From 94a09a3999ee978e097b5aad74034ed43bae56db Mon Sep 17 00:00:00 2001 From: Steven Whitehouse Date: Mon, 23 Jun 2014 14:43:32 +0100 Subject: GFS2: Fix race in glock lru glock disposal 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 --- fs/gfs2/glock.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'fs') diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c index 278fae5b6982..c1e5b126d2ca 100644 --- a/fs/gfs2/glock.c +++ b/fs/gfs2/glock.c @@ -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++; -- cgit v1.2.3