From 2bae4205abd1583a5f3e2dfdc3174c1ef0c3828d Mon Sep 17 00:00:00 2001 From: Roman Arutyunyan Date: Wed, 4 Feb 2015 16:22:43 +0300 Subject: Core: fixed a race resulting in extra sem_post()'s. The mtx->wait counter was not decremented if we were able to obtain the lock right after incrementing it. This resulted in unneeded sem_post() calls, eventually leading to EOVERFLOW errors being logged, "sem_post() failed while wake shmtx (75: Value too large for defined data type)". To close the race, mtx->wait is now decremented if we obtain the lock right after incrementing it in ngx_shmtx_lock(). The result can become -1 if a concurrent ngx_shmtx_unlock() decrements mtx->wait before the added code does. However, that only leads to one extra iteration in the next call of ngx_shmtx_lock(). --- src/core/ngx_shmtx.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'src') diff --git a/src/core/ngx_shmtx.c b/src/core/ngx_shmtx.c index a62999f33..6230dc060 100644 --- a/src/core/ngx_shmtx.c +++ b/src/core/ngx_shmtx.c @@ -101,6 +101,7 @@ ngx_shmtx_lock(ngx_shmtx_t *mtx) (void) ngx_atomic_fetch_add(mtx->wait, 1); if (*mtx->lock == 0 && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid)) { + (void) ngx_atomic_fetch_add(mtx->wait, -1); return; } @@ -174,7 +175,7 @@ ngx_shmtx_wakeup(ngx_shmtx_t *mtx) wait = *mtx->wait; - if (wait == 0) { + if ((ngx_atomic_int_t) wait <= 0) { return; } -- cgit