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Commit 137d1a26c842a384c98dd2a6a605014fddf5c777

Authored by Anton Vorontsov
Committed by Linus Torvalds
1 parent 9bd0a07712
Exists in smarc-l5.0.0_1.0.0-ga and in 5 other branches 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

um: fix possible race on task->mm 

Checking for task->mm is dangerous as ->mm might disappear (exit_mm()
assigns NULL under task_lock(), so tasklist lock is not enough).

We can't use get_task_mm()/mmput() pair as mmput() might sleep, so let's
take the task lock while we care about its mm.

Note that we should also use find_lock_task_mm() to check all process'
threads for a valid mm, but for uml we'll do it in a separate patch.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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

arch/um/kernel/reboot.c
Diff comments   View file @ 137d1a2
... ... @@ -25,10 +25,13 @@
25 25  
26 26 read_lock(&tasklist_lock);
27 27 for_each_process(p) {
28   - if (p->mm == NULL)
  28 + task_lock(p);
  29 + if (!p->mm) {
  30 + task_unlock(p);
29 31 continue;
30   -
  32 + }
31 33 pid = p->mm->context.id.u.pid;
  34 + task_unlock(p);
32 35 os_kill_ptraced_process(pid, 1);
33 36 }
34 37 read_unlock(&tasklist_lock);