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Subject[PATCH] vt: fix a potential race in the VT_WAITACTIVE handler
On a multiprocessor machine the VT_WAITACTIVE ioctl call may return 0
if fg_console has already been updated in redraw_screen(), but the
console switch itself hasn't been completed. Fix this by checking
fg_console in vt_waitactive() with the console sem held.

Signed-off-by: Michal Januszewski <spock@gentoo.org>

---
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index 3a5d301..00b5b34 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -1041,8 +1041,12 @@ int vt_waitactive(int vt)
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
retval = 0;
- if (vt == fg_console)
+ acquire_console_sem();
+ if (vt == fg_console) {
+ release_console_sem();
break;
+ }
+ release_console_sem();
retval = -EINTR;
if (signal_pending(current))
break;
-
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