From d09feb42da01ac0e707000c5a7d215237047877c Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Thu, 5 Sep 2019 17:32:48 -0700 Subject: [PATCH] xfs: fix missed wakeup on l_flush_wait commit cdea5459ce263fbc963657a7736762ae897a8ae6 upstream. The code in xlog_wait uses the spinlock to make adding the task to the wait queue, and setting the task state to UNINTERRUPTIBLE atomic with respect to the waker. Doing the wakeup after releasing the spinlock opens up the following race condition: Task 1 task 2 add task to wait queue wake up task set task state to UNINTERRUPTIBLE This issue was found through code inspection as a result of kworkers being observed stuck in UNINTERRUPTIBLE state with an empty wait queue. It is rare and largely unreproducable. Simply moving the spin_unlock to after the wake_up_all results in the waker not being able to see a task on the waitqueue before it has set its state to UNINTERRUPTIBLE. This bug dates back to the conversion of this code to generic waitqueue infrastructure from a counting semaphore back in 2008 which didn't place the wakeups consistently w.r.t. to the relevant spin locks. [dchinner: Also fix a similar issue in the shutdown path on xc_commit_wait. Update commit log with more details of the issue.] Fixes: d748c62367eb ("[XFS] Convert l_flushsema to a sv_t") Reported-by: Chris Mason Signed-off-by: Rik van Riel Signed-off-by: Dave Chinner Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong Signed-off-by: Joseph Qi Reviewed-by: Xiaoguang Wang --- fs/xfs/xfs_log.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c index 03d942a21bca..ffdc3f58867e 100644 --- a/fs/xfs/xfs_log.c +++ b/fs/xfs/xfs_log.c @@ -2707,7 +2707,6 @@ xlog_state_do_callback( int funcdidcallbacks; /* flag: function did callbacks */ int repeats; /* for issuing console warnings if * looping too many times */ - int wake = 0; spin_lock(&log->l_icloglock); first_iclog = iclog = log->l_iclog; @@ -2909,11 +2908,9 @@ xlog_state_do_callback( #endif if (log->l_iclog->ic_state & (XLOG_STATE_ACTIVE|XLOG_STATE_IOERROR)) - wake = 1; - spin_unlock(&log->l_icloglock); - - if (wake) wake_up_all(&log->l_flush_wait); + + spin_unlock(&log->l_icloglock); } @@ -4021,7 +4018,9 @@ xfs_log_force_umount( * item committed callback functions will do this again under lock to * avoid races. */ + spin_lock(&log->l_cilp->xc_push_lock); wake_up_all(&log->l_cilp->xc_commit_wait); + spin_unlock(&log->l_cilp->xc_push_lock); xlog_state_do_callback(log, XFS_LI_ABORTED, NULL); #ifdef XFSERRORDEBUG -- GitLab