From 8f17fc20bfb75bcec4cfeda789738979c8338fdc Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 15 Jun 2006 20:11:15 +0400 Subject: [PATCH] [PATCH] check_process_timers: fix possible lockup If the local timer interrupt happens just after do_exit() sets PF_EXITING (and before it clears ->it_xxx_expires) run_posix_cpu_timers() will call check_process_timers() with tasklist_lock + ->siglock held and check_process_timers: t = tsk; do { .... do { t = next_thread(t); } while (unlikely(t->flags & PF_EXITING)); } while (t != tsk); the outer loop will never stop. Actually, the window is bigger. Another process can attach the timer after ->it_xxx_expires was cleared (see the next commit) and the 'if (PF_EXITING)' check in arm_timer() is racy (see the one after that). Signed-off-by: Oleg Nesterov Signed-off-by: Linus Torvalds --- kernel/posix-cpu-timers.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 520f6c59948..9d9169aa2e2 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -1173,6 +1173,9 @@ static void check_process_timers(struct task_struct *tsk, } t = tsk; do { + if (unlikely(t->flags & PF_EXITING)) + continue; + ticks = cputime_add(cputime_add(t->utime, t->stime), prof_left); if (!cputime_eq(prof_expires, cputime_zero) && @@ -1193,11 +1196,7 @@ static void check_process_timers(struct task_struct *tsk, t->it_sched_expires > sched)) { t->it_sched_expires = sched; } - - do { - t = next_thread(t); - } while (unlikely(t->flags & PF_EXITING)); - } while (t != tsk); + } while ((t = next_thread(t)) != tsk); } } -- 2.20.1