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Commit f991519c authored by Michal Januszewski's avatar Michal Januszewski Committed by Linus Torvalds
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[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: default avatarMichal Januszewski <spock@gentoo.org>
Acked-by: default avatarAntonino Daplas <adaplas@pol.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1d64b9cb

drivers/char/vt_ioctl.c

+14 −2
Original line number Diff line number Diff line
@@ -1039,10 +1039,22 @@ 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;