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

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Date:   Thu, 2 Jul 2020 23:17:17 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Junxiao Bi <junxiao.bi@...cle.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Changwei Ge <gechangwei@...e.cn>, Gang He <ghe@...e.com>,
        Joel Becker <jlbec@...lplan.org>,
        Jun Piao <piaojun@...wei.com>, Mark Fasheh <mark@...heh.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 4.19 114/131] ocfs2: avoid inode removal while nfsd is
 accessing it

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@...x.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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