[PATCH 1/2] block: add blk_default_io_timeout() for avoiding task hung in sync IO

[Ming Lei <ming.lei@redhat.com>]

Add helper of blk_default_io_timeout(), so that the two current users
can benefit from it.

Also direct IO users will use it in the following patch, so define the
helper in public header.

Cc: Salman Qazi <sqazi@google.com>
Cc: Jesse Barnes <jsbarnes@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/bio.c            |  9 +++------
 block/blk-exec.c       |  8 +++-----
 include/linux/blkdev.h | 10 ++++++++++
 3 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 21cbaa6a1c20..f67afa159de7 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1069,18 +1069,15 @@ static void submit_bio_wait_endio(struct bio *bio)
 int submit_bio_wait(struct bio *bio)
 {
 	DECLARE_COMPLETION_ONSTACK_MAP(done, bio->bi_disk->lockdep_map);
-	unsigned long hang_check;
+	unsigned long timeout = blk_default_io_timeout();
 
 	bio->bi_private = &done;
 	bio->bi_end_io = submit_bio_wait_endio;
 	bio->bi_opf |= REQ_SYNC;
 	submit_bio(bio);
 
-	/* Prevent hang_check timer from firing at us during very long I/O */
-	hang_check = sysctl_hung_task_timeout_secs;
-	if (hang_check)
-		while (!wait_for_completion_io_timeout(&done,
-					hang_check * (HZ/2)))
+	if (timeout)
+		while (!wait_for_completion_io_timeout(&done, timeout))
 			;
 	else
 		wait_for_completion_io(&done);
diff --git a/block/blk-exec.c b/block/blk-exec.c
index e20a852ae432..17b5cf07e1a3 100644
--- a/block/blk-exec.c
+++ b/block/blk-exec.c
@@ -80,15 +80,13 @@ void blk_execute_rq(struct request_queue *q, struct gendisk *bd_disk,
 		   struct request *rq, int at_head)
 {
 	DECLARE_COMPLETION_ONSTACK(wait);
-	unsigned long hang_check;
+	unsigned long timeout = blk_default_io_timeout();
 
 	rq->end_io_data = &wait;
 	blk_execute_rq_nowait(q, bd_disk, rq, at_head, blk_end_sync_rq);
 
-	/* Prevent hang_check timer from firing at us during very long I/O */
-	hang_check = sysctl_hung_task_timeout_secs;
-	if (hang_check)
-		while (!wait_for_completion_io_timeout(&wait, hang_check * (HZ/2)));
+	if (timeout)
+		while (!wait_for_completion_io_timeout(&wait, timeout));
 	else
 		wait_for_completion_io(&wait);
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f00bd4042295..3d594406b96c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -27,6 +27,7 @@
 #include <linux/percpu-refcount.h>
 #include <linux/scatterlist.h>
 #include <linux/blkzoned.h>
+#include <linux/sched/sysctl.h>
 
 struct module;
 struct scsi_ioctl_command;
@@ -1827,4 +1828,13 @@ static inline void blk_wake_io_task(struct task_struct *waiter)
 		wake_up_process(waiter);
 }
 
+/*
+ * Used in sync IO for avoiding to triger task hung warning, which may
+ * cause system panic or reboot.
+ */
+static inline unsigned long blk_default_io_timeout(void)
+{
+	return sysctl_hung_task_timeout_secs * (HZ / 2);
+}
+
 #endif
-- 
2.25.2