Re: [PATCH v2 1/3] md-cluster: fix error handling and superblock update in update_size revert

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Guaranteed self-deadlock and potential double-unlocks in `update_size` due to calling `md_update_sb()` while the cluster communication lock is held.
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commit bae2db67348747b3864a225bb7b24be69937b7a2
Author: Cao Guanghui <[email protected]>

md-cluster: fix error handling and superblock update in update_size revert

This commit addresses error handling and metadata updates when reverting an
array resize operation in a cluster. It checks the return value of resize()
and updates the superblock to match the in-memory array size.

> diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
> index 24dac6f09da82..9f404660a1fb7 100644
> --- a/drivers/md/md-cluster.c
> +++ b/drivers/md/md-cluster.c
> @@ -1349,6 +1349,10 @@ static void update_size(struct mddev *mddev, sector_t old_dev_sectors)
>  	} else {
>  		/* revert to previous sectors */
>  		ret = mddev->pers->resize(mddev, old_dev_sectors);
> +		if (ret)
> +			pr_err("%s:%d: failed to revert array size\n",
> +			       __func__, __LINE__);
> +		md_update_sb(mddev, 1);

[Severity: High]
Does this call to md_update_sb() cause a self-deadlock?

At this point in update_size(), the cluster communication lock
(MD_CLUSTER_SEND_LOCK) is already held via lock_comm(). When md_update_sb()
is called, it enters mddev->cluster_ops->metadata_update_start(mddev), which
waits for MD_CLUSTER_SEND_LOCK to be cleared. Since the lock is held by the
same thread, this appears to result in a strict self-deadlock during a failed
array resize operation.

Additionally, if the deadlock could somehow be bypassed, md_update_sb() would
complete by calling metadata_update_finish(), which prematurely calls
unlock_comm(), leading to a fatal double-unlock when update_size() later
attempts to call unlock_comm() itself.

>  		ret = __sendmsg(cinfo, &cmsg);
>  		if (ret)
>  			pr_err("%s:%d: failed to send METADATA_UPDATED msg\n",

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Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1