From a64314e62d89562b6fc77593648bec3acc35bf61 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20L=C3=BCbbe?= <jluebbe@lasnet.de>
Date: Sat, 29 Sep 2007 18:47:51 +0200
Subject: [PATCH] fix console change race exposed by CFS
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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: Jan Lübbe <jluebbe@lasnet.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
drivers/char/vt_ioctl.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index c6f6f42097391..045e6888d15ba 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -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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