[PATCH] Allow system call restarts upon signal interruption

[Daniel Drake]

The X server frequently deals with SIGIO and SIGALRM interruptions.
If process execution is inside certain blocking system calls
when these signals arrive, e.g. with the kernel blocked on
a contended semaphore, the system calls will be interrupted.

Some system calls are automatically restartable (the kernel re-executes
them with the same parameters once the signal handler returns) but
only if the signal handler allows it.

Set SA_RESTART on the signal handlers to enable this convenient
behaviour.
---
 hw/xfree86/os-support/shared/sigio.c | 2 +-
 os/utils.c                           | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/xfree86/os-support/shared/sigio.c b/hw/xfree86/os-support/shared/sigio.c
index 45949f7..c746d02 100644
--- a/hw/xfree86/os-support/shared/sigio.c
+++ b/hw/xfree86/os-support/shared/sigio.c
@@ -178,7 +178,7 @@ xf86InstallSIGIOHandler(int fd, void (*f) (int, void *), void *closure)
             }
             sigemptyset(&sa.sa_mask);
             sigaddset(&sa.sa_mask, SIGIO);
-            sa.sa_flags = 0;
+            sa.sa_flags = SA_RESTART;
             sa.sa_handler = xf86SIGIO;
             sigaction(SIGIO, &sa, &osa);
             xf86SigIOFuncs[i].fd = fd;
diff --git a/os/utils.c b/os/utils.c
index 75769f1..e2e59a8 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -1220,6 +1220,7 @@ SmartScheduleInit(void)
     memset((char *) &act, 0, sizeof(struct sigaction));
 
     /* Set up the timer signal function */
+    act.sa_flags = SA_RESTART;
     act.sa_handler = SmartScheduleTimer;
     sigemptyset(&act.sa_mask);
     sigaddset(&act.sa_mask, SIGALRM);
-- 
2.1.4