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From:   Nick Huang <nickhuang@synology.com>
To:     bfields@fieldses.org, chuck.lever@oracle.com
Cc:     linux-nfs@vger.kernel.org,
        Yu Hsiang Huang <nickhuang@synology.com>,
        Bing Jing Chang <bingjingc@synology.com>,
        Robbie Ko <robbieko@synology.com>
Subject: [PATCH] nfsd: Prevent truncation of an unlinked inode from blocking access to its directory
Date:   Fri, 14 May 2021 11:58:29 +0800
Message-Id: <20210514035829.5230-1-nickhuang@synology.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Yu Hsiang Huang <nickhuang@synology.com>

Truncation of an unlinked inode may take a long time for I/O waiting, and
it doesn't have to prevent access to the directory. Thus, let truncation
occur outside the directory's mutex, just like do_unlinkat() does.

Signed-off-by: Yu Hsiang Huang <nickhuang@synology.com>
Signed-off-by: Bing Jing Chang <bingjingc@synology.com>
Signed-off-by: Robbie Ko <robbieko@synology.com>
---
 fs/nfsd/vfs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 15adf1f6ab21..39948f130712 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1859,6 +1859,7 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
 {
 	struct dentry	*dentry, *rdentry;
 	struct inode	*dirp;
+	struct inode	*rinode;
 	__be32		err;
 	int		host_err;
 
@@ -1887,6 +1888,8 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
 		host_err = -ENOENT;
 		goto out_drop_write;
 	}
+	rinode = d_inode(rdentry);
+	ihold(rinode);
 
 	if (!type)
 		type = d_inode(rdentry)->i_mode & S_IFMT;
@@ -1902,6 +1905,8 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
 	if (!host_err)
 		host_err = commit_metadata(fhp);
 	dput(rdentry);
+	fh_unlock(fhp);
+	iput(rinode);    /* truncate the inode here */
 
 out_drop_write:
 	fh_drop_write(fhp);
-- 
2.25.1