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>
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@ -25,10 +25,13 @@ static void kill_off_processes(void)
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read_lock(&tasklist_lock);
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for_each_process(p) {
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if (p->mm == NULL)
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task_lock(p);
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if (!p->mm) {
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task_unlock(p);
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continue;
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}
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pid = p->mm->context.id.u.pid;
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task_unlock(p);
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os_kill_ptraced_process(pid, 1);
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}
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read_unlock(&tasklist_lock);
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