linux-kernel - [PATCH 5.4 068/320] floppy: Fix hang in watchdog when disk is ejected

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Date:   Mon, 24 Jan 2022 19:40:52 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tasos Sahanidis <tasos@...ossah.com>,
        Denis Efremov <efremov@...ux.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 068/320] floppy: Fix hang in watchdog when disk is ejected

From: Tasos Sahanidis <tasos@...ossah.com>

[ Upstream commit fb48febce7e30baed94dd791e19521abd2c3fd83 ]

When the watchdog detects a disk change, it calls cancel_activity(),
which in turn tries to cancel the fd_timer delayed work.

In the above scenario, fd_timer_fn is set to fd_watchdog(), meaning
it is trying to cancel its own work.
This results in a hang as cancel_delayed_work_sync() is waiting for the
watchdog (itself) to return, which never happens.

This can be reproduced relatively consistently by attempting to read a
broken floppy, and ejecting it while IO is being attempted and retried.

To resolve this, this patch calls cancel_delayed_work() instead, which
cancels the work without waiting for the watchdog to return and finish.

Before this regression was introduced, the code in this section used
del_timer(), and not del_timer_sync() to delete the watchdog timer.

Link: https://lore.kernel.org/r/399e486c-6540-db27-76aa-7a271b061f76@tasossah.com
Fixes: 070ad7e793dc ("floppy: convert to delayed work and single-thread wq")
Signed-off-by: Tasos Sahanidis <tasos@...ossah.com>
Signed-off-by: Denis Efremov <efremov@...ux.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/block/floppy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index ac97a1e2e5ddc..212a1e1ce0d9e 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -1003,7 +1003,7 @@ static DECLARE_DELAYED_WORK(fd_timer, fd_timer_workfn);
 static void cancel_activity(void)
 {
 	do_floppy = NULL;
-	cancel_delayed_work_sync(&fd_timer);
+	cancel_delayed_work(&fd_timer);
 	cancel_work_sync(&floppy_work);
 }

-- 
2.34.1