[Guile-commits] 02/02: Fix possible deadlock in 'lock-mutex'.

[Ludovic Courtès]

civodul pushed a commit to branch main
in repository guile.

commit a1a85581f17dade76a598b48eac7d3d308e3a0a5
Author: Olivier Dion <olivier.dion@polymtl.ca>
AuthorDate: Sat Nov 5 12:59:23 2022 -0400

    Fix possible deadlock in 'lock-mutex'.
    
    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>
---
 libguile/threads.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

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