[vlc-devel] [PATCH] Avoid deadlock on UDP stop

[Romain Vimont]

The call to block_FifoWake() at the end of udp.c/ThreadRead() is not
sufficient to always prevent block_FifoGet() in udp.c/BlockUDP() from
blocking indefinitely: it will at most wake up the first, but following
calls (if any) will never be awakened, causing a deadlock.

A new flag keeping the "finishing" state of the UDP access is sufficient
to prevent the deadlock, avoiding unwanted calls to block_FifoGet().

Signed-off-by: Romain Vimont <rom at rom1v.com>
---
 modules/access/udp.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/modules/access/udp.c b/modules/access/udp.c
index 3c18cb8..0e4fc4d 100644
--- a/modules/access/udp.c
+++ b/modules/access/udp.c
@@ -42,6 +42,7 @@
 #include <vlc_access.h>
 #include <vlc_network.h>
 #include <vlc_block.h>
+#include <vlc_atomic.h>
 
 #define MTU 65535
 
@@ -75,6 +76,7 @@ struct access_sys_t
     size_t fifo_size;
     block_fifo_t *fifo;
     vlc_thread_t thread;
+    atomic_bool b_finishing;
 };
 
 /*****************************************************************************
@@ -166,6 +168,8 @@ static int Open( vlc_object_t *p_this )
 
     sys->fifo_size = var_InheritInteger( p_access, "udp-buffer");
 
+    sys->b_finishing = false;
+
     if( vlc_clone( &sys->thread, ThreadRead, p_access,
                    VLC_THREAD_PRIORITY_INPUT ) )
     {
@@ -231,6 +235,13 @@ static block_t *BlockUDP( access_t *p_access )
 {
     access_sys_t *sys = p_access->p_sys;
 
+    if( unlikely( atomic_load( &sys->b_finishing ) ) )
+    {
+        /* We should not read data anymore */
+        p_access->info.b_eof = true;
+        return NULL;
+    }
+
     return block_FifoGet( sys->fifo );
 }
 
@@ -270,6 +281,7 @@ static void* ThreadRead( void *data )
         block_FifoPut( sys->fifo, pkt );
     }
 
+    atomic_store( &sys->b_finishing, true );
     block_FifoWake( sys->fifo );
     return NULL;
 }
-- 
1.7.10.4