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Subject[PATCH AUTOSEL 5.10 25/38] md: protect md_unregister_thread from reentrancy
Date
From: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>

[ Upstream commit 1e267742283a4b5a8ca65755c44166be27e9aa0f ]

Generally, the md_unregister_thread is called with reconfig_mutex, but
raid_message in dm-raid doesn't hold reconfig_mutex to unregister thread,
so md_unregister_thread can be called simulitaneously from two call sites
in theory.

Then after previous commit which remove the protection of reconfig_mutex
for md_unregister_thread completely, the potential issue could be worse
than before.

Let's take pers_lock at the beginning of function to ensure reentrancy.

Reported-by: Donald Buczek <buczek@molgen.mpg.de>
Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/md/md.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e4e855976dca..f8f24e9de69a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7968,17 +7968,22 @@ EXPORT_SYMBOL(md_register_thread);

void md_unregister_thread(struct md_thread **threadp)
{
- struct md_thread *thread = *threadp;
- if (!thread)
- return;
- pr_debug("interrupting MD-thread pid %d\n", task_pid_nr(thread->tsk));
- /* Locking ensures that mddev_unlock does not wake_up a
+ struct md_thread *thread;
+
+ /*
+ * Locking ensures that mddev_unlock does not wake_up a
* non-existent thread
*/
spin_lock(&pers_lock);
+ thread = *threadp;
+ if (!thread) {
+ spin_unlock(&pers_lock);
+ return;
+ }
*threadp = NULL;
spin_unlock(&pers_lock);

+ pr_debug("interrupting MD-thread pid %d\n", task_pid_nr(thread->tsk));
kthread_stop(thread->tsk);
kfree(thread);
}
--
2.35.1
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