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md: factor out a helper to wake up md_thread directly

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md_wakeup_thread() can't wakeup md_thread->tsk if md_thread->run is
still in progress, and in some cases md_thread->tsk need to be woke up
directly, like md_set_readonly() and do_md_stop().

Commit 9dfbdafda3 ("md: unlock mddev before reap sync_thread in
action_store") introduce a new scenario where unregister sync_thread is
not protected by 'reconfig_mutex', this can cause null-ptr-deference in
theroy:

t1: md_set_readonly		t2: action_store
				md_unregister_thread
				// 'reconfig_mutex' is not held
// 'reconfig_mutex' is held by caller
if (mddev->sync_thread)
				 thread = *threadp
				 *threadp = NULL
 wake_up_process(mddev->sync_thread->tsk)
 // null-ptr-deference

Fix this problem by factoring out a helper to wake up md_thread directly,
so that 'sync_thread' won't be accessed multiple times from the reader
side. This helper also prepare to protect md_thread with rcu.

Noted that later patches is going to fix that unregister sync_thread is
not protected by 'reconfig_mutex' from action_store().

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230523021017.3048783-2-yukuai1@huaweicloud.com
This commit is contained in:
Yu Kuai 2023-05-23 10:10:13 +08:00 committed by Song Liu
parent 3ce94ce5d0
commit e5e9b9cb71
1 changed files with 19 additions and 8 deletions
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27
drivers/md/md.c
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@ -92,6 +92,7 @@ static int remove_and_add_spares(struct mddev *mddev,
struct md_rdev *this);
static void mddev_detach(struct mddev *mddev);
static void export_rdev(struct md_rdev *rdev, struct mddev *mddev);
static void md_wakeup_thread_directly(struct md_thread *thread);
/*
* Default number of read corrections we'll attempt on an rdev
@ -6284,10 +6285,12 @@ static int md_set_readonly(struct mddev *mddev, struct block_device *bdev)
}
if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
set_bit(MD_RECOVERY_INTR, &mddev->recovery);
if (mddev->sync_thread)
/* Thread might be blocked waiting for metadata update
* which will now never happen */
wake_up_process(mddev->sync_thread->tsk);
/*
* Thread might be blocked waiting for metadata update which will now
* never happen
*/
md_wakeup_thread_directly(mddev->sync_thread);
if (mddev->external && test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags))
return -EBUSY;
@ -6348,10 +6351,12 @@ static int do_md_stop(struct mddev *mddev, int mode,
}
if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
set_bit(MD_RECOVERY_INTR, &mddev->recovery);
if (mddev->sync_thread)
/* Thread might be blocked waiting for metadata update
* which will now never happen */
wake_up_process(mddev->sync_thread->tsk);
/*
* Thread might be blocked waiting for metadata update which will now
* never happen
*/
md_wakeup_thread_directly(mddev->sync_thread);
mddev_unlock(mddev);
wait_event(resync_wait, (mddev->sync_thread == NULL &&
@ -7898,6 +7903,12 @@ static int md_thread(void *arg)
return 0;
}
static void md_wakeup_thread_directly(struct md_thread *thread)
{
if (thread)
wake_up_process(thread->tsk);
}
void md_wakeup_thread(struct md_thread *thread)
{
if (thread) {