xwayland-shm: block signals during fallocate

posix_fallocate() does an explicit rollback if it gets EINTR, and
this is a problem on slow systems because when the allocation size
is sufficiently large posix_fallocate() will always be interrupted
by the smart scheduler's SIGALRM.

Changes since v1 - big comment in the code to explain what is going on

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Ian Ray <ian.ray@ge.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Daniel Stone <daniels@collabora.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/hw/xwayland/xwayland-shm.c b/hw/xwayland/xwayland-shm.c
index daf61480d..452d1f509 100644
--- a/hw/xwayland/xwayland-shm.c
+++ b/hw/xwayland/xwayland-shm.c
@@ -28,6 +28,8 @@
 #include <dix-config.h>
 #endif
 
+#include "os.h"
+
 #include "xwayland.h"
 
 #include <sys/mman.h>
@@ -139,9 +141,17 @@ os_create_anonymous_file(off_t size)
         return -1;
 
 #ifdef HAVE_POSIX_FALLOCATE
+    /*
+     * posix_fallocate does an explicit rollback if it gets EINTR.
+     * Temporarily block signals to allow the call to succeed on
+     * slow systems where the smart scheduler's SIGALRM prevents
+     * large allocation attempts from ever succeeding.
+     */
+    OsBlockSignals();
     do {
         ret = posix_fallocate(fd, 0, size);
     } while (ret == EINTR);
+    OsReleaseSignals();
 
     if (ret != 0) {
         close(fd);