[PATCH 7/7] jbd2: make the whole kjournald2 kthread NOFS safe

[Michal Hocko]

From: Michal Hocko <mhocko@xxxxxxxx>

kjournald2 is central to the transaction commit processing. As such any
potential allocation from this kernel thread has to be GFP_NOFS. Make
sure to mark the whole kernel thread GFP_NOFS by the memalloc_nofs_save.

Suggested-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 fs/jbd2/journal.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index a1a359bfcc9c..78433ce1db40 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -43,6 +43,7 @@
 #include <linux/backing-dev.h>
 #include <linux/bitops.h>
 #include <linux/ratelimit.h>
+#include <linux/sched/mm.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/jbd2.h>
@@ -206,6 +207,13 @@ static int kjournald2(void *arg)
 	wake_up(&journal->j_wait_done_commit);
 
 	/*
+	 * Make sure that no allocations from this kernel thread will ever recurse
+	 * to the fs layer because we are responsible for the transaction commit
+	 * and any fs involvement might get stuck waiting for the trasn. commit.
+	 */
+	memalloc_nofs_save();
+
+	/*
 	 * And now, wait forever for commit wakeup events.
 	 */
 	write_lock(&journal->j_state_lock);
-- 
2.11.0