From 6fc45b6ed921dc00dfb264dc08c7d67ee63d2656 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Fri, 17 Nov 2023 18:21:14 +0100
Subject: [PATCH] dm-delay: fix a race between delay_presuspend and delay_bio
Git-commit: 6fc45b6ed921dc00dfb264dc08c7d67ee63d2656
Patch-mainline: v6.7-rc2
References: git-fixes
In delay_presuspend, we set the atomic variable may_delay and then stop
the timer and flush pending bios. The intention here is to prevent the
delay target from re-arming the timer again.
However, this test is racy. Suppose that one thread goes to delay_bio,
sees that dc->may_delay is one and proceeds; now, another thread executes
delay_presuspend, it sets dc->may_delay to zero, deletes the timer and
flushes pending bios. Then, the first thread continues and adds the bio to
delayed->list despite the fact that dc->may_delay is false.
Fix this bug by changing may_delay's type from atomic_t to bool and
only access it while holding the delayed_bios_lock mutex. Note that we
don't have to grab the mutex in delay_resume because there are no bios
in flight at this point.
(Coly Li: rebased for Linux 5.14 based SUSE kernel)
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Coly Li <colyli@suse.de>
---
drivers/md/dm-delay.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
--- a/drivers/md/dm-delay.c
+++ b/drivers/md/dm-delay.c
@@ -30,7 +30,7 @@ struct delay_c {
struct workqueue_struct *kdelayd_wq;
struct work_struct flush_expired_bios;
struct list_head delayed_bios;
- atomic_t may_delay;
+ bool may_delay;
struct delay_class read;
struct delay_class write;
@@ -191,7 +191,7 @@ static int delay_ctr(struct dm_target *t
INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
INIT_LIST_HEAD(&dc->delayed_bios);
mutex_init(&dc->timer_lock);
- atomic_set(&dc->may_delay, 1);
+ dc->may_delay = true;
dc->argc = argc;
ret = delay_class_ctr(ti, &dc->read, argv);
@@ -246,7 +246,7 @@ static int delay_bio(struct delay_c *dc,
struct dm_delay_info *delayed;
unsigned long expires = 0;
- if (!c->delay || !atomic_read(&dc->may_delay))
+ if (!c->delay)
return DM_MAPIO_REMAPPED;
delayed = dm_per_bio_data(bio, sizeof(struct dm_delay_info));
@@ -255,6 +255,10 @@ static int delay_bio(struct delay_c *dc,
delayed->expires = expires = jiffies + msecs_to_jiffies(c->delay);
mutex_lock(&delayed_bios_lock);
+ if (unlikely(!dc->may_delay)) {
+ mutex_unlock(&delayed_bios_lock);
+ return DM_MAPIO_REMAPPED;
+ }
c->ops++;
list_add_tail(&delayed->list, &dc->delayed_bios);
mutex_unlock(&delayed_bios_lock);
@@ -268,7 +272,9 @@ static void delay_presuspend(struct dm_t
{
struct delay_c *dc = ti->private;
- atomic_set(&dc->may_delay, 0);
+ mutex_lock(&delayed_bios_lock);
+ dc->may_delay = false;
+ mutex_unlock(&delayed_bios_lock);
del_timer_sync(&dc->delay_timer);
flush_bios(flush_delayed_bios(dc, 1));
}
@@ -277,7 +283,7 @@ static void delay_resume(struct dm_targe
{
struct delay_c *dc = ti->private;
- atomic_set(&dc->may_delay, 1);
+ dc->may_delay = true;
}
static int delay_map(struct dm_target *ti, struct bio *bio)