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authorJan Lübbe <jluebbe@lasnet.de>2007-09-29 18:47:51 +0200
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-09-29 10:00:15 -0700
commita64314e62d89562b6fc77593648bec3acc35bf61 (patch)
tree964aba05c1293c2436088905001595a8209e44d1
parented7fdff5d6754f9ef9e47bbf0b171d3d96fb7e41 (diff)
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: Jan Lübbe <jluebbe@lasnet.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--drivers/char/vt_ioctl.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index c6f6f420973..045e6888d15 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;
}