GFS2: Fix race in glock lru glock disposal (94a09a39) · Commits · 戴 / test

We must not leave items on the LRU list with GLF_LOCK set, since they can be removed if the glock is brought back into use, which may then potentially result in a hang, waiting for GLF_LOCK to clear. It doesn't happen very often, since it requires a glock that has not been used for a long time to be brought back into use at the same moment that the shrinker is part way through disposing of glocks. The fix is to set GLF_LOCK at a later time, when we already know that the other locks can be obtained. Also, we now only release the lru_lock in case a resched is needed, rather than on every iteration. Signed-off-by:

Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glock.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -1406,12 +1406,16 @@ __acquires(&lru_lock)
		gl = list_entry(list->next, struct gfs2_glock, gl_lru);
		list_del_init(&gl->gl_lru);
		if (!spin_trylock(&gl->gl_spin)) {
		add_back_to_lru:
		list_add(&gl->gl_lru, &lru_list);
		atomic_inc(&lru_count);
		continue;
		}
		if (test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
		spin_unlock(&gl->gl_spin);
		goto add_back_to_lru;
		}
		clear_bit(GLF_LRU, &gl->gl_flags);
		spin_unlock(&lru_lock);
		gl->gl_lockref.count++;
		if (demote_ok(gl))
		handle_callback(gl, LM_ST_UNLOCKED, 0, false);
		@@ -1419,7 +1423,7 @@ __acquires(&lru_lock)
		if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
		gl->gl_lockref.count--;
		spin_unlock(&gl->gl_spin);
		spin_lock(&lru_lock);
		cond_resched_lock(&lru_lock);
		}
		}

		@@ -1444,7 +1448,7 @@ static long gfs2_scan_glock_lru(int nr)
		gl = list_entry(lru_list.next, struct gfs2_glock, gl_lru);

		/* Test for being demotable */
		if (!test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
		if (!test_bit(GLF_LOCK, &gl->gl_flags)) {
		list_move(&gl->gl_lru, &dispose);
		atomic_dec(&lru_count);
		freed++;

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