In zfs_ioc_log_history() function the tsd_set() function is called
with NULL which causes the zfs_allow_log_destroy() to be run. In
this case the passed value will be NULL. This is normally entirely
safe because strfree() maps directly to kfree() which may be passed
a NULL. However, since alternate implementations of strfree() may
not handle this gracefully add a check for NULL.
Observed under an embedded Linux 2.6.32.41 kernel running the
automated testing while running the ZFS Test Suite.
Signed-off-by: caoxuewen <cao.xuewen@zte.com.cn>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#4872
9f3d1407dc