[PATCH] nilfs2: Avoid having an active sc_timer before freeing sci

[Ryusuke Konishi <konishi.ryusuke@gmail.com>]

From: Edward Adam Davis <eadavis@qq.com>

Because kthread_stop did not stop sc_task properly and returned -EINTR,
the sc_timer was not properly closed, ultimately causing the problem [1]
reported by syzbot when freeing sci due to the sc_timer not being closed.

Because the thread sc_task main function nilfs_segctor_thread() returns 0
when it succeeds, when the return value of kthread_stop() is not 0 in
nilfs_segctor_destroy(), we believe that it has not properly closed
sc_timer.
We use timer_shutdown_sync() to sync wait for sc_timer to shutdown, and set
the value of sc_task to NULL under the protection of lock sc_state_lock,
so as to avoid the issue caused by sc_timer not being properly shutdowned.

[1]
ODEBUG: free active (active state 0) object: 00000000dacb411a object type: timer_list hint: nilfs_construction_timeout
Call trace:
 nilfs_segctor_destroy fs/nilfs2/segment.c:2811 [inline]
 nilfs_detach_log_writer+0x668/0x8cc fs/nilfs2/segment.c:2877
 nilfs_put_super+0x4c/0x12c fs/nilfs2/super.c:509

Reported-by: syzbot+24d8b70f039151f65590@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=24d8b70f039151f65590
Tested-by: syzbot+24d8b70f039151f65590@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Fixes: 3f66cc261ccb ("nilfs2: use kthread_create and kthread_stop for the log writer thread")
Cc: <stable@vger.kernel.org> # 6.12+
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
---
Hi Andrew,

Please apply this patch as a bug fix.  It addresses a recently reported
issue by syzbot, where a timer might not be properly shut down.

Thanks,
Ryusuke Konishi

 fs/nilfs2/segment.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index f15ca6fc400d..deee16bc9d4e 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -2768,7 +2768,12 @@ static void nilfs_segctor_destroy(struct nilfs_sc_info *sci)
 
 	if (sci->sc_task) {
 		wake_up(&sci->sc_wait_daemon);
-		kthread_stop(sci->sc_task);
+		if (kthread_stop(sci->sc_task)) {
+			spin_lock(&sci->sc_state_lock);
+			sci->sc_task = NULL;
+			timer_shutdown_sync(&sci->sc_timer);
+			spin_unlock(&sci->sc_state_lock);
+		}
 	}
 
 	spin_lock(&sci->sc_state_lock);
-- 
2.43.0