From a1a85581f17dade76a598b48eac7d3d308e3a0a5 Mon Sep 17 00:00:00 2001 From: Olivier Dion Date: Sat, 5 Nov 2022 12:59:23 -0400 Subject: Fix possible deadlock in 'lock-mutex'. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit If we got interrupted while waiting on our condition variable, we unlock the kernel mutex momentarily while executing asynchronous operations before putting us back into the waiting queue. However, we have to retry acquiring the mutex before getting back into the queue, otherwise it's possible that we wait indefinitely since nobody could be the owner for a while. * libguile/threads.c (lock_mutex): Try acquring the mutex after signal interruption. Signed-off-by: Ludovic Courtès --- libguile/threads.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) (limited to 'libguile') diff --git a/libguile/threads.c b/libguile/threads.c index 280d306bf..0f5cf2ed5 100644 --- a/libguile/threads.c +++ b/libguile/threads.c @@ -1022,14 +1022,7 @@ lock_mutex (enum scm_mutex_kind kind, struct scm_mutex *m, if (err == 0) { - if (scm_is_eq (m->owner, SCM_BOOL_F)) - { - m->owner = current_thread->handle; - scm_i_pthread_mutex_unlock (&m->lock); - return SCM_BOOL_T; - } - else - continue; + goto maybe_acquire; } else if (err == ETIMEDOUT) { @@ -1041,7 +1034,7 @@ lock_mutex (enum scm_mutex_kind kind, struct scm_mutex *m, scm_i_pthread_mutex_unlock (&m->lock); scm_async_tick (); scm_i_scm_pthread_mutex_lock (&m->lock); - continue; + goto maybe_acquire; } else { @@ -1050,6 +1043,14 @@ lock_mutex (enum scm_mutex_kind kind, struct scm_mutex *m, errno = err; SCM_SYSERROR; } + + maybe_acquire: + if (scm_is_eq (m->owner, SCM_BOOL_F)) + { + m->owner = current_thread->handle; + scm_i_pthread_mutex_unlock (&m->lock); + return SCM_BOOL_T; + } } } #undef FUNC_NAME -- cgit v1.2.1