-stable review patch. If anyone has any objections, please let us know. ------------------ From: Michal Januszewski [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 Acked-by: Antonino Daplas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Cc: Chuck Ebbert Signed-off-by: Greg Kroah-Hartman --- drivers/char/vt_ioctl.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) --- 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; -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/