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Commit a64314e62d89562b6fc77593648bec3acc35bf61

Authored by Jan Lübbe
Committed by Linus Torvalds
1 parent ed7fdff5d6
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

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>

Showing 1 changed file with 5 additions and 2 deletions Side-by-side Diff

drivers/char/vt_ioctl.c
Diff comments   View file @ a64314e
... ... @@ -1208,15 +1208,18 @@
1208 1208 /*
1209 1209 * Send the signal as privileged - kill_pid() will
1210 1210 * tell us if the process has gone or something else
1211   - * is awry
  1211 + * is awry.
  1212 + *
  1213 + * We need to set vt_newvt *before* sending the signal or we
  1214 + * have a race.
1212 1215 */
  1216 + vc->vt_newvt = new_vc->vc_num;
1213 1217 if (kill_pid(vc->vt_pid, vc->vt_mode.relsig, 1) == 0) {
1214 1218 /*
1215 1219 * It worked. Mark the vt to switch to and
1216 1220 * return. The process needs to send us a
1217 1221 * VT_RELDISP ioctl to complete the switch.
1218 1222 */
1219   - vc->vt_newvt = new_vc->vc_num;
1220 1223 return;
1221 1224 }
1222 1225