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 <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Issue #1962

1 files changed, 5 insertions, 4 deletions

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