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Commit 7286b31e authored by Steven Whitehouse's avatar Steven Whitehouse
Browse files

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: default avatarSteven Whitehouse <swhiteho@redhat.com>
Reported-by: default avatarDavid Teigland <teigland@redhat.com>
Tested-by: default avatarDavid Teigland <teigland@redhat.com>
parent 7c0ef28a

fs/gfs2/glock.c

+5 −7
Original line number Diff line number Diff line
@@ -1488,7 +1488,7 @@ static void examine_bucket(glock_examiner examiner, const struct gfs2_sbd *sdp, 


	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();
@@ -1508,19 +1508,18 @@ static void glock_hash_walk(glock_examiner examiner, const struct gfs2_sbd *sdp) 
 * 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);

	}

}



/**

 * clear_glock - look at a glock and see if we can free it from glock cache
@@ -1536,7 +1535,6 @@ static void clear_glock(struct gfs2_glock *gl) 
	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);

}