From 7286b31eaba6404fa92f68d04626da1f395b3916 Mon Sep 17 00:00:00 2001 From: Steven Whitehouse Date: Tue, 20 Aug 2013 09:35:09 +0100 Subject: [PATCH] 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 Reported-by: David Teigland Tested-by: David Teigland --- fs/gfs2/glock.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c index 544a809819c3..ce7078d5aa97 100644 --- a/fs/gfs2/glock.c +++ b/fs/gfs2/glock.c @@ -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(); @@ -1508,18 +1508,17 @@ 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); + } } /** @@ -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); } -- 2.34.1