From d76d1815f3e72fb627ad7f95ef63120b0a557c9c Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Sun, 2 Jan 2011 21:28:34 -0500 Subject: [PATCH] svcrpc: avoid double reply caused by deferral race Commit d29068c431599fa "sunrpc: Simplify cache_defer_req and related functions." asserted that cache_check() could determine success or failure of cache_defer_req() by checking the CACHE_PENDING bit. This isn't quite right. We need to know whether cache_defer_req() created a deferred request, in which case sending an rpc reply has become the responsibility of the deferred request, and it is important that we not send our own reply, resulting in two different replies to the same request. And the CACHE_PENDING bit doesn't tell us that; we could have succesfully created a deferred request at the same time as another thread cleared the CACHE_PENDING bit. So, partially revert that commit, to ensure that cache_check() returns -EAGAIN if and only if a deferred request has been created. Signed-off-by: J. Bruce Fields Acked-by: NeilBrown --- net/sunrpc/cache.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c index e433e7580e27..0d6002f26d82 100644 --- a/net/sunrpc/cache.c +++ b/net/sunrpc/cache.c @@ -37,7 +37,7 @@ #define RPCDBG_FACILITY RPCDBG_CACHE -static void cache_defer_req(struct cache_req *req, struct cache_head *item); +static bool cache_defer_req(struct cache_req *req, struct cache_head *item); static void cache_revisit_request(struct cache_head *item); static void cache_init(struct cache_head *h) @@ -268,9 +268,11 @@ int cache_check(struct cache_detail *detail, } if (rv == -EAGAIN) { - cache_defer_req(rqstp, h); - if (!test_bit(CACHE_PENDING, &h->flags)) { - /* Request is not deferred */ + if (!cache_defer_req(rqstp, h)) { + /* + * Request was not deferred; handle it as best + * we can ourselves: + */ rv = cache_is_valid(detail, h); if (rv == -EAGAIN) rv = -ETIMEDOUT; @@ -618,18 +620,19 @@ static void cache_limit_defers(void) discard->revisit(discard, 1); } -static void cache_defer_req(struct cache_req *req, struct cache_head *item) +/* Return true if and only if a deferred request is queued. */ +static bool cache_defer_req(struct cache_req *req, struct cache_head *item) { struct cache_deferred_req *dreq; if (req->thread_wait) { cache_wait_req(req, item); if (!test_bit(CACHE_PENDING, &item->flags)) - return; + return false; } dreq = req->defer(req); if (dreq == NULL) - return; + return false; setup_deferral(dreq, item, 1); if (!test_bit(CACHE_PENDING, &item->flags)) /* Bit could have been cleared before we managed to @@ -638,6 +641,7 @@ static void cache_defer_req(struct cache_req *req, struct cache_head *item) cache_revisit_request(item); cache_limit_defers(); + return true; } static void cache_revisit_request(struct cache_head *item)