From: Anton Vorontsov Date: Thu, 31 May 2012 23:26:25 +0000 (-0700) Subject: um: fix possible race on task->mm X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=137d1a26c842a384c98dd2a6a605014fddf5c777;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git 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 Cc: Richard Weinberger Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c index 66d754c46e7b..1411f4e79f9a 100644 --- a/arch/um/kernel/reboot.c +++ b/arch/um/kernel/reboot.c @@ -25,10 +25,13 @@ static void kill_off_processes(void) read_lock(&tasklist_lock); for_each_process(p) { - if (p->mm == NULL) + task_lock(p); + if (!p->mm) { + task_unlock(p); continue; - + } pid = p->mm->context.id.u.pid; + task_unlock(p); os_kill_ptraced_process(pid, 1); } read_unlock(&tasklist_lock);