From 6fa7aa50b2c48400bbd045daf3a2498882eb0596 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 28 Oct 2016 12:58:12 -0400 Subject: fs/jbd2, locking/mutex, sched/wait: Use mutex_lock_io() for journal->j_checkpoint_mutex When an ext4 fs is bogged down by a lot of metadata IOs (in the reported case, it was deletion of millions of files, but any massive amount of journal writes would do), after the journal is filled up, tasks which try to access the filesystem and aren't currently performing the journal writes end up waiting in __jbd2_log_wait_for_space() for journal->j_checkpoint_mutex. Because those mutex sleeps aren't marked as iowait, this condition can lead to misleadingly low iowait and /proc/stat:procs_blocked. While iowait propagation is far from strict, this condition can be triggered fairly easily and annotating these sleeps correctly helps initial diagnosis quite a bit. Use the new mutex_lock_io() for journal->j_checkpoint_mutex so that these sleeps are properly marked as iowait. Reported-by: Mingbo Wan Signed-off-by: Tejun Heo Signed-off-by: Peter Zijlstra (Intel) Cc: Andreas Dilger Cc: Andrew Morton Cc: Jan Kara Cc: Jens Axboe Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Theodore Ts'o Cc: Thomas Gleixner Cc: kernel-team@fb.com Link: http://lkml.kernel.org/r/1477673892-28940-5-git-send-email-tj@kernel.org Signed-off-by: Ingo Molnar --- fs/jbd2/commit.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/jbd2/commit.c') diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c index 8c514367ba5a..b6b194ec1b4f 100644 --- a/fs/jbd2/commit.c +++ b/fs/jbd2/commit.c @@ -393,7 +393,7 @@ void jbd2_journal_commit_transaction(journal_t *journal) /* Do we need to erase the effects of a prior jbd2_journal_flush? */ if (journal->j_flags & JBD2_FLUSHED) { jbd_debug(3, "super block updated\n"); - mutex_lock(&journal->j_checkpoint_mutex); + mutex_lock_io(&journal->j_checkpoint_mutex); /* * We hold j_checkpoint_mutex so tail cannot change under us. * We don't need any special data guarantees for writing sb -- cgit v1.2.3