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Fix possible deadlock in 'lock-mutex'.

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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 <ludo@gnu.org>
This commit is contained in:
Olivier Dion 2022-11-05 12:59:23 -04:00 • committed by Ludovic Courtès
parent e47a153317
commit a1a85581f1
1 changed files with 10 additions and 9 deletions
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19
libguile/threads.c
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@ -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