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authorMichal Januszewski <spock@gentoo.org>2007-04-19 16:34:50 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2007-05-01 17:06:00 -0700
commit93c27c733bcab7cc19cc77dc5fb8b605921adf59 (patch)
treeb20b20d93b103dacd0aee45596b4915c49d4818d
parent21deacabe2e2b0b823dc9593f88af3fec103a974 (diff)
vt: fix potential race in VT_WAITACTIVE handler
[PATCH] vt: fix potential race in 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> Acked-by: Antonino Daplas <adaplas@pol.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Chuck Ebbert <cebbert@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--drivers/char/vt_ioctl.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index dc8368ebb1ac..60740a19cb54 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -1038,10 +1038,22 @@ int vt_waitactive(int vt)
add_wait_queue(&vt_activate_queue, &wait);
for (;;) {
- set_current_state(TASK_INTERRUPTIBLE);
retval = 0;
- if (vt == fg_console)
+
+ /*
+ * Synchronize with redraw_screen(). By acquiring the console
+ * semaphore we make sure that the console switch is completed
+ * before we return. If we didn't wait for the semaphore, we
+ * could return at a point where fg_console has already been
+ * updated, but the console switch hasn't been completed.
+ */
+ acquire_console_sem();
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (vt == fg_console) {
+ release_console_sem();
break;
+ }
+ release_console_sem();
retval = -EINTR;
if (signal_pending(current))
break;