Messages in this thread Patch in this message | | | Date | Thu, 7 May 2009 08:46:50 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 5/5] do_wait: fix the theoretical race with stop/trace/cont |
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do_wait:
current->state = TASK_INTERRUPTIBLE;
read_lock(&tasklist_lock); ... search for the task to reap ...
In theory, the ->state changing can leak into the critical section. Since the child can change its status under read_lock(tasklist) in parallel (finish_stop/ptrace_stop), we can miss the wakeup if __wake_up_parent() sees us in TASK_RUNNING state. Add the barrier.
Also, use __set_current_state() to set TASK_RUNNING.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> ---
kernel/exit.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- PTRACE/kernel/exit.c~5_MB 2009-05-07 05:34:40.000000000 +0200 +++ PTRACE/kernel/exit.c 2009-05-07 05:43:06.000000000 +0200 @@ -1581,7 +1581,7 @@ repeat: (!wo->wo_pid || hlist_empty(&wo->wo_pid->tasks[wo->wo_type]))) goto notask; - current->state = TASK_INTERRUPTIBLE; + set_current_state(TASK_INTERRUPTIBLE); read_lock(&tasklist_lock); tsk = current; do { @@ -1608,7 +1608,7 @@ notask: } } end: - current->state = TASK_RUNNING; + __set_current_state(TASK_RUNNING); remove_wait_queue(¤t->signal->wait_chldexit,&wait); if (wo->wo_info) { struct siginfo __user *infop = wo->wo_info;
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