On 3/4/21 5:23 AM, Stefan Metzmacher wrote:
>
> Hi Jens,
>
>> +static pid_t fork_thread(int (*fn)(void *), void *arg)
>> +{
>> + unsigned long flags = CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|
>> + CLONE_IO|SIGCHLD;
>> + struct kernel_clone_args args = {
>> + .flags = ((lower_32_bits(flags) | CLONE_VM |
>> + CLONE_UNTRACED) & ~CSIGNAL),
>> + .exit_signal = (lower_32_bits(flags) & CSIGNAL),
>> + .stack = (unsigned long)fn,
>> + .stack_size = (unsigned long)arg,
>> + };
>> +
>> + return kernel_clone(&args);
>> +}
>
> Can you please explain why CLONE_SIGHAND is used here?
We can't have CLONE_THREAD without CLONE_SIGHAND... The io-wq workers
don't really care about signals, we don't use them internally.
> Will the userspace signal handlers executed from the kernel thread?
No
> Will SIGCHLD be posted to the userspace signal handlers in a userspace
> process? Will wait() from userspace see the exit of a thread?
Currently actually it does, but I think that's just an oversight. As far
as I can tell, we want to add something like the below. Untested... I'll
give this a spin in a bit.
diff --git a/kernel/signal.c b/kernel/signal.c
index ba4d1ef39a9e..e5db1d8f18e5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1912,6 +1912,10 @@ bool do_notify_parent(struct task_struct *tsk, int sig)
bool autoreap = false;
u64 utime, stime;
+ /* Don't notify a parent task if an io_uring worker exits */
+ if (tsk->flags & PF_IO_WORKER)
+ return true;
+
BUG_ON(sig == -1);
/* do_notify_parent_cldstop should have been called instead. */
--
Jens Axboe
