Mercurial > hg > nginx-quic
changeset 6080:4296627f385a stable-1.6
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().
author | Roman Arutyunyan <arut@nginx.com> |
---|---|
date | Wed, 04 Feb 2015 16:22:43 +0300 |
parents | 8e56f649fd0d |
children | 12ab5cd445c0 |
files | src/core/ngx_shmtx.c |
diffstat | 1 files changed, 2 insertions(+), 1 deletions(-) [+] |
line wrap: on
line diff
--- 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; }