Re: [PATCH v1 4/6] LoongArch: Only send SIGTRAP signal if necessary in do_watch()

[Tiezhu Yang]

On 2026/8/31 下午10:02, Huacai Chen wrote:
> Hi, Tiezhu,
>
> On Wed, Aug 26, 2026 at 7:03 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
> > In do_watch(), the kernel unconditionally forces a SIGTRAP signal at the
> > end of the handler via force_sig(SIGTRAP). This is essential for ptrace
> > operations, but it severely disrupts standard perf_event usage.

...

> > @@ -811,6 +811,7 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
> >   asmlinkage void noinstr do_watch(struct pt_regs *regs)
> >   {
> >          irqentry_state_t state = irqentry_enter(regs);
> > +       bool perf_sigtrap = false;
> This is not for perf only, so need_sigtrap is better.
>
> >   #ifndef CONFIG_HAVE_HW_BREAKPOINT
> >          pr_warn("Hardware watch point handler not implemented!\n");
> > @@ -851,11 +852,12 @@ asmlinkage void noinstr do_watch(struct pt_regs *regs)
> >                          }
> >                  }
> >          } else {
> > -               breakpoint_handler(regs);
> > -               watchpoint_handler(regs);
> > +               perf_sigtrap |= breakpoint_handler(regs);
> > +               perf_sigtrap |= watchpoint_handler(regs);
> Let breakpoint_handler() and watchpoint_handler() return "int", then
> see below...
>
> >          }
> >
> > -       force_sig(SIGTRAP);
> > +       if (current->ptrace || perf_sigtrap)
> Define need_sigtrap as "int" and initialize it as current->ptrace,
> then we can only use "if (need_sigtrap)" here.

Thanks for your suggestion, it looks better.

But I think the type can be bool since it is either true or false.

Here is the incremental diff based on this v1 patch:

```
diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
index de0c9b03d551..4cbf84b148cd 100644
--- a/arch/loongarch/kernel/traps.c
+++ b/arch/loongarch/kernel/traps.c
@@ -811,7 +811,7 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
 asmlinkage void noinstr do_watch(struct pt_regs *regs)
 {
        irqentry_state_t state = irqentry_enter(regs);
-       bool perf_sigtrap = false;
+       bool need_sigtrap = !!current->ptrace;

 #ifndef CONFIG_HAVE_HW_BREAKPOINT
        pr_warn("Hardware watch point handler not implemented!\n");
@@ -852,11 +852,11 @@ asmlinkage void noinstr do_watch(struct pt_regs *regs)
                        }
                }
        } else {
-               perf_sigtrap |= breakpoint_handler(regs);
-               perf_sigtrap |= watchpoint_handler(regs);
+               need_sigtrap |= breakpoint_handler(regs);
+               need_sigtrap |= watchpoint_handler(regs);
        }

-       if (current->ptrace || perf_sigtrap)
+       if (need_sigtrap)
                force_sig(SIGTRAP);
 out:
 #endif
```

If you are OK with the above changes, I will send out v2 later.

Thanks,
Tiezhu