec 31, 2010 at 4:43 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
On Thu, Dec 30, 2010 at 05:58:36PM +0530, Ajeet Yadav wrote:FWIW, in future can you please report what kernel you are testing on?
> Kernel: 2.6.30.9
>
> I am trouble shooting a hang in XFS during umount.
> Test scenerio: Copy large number of files files using below script, and
> remove the USB after 3-5 second
This appears to be the same problem as reported here:
>
> index=0
> while [ "$?" == 0 ]
> do
> index=$((index+1))
> sync
> cp $1/1KB.txt $2/"$index".test
> done
>
> In rare scenerio during USB unplug the umount process hang at xfs_buf_lock.
> Below log shows the hung process
>
> We have put printk to buffer handling functions xfs_buf_iodone_callbacks(),
> xfs_buf_error_relse(), xfs_buf_relse() and xfs_buf_rele()
>
> We always observed the hang only comes when bp->b_relse =
> xfs_buf_error_relse(). i.e when xfs_buf_iodone_callbacks() execute
> XFS_BUF_SET_BRELSE_FUNC(bp,xfs_buf_error_relse);
> XFS_BUF_DONE(bp);
> XFS_BUF_FINISH_IOWAIT(bp);
>
> buf its never called by xfs_buf_relse() because b_hold = 3.
>
> Also we have seen that this problem always comes when bp->relse != NULL &&
> bp->hold > 1.
http://oss.sgi.com/archives/xfs/2010-12/msg00380.html
If you have a recent enough kernel, you can get all this information
> I do not know whether below prints will help you, but I have taken printk
> for super block buffer tracing
> S-functionname ( Start of function)
> E-functionname (End of function)
from the tracing built into XFS.
As it is, the cause of the problem is that setting bp->b_relse
changes the behaviour of xfs_buf_relse() - if bp->b_relse is set, it
doesn't unlock the buffer. This is normally just fine, because
xfs_buf_rele() has a special case to handle buffers with
bp->b_relse(), which adds a hold count and call the release function
when the hold count drops to zero. The b_relse function is supposed
to unlock the buffer by calling xfs_buf_relse() again.
Unfortunately, the superblock buffer is special - the hold count on
it never drops to zero until very late in the unmont process because
it is managed by the filesystem. Hence the bp->b_relse function is
never called, and hence the buffer is never unlocked in this case.
Hence future attempts to access it hang.
I'll need to think about this one for a bit...
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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