From: Mathieu Desnoyers Date: Mon, 6 Jul 2015 21:28:34 +0000 (-0400) Subject: Fix: handle sys_futex() FUTEX_WAIT interrupted by signal X-Git-Tag: v2.7.0-rc1~10 X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=commitdiff_plain;h=549731b7fc86d6dfb63f1cbd03991f59567f96ba Fix: handle sys_futex() FUTEX_WAIT interrupted by signal We need to handle EINTR returned by sys_futex() FUTEX_WAIT, otherwise a signal interrupting this system call could make sys_futex return too early, and therefore cause a synchronization issue. Signed-off-by: Mathieu Desnoyers Signed-off-by: Jérémie Galarneau --- diff --git a/src/common/futex.c b/src/common/futex.c index 7f07b1118..078186743 100644 --- a/src/common/futex.c +++ b/src/common/futex.c @@ -55,8 +55,11 @@ void futex_wait_update(int32_t *futex, int active) { if (active) { uatomic_set(futex, 1); - futex_async(futex, FUTEX_WAKE, - INT_MAX, NULL, NULL, 0); + if (futex_async(futex, FUTEX_WAKE, + INT_MAX, NULL, NULL, 0) < 0) { + PERROR("futex_async"); + abort(); + } } else { uatomic_set(futex, 0); } @@ -84,10 +87,23 @@ void futex_nto1_wait(int32_t *futex) { cmm_smp_mb(); - if (uatomic_read(futex) == -1) { - futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0); + if (uatomic_read(futex) != -1) + goto end; + while (futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0)) { + switch (errno) { + case EWOULDBLOCK: + /* Value already changed. */ + goto end; + case EINTR: + /* Retry if interrupted by signal. */ + break; /* Get out of switch. */ + default: + /* Unexpected error. */ + PERROR("futex_async"); + abort(); + } } - +end: DBG("Futex n to 1 wait done"); } @@ -97,10 +113,13 @@ void futex_nto1_wait(int32_t *futex) LTTNG_HIDDEN void futex_nto1_wake(int32_t *futex) { - if (caa_unlikely(uatomic_read(futex) == -1)) { - uatomic_set(futex, 0); - futex_async(futex, FUTEX_WAKE, 1, NULL, NULL, 0); + if (caa_unlikely(uatomic_read(futex) != -1)) + goto end; + uatomic_set(futex, 0); + if (futex_async(futex, FUTEX_WAKE, 1, NULL, NULL, 0) < 0) { + PERROR("futex_async"); + abort(); } - +end: DBG("Futex n to 1 wake done"); }