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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>
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7c0ef28a2c
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7286b31eab
1 changed files with 5 additions and 7 deletions
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@ -1488,7 +1488,7 @@ static void examine_bucket(glock_examiner examiner, const struct gfs2_sbd *sdp,
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rcu_read_lock();
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hlist_bl_for_each_entry_rcu(gl, pos, head, gl_list) {
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if ((gl->gl_sbd == sdp) && atomic_read(&gl->gl_ref))
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if ((gl->gl_sbd == sdp) && atomic_inc_not_zero(&gl->gl_ref))
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examiner(gl);
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}
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rcu_read_unlock();
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@ -1508,18 +1508,17 @@ static void glock_hash_walk(glock_examiner examiner, const struct gfs2_sbd *sdp)
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* thaw_glock - thaw out a glock which has an unprocessed reply waiting
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* @gl: The glock to thaw
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*
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* N.B. When we freeze a glock, we leave a ref to the glock outstanding,
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* so this has to result in the ref count being dropped by one.
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*/
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static void thaw_glock(struct gfs2_glock *gl)
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{
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if (!test_and_clear_bit(GLF_FROZEN, &gl->gl_flags))
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return;
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goto out;
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set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
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gfs2_glock_hold(gl);
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if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
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if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0) {
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out:
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gfs2_glock_put(gl);
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}
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}
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/**
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@ -1536,7 +1535,6 @@ static void clear_glock(struct gfs2_glock *gl)
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if (gl->gl_state != LM_ST_UNLOCKED)
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handle_callback(gl, LM_ST_UNLOCKED, 0, false);
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spin_unlock(&gl->gl_spin);
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gfs2_glock_hold(gl);
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if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
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gfs2_glock_put(gl);
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}
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