Return-Path: linux-nfs-owner@vger.kernel.org Received: from cantor2.suse.de ([195.135.220.15]:55245 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755915Ab3BZGiv (ORCPT ); Tue, 26 Feb 2013 01:38:51 -0500 From: NeilBrown To: "J. Bruce Fields" Date: Tue, 26 Feb 2013 17:36:42 +1100 Subject: [PATCH 1/2] sunrpc/cache: remove races with queuing an upcall. Cc: Bodo Stroesser , linux-nfs@vger.kernel.org Message-ID: <20130226063641.6063.80045.stgit@notabene.brown> In-Reply-To: <20130226063637.6063.34934.stgit@notabene.brown> References: <20130226063637.6063.34934.stgit@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: We currently queue an upcall after setting CACHE_PENDING, and dequeue after clearing CACHE_PENDING. So a request should only be present when CACHE_PENDING is set. However we don't combine the test and the enqueue/dequeue in a protected region, so it is possible (if unlikely) for a race to result in a request being queued without CACHE_PENDING set, or a request to be absent despite CACHE_PENDING. So: include a test for CACHE_PENDING inside the regions of enqueue and dequeue where queue_lock is held, and abort the operation if the value is not as expected. With this, it perfectly safe and correct to: - call cache_dequeue() if and only if we have just cleared CACHE_PENDING - call sunrpc_cache_pipe_upcall() (via cache_make_upcall) if and only if we have just set CACHE_PENDING. Reported-by: Bodo Stroesser Signed-off-by: NeilBrown --- net/sunrpc/cache.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c index 9afa439..b48c8ef 100644 --- a/net/sunrpc/cache.c +++ b/net/sunrpc/cache.c @@ -1022,6 +1022,9 @@ static void cache_dequeue(struct cache_detail *detail, struct cache_head *ch) struct cache_request *cr = container_of(cq, struct cache_request, q); if (cr->item != ch) continue; + if (test_bit(CACHE_PENDING, &ch->flags)) + /* Lost a race and it is pending again */ + break; if (cr->readers != 0) continue; list_del(&cr->q.list); @@ -1151,6 +1154,7 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h, struct cache_request *crq; char *bp; int len; + int ret = 0; if (!cache_listeners_exist(detail)) { warn_no_listener(detail); @@ -1182,10 +1186,18 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h, crq->len = PAGE_SIZE - len; crq->readers = 0; spin_lock(&queue_lock); - list_add_tail(&crq->q.list, &detail->queue); + if (test_bit(CACHE_PENDING, &h->flags)) + list_add_tail(&crq->q.list, &detail->queue); + else + /* Lost a race, no longer PENDING, so don't enqueue */ + ret = -EAGAIN; spin_unlock(&queue_lock); wake_up(&queue_wait); - return 0; + if (ret == -EAGAIN) { + kfree(buf); + kfree(crq); + } + return ret; } EXPORT_SYMBOL_GPL(sunrpc_cache_pipe_upcall);