From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay1.corp.sgi.com [137.38.102.111]) by oss.sgi.com (Postfix) with ESMTP id DBFEF7F3F for ; Wed, 17 Jul 2013 21:25:04 -0500 (CDT) Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by relay1.corp.sgi.com (Postfix) with ESMTP id C95368F8039 for ; Wed, 17 Jul 2013 19:25:01 -0700 (PDT) Received: from ipmail06.adl6.internode.on.net (ipmail06.adl6.internode.on.net [150.101.137.145]) by cuda.sgi.com with ESMTP id Ysyd5ESAIHtBy6YS for ; Wed, 17 Jul 2013 19:24:56 -0700 (PDT) Date: Thu, 18 Jul 2013 12:24:51 +1000 From: Dave Chinner Subject: Re: [PATCH] xfs: Fix a deadlock in xfs_log_commit_cil() code path Message-ID: <20130718022451.GM11674@dastard> References: <1373928754.20769.41.camel@chandra-dt.ibm.com> <20130716005455.GC3920@dastard> <1374096775.8941.3.camel@chandra-dt.ibm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1374096775.8941.3.camel@chandra-dt.ibm.com> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Chandra Seetharaman Cc: XFS mailing list On Wed, Jul 17, 2013 at 04:32:55PM -0500, Chandra Seetharaman wrote: > On Tue, 2013-07-16 at 10:54 +1000, Dave Chinner wrote: > > On Mon, Jul 15, 2013 at 05:52:34PM -0500, Chandra Seetharaman wrote: > > > While testing and rearranging my pquota/gquota code, I stumbled > > > on a xfs_shutdown() during a mount. But the mount just hung. > > > > > > I debugged and found that there is a deadlock involving > > > &log->l_cilp->xc_ctx_lock. > > > > > > It is in a code path where &log->l_cilp->xc_ctx_lock is first > > > acquired in read mode and some levels down the same semaphore > > > is being acquired in write mode causing a deadlock. > > > > > > This is the stack: > > > xfs_log_commit_cil -> acquires &log->l_cilp->xc_ctx_lock in read mode > > > xlog_print_tic_res > > > xfs_force_shutdown > > > xfs_log_force_umount > > > xlog_cil_force > > > xlog_cil_force_lsn > > > xlog_cil_push_foreground > > > xlog_cil_push - tries to acquire same semaphore in write mode > > > > > > This patch fixes the deadlock by not calling xfs_force_shutdown() while > > > holding the semaphore, instead calling it after dropping teh semaphore. > > > > > > Thanks to Dave for suggesting this solution. > > > > > > Signed-off-by: Chandra Seetharaman > > > > > > --- > > > fs/xfs/xfs_log.c | 6 +++--- > > > fs/xfs/xfs_log_cil.c | 10 ++++++---- > > > fs/xfs/xfs_log_priv.h | 2 +- > > > fs/xfs/xfs_trans.c | 2 +- > > > 4 files changed, 11 insertions(+), 9 deletions(-) > > > > > > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c > > > index d852a2b..b9fa2da 100644 > > > --- a/fs/xfs/xfs_log.c > > > +++ b/fs/xfs/xfs_log.c > > > @@ -1837,7 +1837,7 @@ xlog_state_finish_copy( > > > * print out info relating to regions written which consume > > > * the reservation > > > */ > > > -void > > > +int > > > xlog_print_tic_res( > > > struct xfs_mount *mp, > > > struct xlog_ticket *ticket) > > > @@ -1941,7 +1941,7 @@ xlog_print_tic_res( > > > > > > xfs_alert_tag(mp, XFS_PTAG_LOGRES, > > > "xlog_write: reservation ran out. Need to up reservation"); > > > - xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE); > > > + return EFSCORRUPTED; > > > > Note the "SHUTDOWN_CORRUPT_INCORE" reason given here.... > > > > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > > > index 35a2299..d96022f 100644 > > > --- a/fs/xfs/xfs_trans.c > > > +++ b/fs/xfs/xfs_trans.c > > > @@ -1547,7 +1547,7 @@ xfs_trans_commit( > > > xfs_trans_apply_dquot_deltas(tp); > > > > > > error = xfs_log_commit_cil(mp, tp, &commit_lsn, flags); > > > - if (error == ENOMEM) { > > > + if (error) { > > > xfs_force_shutdown(mp, SHUTDOWN_LOG_IO_ERROR); > > > > Which is different to the reason given here. The shutdown reason > > should be maintained for this particular error.... > > I see. What I mean is that the code in xfs_trans_commit() should do something like: if (error) { int reason = SHUTDOWN_LOG_IO_ERROR; if (error == EFSCORRUPTED) reason = SHUTDOWN_CORRUPT_INCORE; xfs_force_shutdown(mp, reason); .... } > > Is it ok if the error reason is not propagated to the xlog_write() code > path ? No - if we get a transaction overflow, we need to trigger a shutdown. That means the error needs to be caught by the xlog_write() path an the filesystem shut down. Looking at it more deeply, you could probably just change the shutdown in xlog_print_tic_res() to use SHUTDOWN_LOG_IO_ERROR and the problem is solved as the shutdown won't try to force the log. i.e. this whole problem will go away with that one line fix... Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs