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GFS2: Fix race in glock lru glock disposal

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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>
This commit is contained in:
Steven Whitehouse 2014-06-23 14:43:32 +01:00
parent 79272b3562
commit 94a09a3999
1 changed files with 7 additions and 3 deletions
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10
fs/gfs2/glock.c
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@ -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++;