[PATCH] block: Prevent hung_check firing during long sync IO

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

submit_bio_wait() can be called from ioctl(BLKSECDISCARD), which
may take long time to complete, as Salman mentioned, 4K BLKSECDISCARD
takes up to 100 second on some devices. Also any block I/O operation
that occurs after the BLKSECDISCARD is submitted will also potentially
be affected by the hung task timeouts.

So prevent hung_check from firing by taking same approach used
in blk_execute_rq(), and the wake-up interval is set as half the
hung_check timer period, which keeps overhead low enough.

Cc: Salman Qazi <sqazi@google.com>
Cc: Jesse Barnes <jsbarnes@google.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Link: https://lkml.org/lkml/2020/2/12/1193
Reported-by: Salman Qazi <sqazi@google.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/bio.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 94d697217887..c9ce19a86de7 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -17,6 +17,7 @@
 #include <linux/cgroup.h>
 #include <linux/blk-cgroup.h>
 #include <linux/highmem.h>
+#include <linux/sched/sysctl.h>
 
 #include <trace/events/block.h>
 #include "blk.h"
@@ -1019,12 +1020,19 @@ 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;
 
 	bio->bi_private = &done;
 	bio->bi_end_io = submit_bio_wait_endio;
 	bio->bi_opf |= REQ_SYNC;
 	submit_bio(bio);
-	wait_for_completion_io(&done);
+
+	/* 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)));
+	else
+		wait_for_completion_io(&done);
 
 	return blk_status_to_errno(bio->bi_status);
 }
-- 
2.20.1