Hi Dave, Do you plan to post a patch for the bug you discovered in xfs_iflush() to goto abort_out when xfs_imap_to_bp() fails? We can include this patch & see we can hit a recreate of this issue. Thanks. --Shyam -----Original Message----- From: Dave Chinner [mailto:david@xxxxxxxxxxxxx] Sent: 11 April 2016 06:51 To: Alex Lyakas Cc: Shyam Kaushik; Brian Foster; xfs@xxxxxxxxxxx Subject: Re: XFS hung task in xfs_ail_push_all_sync() when unmounting FS after disk failure/recovery On Sun, Apr 10, 2016 at 09:40:29PM +0300, Alex Lyakas wrote: > Hello Dave, > > On Sat, Apr 9, 2016 at 1:46 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > On Fri, Apr 08, 2016 at 04:21:02PM +0530, Shyam Kaushik wrote: > >> Hi Dave, Brian, Carlos, > >> > >> While trying to reproduce this issue I have been running into different > >> issues that are similar. Underlying issue remains the same when backend to > >> XFS is failed & we unmount XFS, we run into hung-task timeout (180-secs) > >> with stack like > >> > >> kernel: [14952.671131] [<ffffffffc06a5f59>] > >> xfs_ail_push_all_sync+0xa9/0xe0 [xfs] > >> kernel: [14952.671139] [<ffffffff810b26b0>] ? > >> prepare_to_wait_event+0x110/0x110 > >> kernel: [14952.671181] [<ffffffffc0690111>] xfs_unmountfs+0x61/0x1a0 > >> [xfs] > >> > >> while running trace-events, XFS ail push keeps looping around > >> > >> xfsaild/dm-10-21143 [001] ...2 17878.555133: xfs_ilock_nowait: dev > >> 253:10 ino 0x0 flags ILOCK_SHARED caller xfs_inode_item_push [xfs] > > > > Looks like either a stale inode (which should never reach the AIL) > > or it's an inode that's been reclaimed and this is a use after free > > situation. Given that we are failing IOs here, I'd suggest it's more > > likely to be an IO failure that's caused a writeback problem, not an > > interaction with stale inodes. > > > > So, look at xfs_iflush. If an IO fails, it is supposed to unlock the > > inode by calling xfs_iflush_abort(), which will also remove it from > > the AIL. This can also happen on reclaim of a dirty inode, and if so > > we'll still reclaim the inode because reclaim assumes xfs_iflush() > > cleans up properly. > > > > Which, apparently, it doesn't: > > > > /* > > * Get the buffer containing the on-disk inode. > > */ > > error = xfs_imap_to_bp(mp, NULL, &ip->i_imap, &dip, &bp, XBF_TRYLOCK, 0); > > if (error || !bp) { > > xfs_ifunlock(ip); > > return error; > > } > > > > This looks like a bug - xfs_iflush hasn't aborted the inode > > writeback on failure - it's just unlocked the flush lock. Hence it > > has left the inode dirty in the AIL, and then the inode has probably > > then been reclaimed, setting the inode number to zero. > In our case, we do not reach this call, because XFS is already marked > as "shutdown", so in our case we do: > /* > * This may have been unpinned because the filesystem is shutting > * down forcibly. If that's the case we must not write this inode > * to disk, because the log record didn't make it to disk. > * > * We also have to remove the log item from the AIL in this case, > * as we wait for an empty AIL as part of the unmount process. > */ > if (XFS_FORCED_SHUTDOWN(mp)) { > error = -EIO; > goto abort_out; > } > > So we call xfs_iflush_abort, but due to "iip" being NULL (as Shyam > mentioned earlier in this thread), we proceed directly to > xfs_ifunlock(ip), which now becomes the same situation as you > described above. If you are getting this occuring, something else has already gone wrong as you can't have a dirty inode without a log item attached to it. So it appears to me that you are reporting a symptom of a problem after it has occured, not the root cause. Maybe it is the same root cause, maybe not. Either way, it doesn't help us solve any problem. > The comment clearly says "We also have to remove the log item from the > AIL in this case, as we wait for an empty AIL as part of the unmount > process." Could you perhaps point us at the code that is supposed to > remove the log item from the AIL? Apparently this is not happening. xfs_iflush_abort or xfs_iflush_done does that work. -Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
