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md: protect md_unregister_thread from reentrancy

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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>
This commit is contained in:
Guoqing Jiang 2022-04-29 16:49:09 +08:00 committed by Song Liu
parent 8b48ec23cc
commit 1e26774228
1 changed files with 10 additions and 5 deletions
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15
drivers/md/md.c
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@ -7963,17 +7963,22 @@ 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);
}