Re: [PATCH 4.19 114/131] ocfs2: avoid inode removal while nfsd is accessing it

Pavel Machek
2020-07-02T21:17:22Z

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Hi!

> commit 4cd9973f9ff69e37dd0ba2bd6e6423f8179c329a upstream.
>
> Patch series "ocfs2: fix nfsd over ocfs2 issues", v2.
>
> This is a series of patches to fix issues on nfsd over ocfs2. patch 1
> is to avoid inode removed while nfsd access it patch 2 & 3 is to fix a
> panic issue.
>
> This patch (of 4):
>
> When nfsd is getting file dentry using handle or parent dentry of some
> dentry, one cluster lock is used to avoid inode removed from other node,
> but it still could be removed from local node, so use a rw lock to avoid
> this.

This causes locking imbalance:

> @@ -2851,6 +2857,11 @@ int ocfs2_nfs_sync_lock(struct ocfs2_super *osb, int ex)
> if (ocfs2_is_hard_readonly(osb))
> return -EROFS;
>
> + if (ex)
> + down_write(&osb->nfs_sync_rwlock);
> + else
> + down_read(&osb->nfs_sync_rwlock);
> +
> if (ocfs2_mount_local(osb))
> return 0;
>
...
status = ocfs2_cluster_lock(osb, lockres, ex ? LKM_EXMODE :LKM_PRMODE,
0, 0);
...
return status;
}

When ocfs2_nfs_sync_lock() returns error, caller can not know if the
lock was taken or not.

ocfs2_get_dentry() for example will not call ocfs2_nfs_sync_unlock()
if sync_lock() failed, resulting in lock imbalance if
ocfs2_cluster_lock() fails.

(Totally untested).

Signed-off-by: Pavel Machek (CIP) <pavel@denx.de>

Best regards,
Pavel

diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index c141b06811a6..8149fb6f1f0d 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -2867,9 +2867,15 @@ int ocfs2_nfs_sync_lock(struct ocfs2_super *osb, int ex)

status = ocfs2_cluster_lock(osb, lockres, ex ? LKM_EXMODE : LKM_PRMODE,
0, 0);
- if (status < 0)
+ if (status < 0) {
mlog(ML_ERROR, "lock on nfs sync lock failed %d\n", status);

+ if (ex)
+ up_write(&osb->nfs_sync_rwlock);
+ else
+ up_read(&osb->nfs_sync_rwlock);
+ }
+
return status;
}

Best regards,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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