GFS2: Take glock reference in examine_bucket()
We need to check the glock ref counter in a race free way
in order to ensure that the gfs2_glock_hold() call will
succeed. The easiest way to do that is to simply take the
reference count early in the common code of examine_bucket,
skipping any glocks with zero ref count.
That means that the examiner functions all need to put their
reference on the glock once they've performed their function.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Reported-by: David Teigland <teigland@redhat.com>
Tested-by: David Teigland <teigland@redhat.com>
diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 544a809..ce7078d 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1488,7 +1488,7 @@
rcu_read_lock();
hlist_bl_for_each_entry_rcu(gl, pos, head, gl_list) {
- if ((gl->gl_sbd == sdp) && atomic_read(&gl->gl_ref))
+ if ((gl->gl_sbd == sdp) && atomic_inc_not_zero(&gl->gl_ref))
examiner(gl);
}
rcu_read_unlock();
@@ -1508,18 +1508,17 @@
* thaw_glock - thaw out a glock which has an unprocessed reply waiting
* @gl: The glock to thaw
*
- * N.B. When we freeze a glock, we leave a ref to the glock outstanding,
- * so this has to result in the ref count being dropped by one.
*/
static void thaw_glock(struct gfs2_glock *gl)
{
if (!test_and_clear_bit(GLF_FROZEN, &gl->gl_flags))
- return;
+ goto out;
set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
- gfs2_glock_hold(gl);
- if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
+ if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0) {
+out:
gfs2_glock_put(gl);
+ }
}
/**
@@ -1536,7 +1535,6 @@
if (gl->gl_state != LM_ST_UNLOCKED)
handle_callback(gl, LM_ST_UNLOCKED, 0, false);
spin_unlock(&gl->gl_spin);
- gfs2_glock_hold(gl);
if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
gfs2_glock_put(gl);
}