On Tue, Apr 29, 2014 at 08:18:49AM +1000, Dave Chinner wrote:
> On Mon, Apr 28, 2014 at 04:39:50PM -0500, Mark Tinguely wrote:
> > On 04/28/14 15:54, Dave Chinner wrote:
> > >On Mon, Apr 28, 2014 at 11:35:16AM -0500, Eric Sandeen wrote:
...
>
> xfs: don't sleep in xlog_cil_force_lsn on shutdown
>
> 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.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> 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);
>
Why is this necessary? It looks like xlog_state_do_callback() will hit
the xlog_cil_committed() callback with the aborted flag...
> #ifdef XFSERRORDEBUG
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 7e54553..3a68ddf 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -385,7 +385,15 @@ xlog_cil_committed(
> xfs_extent_busy_clear(mp, &ctx->busy_extents,
> (mp->m_flags & XFS_MOUNT_DISCARD) && !abort);
>
> + /*
> + * If we are aborting the commit, wake up anyone waiting on the
> + * committing list. If we don't, then a shutdown we can leave processes
> + * waiting in xlog_cil_force_lsn() waiting on a sequence commit that
> + * will never happen because we aborted it.
> + */
> spin_lock(&ctx->cil->xc_push_lock);
> + if (abort)
> + wake_up_all(&cil->xc_commit_wait);
There's a compile error here. The parameter should be '&ctx->cil->...'
Brian
> list_del(&ctx->committing);
> spin_unlock(&ctx->cil->xc_push_lock);
>
> @@ -564,8 +572,18 @@ restart:
> spin_lock(&cil->xc_push_lock);
> list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
> /*
> + * Avoid getting stuck in this loop because we were woken by the
> + * shutdown, but then went back to sleep once already in the
> + * shutdown state.
> + */
> + if (XLOG_FORCED_SHUTDOWN(log)) {
> + spin_unlock(&cil->xc_push_lock);
> + goto out_abort_free_ticket;
> + }
> +
> + /*
> * Higher sequences will wait for this one so skip them.
> - * Don't wait for own own sequence, either.
> + * Don't wait for our own sequence, either.
> */
> if (new_ctx->sequence >= ctx->sequence)
> continue;
> @@ -810,6 +828,13 @@ restart:
> */
> spin_lock(&cil->xc_push_lock);
> list_for_each_entry(ctx, &cil->xc_committing, committing) {
> + /*
> + * Avoid getting stuck in this loop because we were woken by the
> + * shutdown, but then went back to sleep once already in the
> + * shutdown state.
> + */
> + if (XLOG_FORCED_SHUTDOWN(log))
> + goto out_shutdown;
> if (ctx->sequence > sequence)
> continue;
> if (!ctx->commit_lsn) {
> @@ -833,14 +858,12 @@ restart:
> * push sequence after the above wait loop and the CIL still contains
> * dirty objects.
> *
> - * When the push occurs, it will empty the CIL and
> - * atomically increment the currect sequence past the push sequence and
> - * move it into the committing list. Of course, if the CIL is clean at
> - * the time of the push, it won't have pushed the CIL at all, so in that
> - * case we should try the push for this sequence again from the start
> - * just in case.
> + * When the push occurs, it will empty the CIL and atomically increment
> + * the currect sequence past the push sequence and move it into the
> + * committing list. Of course, if the CIL is clean at the time of the
> + * push, it won't have pushed the CIL at all, so in that case we should
> + * try the push for this sequence again from the start just in case.
> */
> -
> if (sequence == cil->xc_current_sequence &&
> !list_empty(&cil->xc_cil)) {
> spin_unlock(&cil->xc_push_lock);
> @@ -849,6 +872,17 @@ restart:
>
> spin_unlock(&cil->xc_push_lock);
> return commit_lsn;
> +
> + /*
> + * We detected a shutdown in progress. We need to trigger the log force
> + * to pass through it's iclog state machine error handling, even though
> + * we are already in a shutdown state. Hence we can't return
> + * NULLCOMMITLSN here as that has special meaning to log forces (i.e.
> + * LSN is already stable), so we return a zero LSN instead.
> + */
> +out_shutdown:
> + spin_unlock(&cil->xc_push_lock);
> + return 0;
> }
>
> /*
>
> _______________________________________________
> xfs mailing list
> xfs@xxxxxxxxxxx
> http://oss.sgi.com/mailman/listinfo/xfs
_______________________________________________
xfs mailing list
xfs@xxxxxxxxxxx
http://oss.sgi.com/mailman/listinfo/xfs
