Re: [PATCH v3 1/4] md/raid5: Hide the origin mddev->thread before takeover

[yu kuai]

Hi,

在 2026/9/23 19:21, Zhihao Cheng 写道:
> The raid5 takeover invokes setup_conf and allocates strip heads, but
> it wakes up the wrong thread, which lefts strip heads in the list
> 'conf->released_stripes' and not being processed. If raid5_run fails,
> the strip heads won't be released, which triggers the following slab
> warnings (CONFIG_SLUB_DEBUG):
>   BUG raid5-md0 (Not tainted): Objects remaining on __kmem_cache_shutdown()
>   Object 0x0000000062fad548 @offset=3968
>   Object 0x000000007f74683c @offset=4960
>   WARNING: mm/slub.c:1268 at __slab_err+0x31/0x40, CPU#0: bash/865
>   RIP: 0010:__slab_err+0x31
>   Call Trace:
>    __kmem_cache_shutdown.cold+0x15b
>    kmem_cache_destroy+0x71
>    free_conf+0xf8
>    raid5_run.cold+0x463
>    level_store+0x64e
>    md_attr_store+0xd7

Is this still a problem with following patch?

[PATCH] md/raid5: drain released_stripes before destroying the cache - 
Li Youhong 
<https://lore.kernel.org/all/20260929083916.50620-1-dayou5941@xxxxxxx/>

>
> The detailed triggering process is as follows:
>   mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda /dev/sdb
>   --force --assume-clean # create raid1, mddev->thread is raid1d
>   echo 5 > /sys/block/md0/md/level
>    level_store
>     raid5_takeover_raid1
>       setup_conf
>        grow_stripes
>         grow_one_stripe
>          sh = alloc_stripe
>          raid5_release_stripe
>            md_wakeup_thread(conf->mddev->thread) // wakeup raid1d
>       raid5_run
>        ENOMEM = raid5_create_ctx_pool
>        free_conf
>         shrink_stripes
>          drop_one_stripe // no strips found from the conf->inactive_list
>          kmem_cache_destroy(conf->slab_cache)
> 	 __kmem_cache_shutdown
> 	  free_partial
> 	   list_slab_objects // some entries are not released !
>
> Fix it by hiding the origin mddev->thread before takeover, so that
> new allocating strip heads can be put into 'conf->inactive_list',
> which can be found by drop_one_stripe().
>
> Fixes: 773ca82fa1ee ("raid5: make release_stripe lockless")
> Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
> ---
>   drivers/md/raid5.c | 37 ++++++++++++++++++++++++++++---------
>   1 file changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index c091bba95c31..7e87e8a60f5f 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -9039,19 +9039,38 @@ static void *raid5_takeover(struct mddev *mddev)
>   	 *  raid4 - trivial - just use a raid4 layout.
>   	 *  raid6 - Providing it is a *_6 layout
>   	 */
> -	if (mddev->level == 0)
> -		return raid45_takeover_raid0(mddev, 5);
> -	if (mddev->level == 1)
> -		return raid5_takeover_raid1(mddev);
> -	if (mddev->level == 4) {
> +	void *ret = ERR_PTR(-EINVAL);
> +	struct md_thread *thread;
> +
> +	thread = rcu_dereference_protected(mddev->thread,
> +				lockdep_is_held(&mddev->reconfig_mutex));
> +	/*
> +	 * Set mddev->thread to NULL before setup_conf() to avoid waking up
> +	 * wrong thread(eg. raid1), which can prevent the strips from being
> +	 * left unreleased in the error handling path(free_conf) of raid5_run.
> +	 */
> +	rcu_assign_pointer(mddev->thread, NULL);
> +
> +	switch (mddev->level) {
> +	case 0:
> +		ret = raid45_takeover_raid0(mddev, 5);
> +		break;
> +	case 1:
> +		ret = raid5_takeover_raid1(mddev);
> +		break;
> +	case 4:
>   		mddev->new_layout = ALGORITHM_PARITY_N;
>   		mddev->new_level = 5;
> -		return setup_conf(mddev);
> +		ret = setup_conf(mddev);
> +		break;
> +	case 6:
> +		ret = raid5_takeover_raid6(mddev);
> +		break;
>   	}
> -	if (mddev->level == 6)
> -		return raid5_takeover_raid6(mddev);
>   
> -	return ERR_PTR(-EINVAL);
> +	rcu_assign_pointer(mddev->thread, thread);
> +
> +	return ret;
>   }
>   
>   static void *raid4_takeover(struct mddev *mddev)

-- 
Thanks,
Kuai