[PATCH] uml: fix SIGWINCH handler race while waiting for signals.

If a SIGWINCH comes in, while winch_thread() isn't waiting in wait(),
winch_thread could miss signals.  It isn't very probable, that anyone will
see this causing trouble, as it would need a very special timing, that a
missed SIGWINCH results in a wrong window size.

So, this is a minor problem.  But why not fix, as it can be done so easy?

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index 5d37681..de3bce7 100644 (file)
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -63,7 +63,7 @@ error:
  *
  * SIGWINCH can't be received synchronously, so you have to set up to receive it
  * as a signal.  That being the case, if you are going to wait for it, it is
- * convenient to sit in a pause() and wait for the signal to bounce you out of
+ * convenient to sit in sigsuspend() and wait for the signal to bounce you out of
  * it (see below for how we make sure to exit only on SIGWINCH).
  */
 
@@ -94,18 +94,19 @@ static int winch_thread(void *arg)
                       "byte, err = %d\n", -count);
 
        /* We are not using SIG_IGN on purpose, so don't fix it as I thought to
-        * do! If using SIG_IGN, the pause() call below would not stop on
+        * do! If using SIG_IGN, the sigsuspend() call below would not stop on
         * SIGWINCH. */
 
        signal(SIGWINCH, winch_handler);
        sigfillset(&sigs);
-       sigdelset(&sigs, SIGWINCH);
-       /* Block anything else than SIGWINCH. */
+       /* Block all signals possible. */
        if(sigprocmask(SIG_SETMASK, &sigs, NULL) < 0){
                printk("winch_thread : sigprocmask failed, errno = %d\n", 
                       errno);
                exit(1);
        }
+       /* In sigsuspend(), block anything else than SIGWINCH. */
+       sigdelset(&sigs, SIGWINCH);
 
        if(setsid() < 0){
                printk("winch_thread : setsid failed, errno = %d\n", errno);
@@ -130,7 +131,7 @@ static int winch_thread(void *arg)
        while(1){
                /* This will be interrupted by SIGWINCH only, since other signals
                 * are blocked.*/
-               pause();
+               sigsuspend(&sigs);
 
                count = os_write_file(pipe_fd, &c, sizeof(c));
                if(count != sizeof(c))