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[PATCH] vt: fix potential race in VT_WAITACTIVE handler

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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 <[email protected]>
Acked-by: Antonino Daplas <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Michal Januszewski 2007-04-01 23:49:51 -07:00 • committed by Linus Torvalds
commit f991519c19
1 changed files with 14 additions and 2 deletions
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16
drivers/char/vt_ioctl.c
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@ -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;