zfsonlinux/zfs — pull request #1981 by behlendorf (2013-12-17 18:29:48+00:00)
Title: 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
Signed-off-by: Brian Behlendorf
Issue #1962