On Tue, May 06, 2014 at 09:27:46AM -0400, Brian Foster wrote: > On Tue, May 06, 2014 at 11:04:40AM +1000, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > Reports of a shutdown hang when fsyncing a directory have surfaced, > > such as this: > > > > [ 3663.394472] Call Trace: > > [ 3663.397199] [<ffffffff815f1889>] schedule+0x29/0x70 > > [ 3663.402743] [<ffffffffa01feda5>] xlog_cil_force_lsn+0x185/0x1a0 [xfs] > > [ 3663.416249] [<ffffffffa01fd3af>] _xfs_log_force_lsn+0x6f/0x2f0 [xfs] > > [ 3663.429271] [<ffffffffa01a339d>] xfs_dir_fsync+0x7d/0xe0 [xfs] > > [ 3663.435873] [<ffffffff811df8c5>] do_fsync+0x65/0xa0 > > [ 3663.441408] [<ffffffff811dfbc0>] SyS_fsync+0x10/0x20 > > [ 3663.447043] [<ffffffff815fc7d9>] system_call_fastpath+0x16/0x1b > > > > If we trigger a shutdown in xlog_cil_push() from xlog_write(), we > > will never wake waiters on the current push sequence number, so > > anything waiting in xlog_cil_force_lsn() for that push sequence > > number to come up will not get woken and hence stall the shutdown. > > > > Fix this by ensuring we call wake_up_all(&cil->xc_commit_wait) in > > the push abort handling, in the log shutdown code when waking all > > waiters, and adding a shutdown check in the sequence completion wait > > loops to ensure they abort when a wakeup due to a shutdown occurs. > > > > Reported-by: Boris Ranto <branto@xxxxxxxxxx> > > Reported-by: Eric Sandeen <esandeen@xxxxxxxxxx> > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > > --- > > Previously posted here, for reference: > > http://oss.sgi.com/archives/xfs/2014-04/msg00801.html > > > fs/xfs/xfs_log.c | 7 +++++-- > > fs/xfs/xfs_log_cil.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------- > > 2 files changed, 47 insertions(+), 10 deletions(-) > > > > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c > > index a5f8bd9..dbba2d7 100644 > > --- a/fs/xfs/xfs_log.c > > +++ b/fs/xfs/xfs_log.c > > @@ -3952,11 +3952,14 @@ xfs_log_force_umount( > > retval = xlog_state_ioerror(log); > > spin_unlock(&log->l_icloglock); > > } > > + > > /* > > - * Wake up everybody waiting on xfs_log_force. > > - * Callback all log item committed functions as if the > > + * Wake up everybody waiting on xfs_log_force. This needs to wake anyone > > + * waiting on a CIL push that is issued as part of a log force first > > + * before running the log item committed callback functions as if the > > * log writes were completed. > > */ > > + wake_up_all(&log->l_cilp->xc_commit_wait); > > xlog_state_do_callback(log, XFS_LI_ABORTED, NULL); > > > > This looks fine to me with the defensive reasoning described in the > aforementioned link, but it also looks like it could race with a force > and sleep because we don't take xc_push_lock. We take the lock for the > same wake up down in xlog_cil_committed(), so a hang seems unlikely at > this point. We can't really race in any meaningful way- the filesystem and log are already marked as shut down. Hence any new sleeper at this point will detect a shutdown before trying to sleep. Even if we do race, the xlog_cil_committed() will catch any stragglers... > Given that the comment is kind of wordy (and unless we want to do the > locking here as well), could we update the comment to reflect this? > E.g., something like: > > /* > * Wake up everybody waiting on a CIL push and/or log force. Wake the > * CIL push first as if the log writes were completed. The abort > * handling in the log item committed callback functions will do this > * again under lock to avoid races. > */ > > Thoughts? Makes sense. I'll change it. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
