From: Chunwei Chen <tuxoko@gmail.com>
Date: Tue, 17 Dec 2013 18:18:25 +0000 (-0800)
Subject: Fix z_sync_cnt decrement in zfs_close
X-Git-Tag: zfs-0.6.3~140
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=7dc71949f2f013a7bf744230d60770893ce23a6a;p=zfs

Fix z_sync_cnt decrement in zfs_close

The comment in zfs_close states that "Under Linux the zfs_close() hook
is not symmetric with zfs_open()". This is not true. zfs_open/zfs_close
is associated with every successful struct file creation/deletion, which
should always be balanced.

Here is an example of what's wrong:

Process A		B
	open(O_SYNC)
	z_sync_cnt = 1
			open(O_SYNC)
			z_sync_cnt = 2
	close()
	z_sync_cnt = 0

So z_sync_cnt is 0 even if B still has the file with O_SYNC.

Also moves the generic_file_open call before zfs_open to ensure that in
the case generic_file_open fails z_sync_cnt is not incremented.  This
is safe because generic_file_open has no side effects.

Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1962
---

diff --git a/module/zfs/zfs_vnops.c b/module/zfs/zfs_vnops.c
index 4a34f055a..8e4694ff6 100644
--- a/module/zfs/zfs_vnops.c
+++ b/module/zfs/zfs_vnops.c
@@ -235,13 +235,9 @@ zfs_close(struct inode *ip, int flag, cred_t *cr)
 	ZFS_ENTER(zsb);
 	ZFS_VERIFY_ZP(zp);
 
-	/*
-	 * Zero the synchronous opens in the znode.  Under Linux the
-	 * zfs_close() hook is not symmetric with zfs_open(), it is
-	 * only called once when the last reference is dropped.
-	 */
+	/* Decrement the synchronous opens in the znode */
 	if (flag & O_SYNC)
-		zp->z_sync_cnt = 0;
+		atomic_dec_32(&zp->z_sync_cnt);
 
 	if (!zfs_has_ctldir(zp) && zsb->z_vscan && S_ISREG(ip->i_mode) &&
 	    !(zp->z_pflags & ZFS_AV_QUARANTINED) && zp->z_size > 0)
diff --git a/module/zfs/zpl_file.c b/module/zfs/zpl_file.c
index 0d46eee02..690f93838 100644
--- a/module/zfs/zpl_file.c
+++ b/module/zfs/zpl_file.c
@@ -36,15 +36,16 @@ zpl_open(struct inode *ip, struct file *filp)
 	cred_t *cr = CRED();
 	int error;
 
+	error = generic_file_open(ip, filp);
+	if (error)
+		return (error);
+
 	crhold(cr);
 	error = -zfs_open(ip, filp->f_mode, filp->f_flags, cr);
 	crfree(cr);
 	ASSERT3S(error, <=, 0);
 
-	if (error)
-		return (error);
-
-	return generic_file_open(ip, filp);
+	return (error);
 }
 
 static int