Re: [PATCH] uprobes: Improve scalability by reducing the contention on siglock

[Oleg Nesterov]

On 08/08, Liao, Chang wrote:
>
>   - pre_ssout() resets the deny signal flag
>
>   - uprobe_deny_signal() sets the deny signal flag when TIF_SIGPENDING is 
> cleared.
>
>   - handle_singlestep() check the deny signal flag and restore TIF_SIGPENDING 
> if necessary.
>
> Does this approach look correct to you,do do you have any other way to 
> implement the "flag"?

Yes. But I don't think pre_ssout() needs to clear this flag. 
handle_singlestep() resets/clears
state, active_uprobe, frees insn slot. So I guess we only need


--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -2308,9 +2308,10 @@ static void handle_singlestep(struct upr
        utask->state = UTASK_RUNNING;
        xol_free_insn_slot(current);
 
-       spin_lock_irq(&current->sighand->siglock);
-       recalc_sigpending(); /* see uprobe_deny_signal() */
-       spin_unlock_irq(&current->sighand->siglock);
+       if (utask->xxx) {
+               set_thread_flag(TIF_SIGPENDING);
+               utask->xxx = 0;
+       }
 
        if (unlikely(err)) {
                uprobe_warn(current, "execute the probed insn, sending 
SIGILL.");

and that is all.

Oleg.