Commit a64314e6 authored by Jan Lübbe's avatar Jan Lübbe Committed by Linus Torvalds

fix console change race exposed by CFS

The new behaviour of CFS exposes a race which occurs if a switch is
requested when vt_mode.mode is VT_PROCESS.

The process with vc->vt_pid is signaled before vc->vt_newvt is set.
This causes the switch to fail when triggered by the monitoing process
because the target is still -1.

[ If the signal sending fails, the subsequent "reset_vc(vc)" will then
  reset vt_newvt to -1, so this works for that case too.   - Linus ]
Signed-off-by: default avatarJan Lübbe <jluebbe@lasnet.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ed7fdff5
......@@ -1208,15 +1208,18 @@ void change_console(struct vc_data *new_vc)
/*
* Send the signal as privileged - kill_pid() will
* tell us if the process has gone or something else
* is awry
* is awry.
*
* We need to set vt_newvt *before* sending the signal or we
* have a race.
*/
vc->vt_newvt = new_vc->vc_num;
if (kill_pid(vc->vt_pid, vc->vt_mode.relsig, 1) == 0) {
/*
* It worked. Mark the vt to switch to and
* return. The process needs to send us a
* VT_RELDISP ioctl to complete the switch.
*/
vc->vt_newvt = new_vc->vc_num;
return;
}
......
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