Messages in this thread Patch in this message | | | From | Jan Luebbe <> | Date | Sat, 29 Sep 2007 18:47:51 +0200 | Subject | [PATCH] fix console change race exposed by CFS |
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From: Jan Lübbe <jluebbe@lasnet.de>
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.
Signed-off-by: Jan Lübbe <jluebbe@lasnet.de> --- Index: linux-2.6.22/drivers/char/vt_ioctl.c =================================================================== --- linux-2.6.22.orig/drivers/char/vt_ioctl.c +++ linux-2.6.22/drivers/char/vt_ioctl.c @@ -1208,15 +1208,18 @@ /* * 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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