linux-kernel - Re: [PATCH v3 26/57] perf: Simplify event

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Date:   Mon, 12 Jun 2023 22:56:06 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, keescook@...omium.org,
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Subject: Re: [PATCH v3 26/57] perf: Simplify event_function*()

Hi Peter,

On Mon, Jun 12, 2023 at 2:39 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Use guards to reduce gotos and simplify control flow.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/events/core.c |   39 ++++++++++++++++++++++++++-------------
>  1 file changed, 26 insertions(+), 13 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -214,6 +214,25 @@ struct event_function_struct {
>         void *data;
>  };
>
> +typedef struct {
> +       struct perf_cpu_context *cpuctx;
> +       struct perf_event_context *ctx;
> +} class_perf_ctx_lock_t;
> +
> +static inline void class_perf_ctx_lock_destructor(class_perf_ctx_lock_t *_T)
> +{
> +       if (_T->cpuctx)
> +               perf_ctx_unlock(_T->cpuctx, _T->ctx);

Shouldn't it be called unconditionally?

Thanks,
Namhyung

> +}
> +
> +static inline class_perf_ctx_lock_t
> +class_perf_ctx_lock_constructor(struct perf_cpu_context *cpuctx,
> +                               struct perf_event_context *ctx)
> +{
> +       perf_ctx_lock(cpuctx, ctx);
> +       return (class_perf_ctx_lock_t){ cpuctx, ctx };
> +}
> +
>  static int event_function(void *info)
>  {
>         struct event_function_struct *efs = info;
> @@ -224,17 +243,15 @@ static int event_function(void *info)
>         int ret = 0;
>
>         lockdep_assert_irqs_disabled();
> +       guard(perf_ctx_lock)(cpuctx, task_ctx);
>
> -       perf_ctx_lock(cpuctx, task_ctx);
>         /*
>          * Since we do the IPI call without holding ctx->lock things can have
>          * changed, double check we hit the task we set out to hit.
>          */
>         if (ctx->task) {
> -               if (ctx->task != current) {
> -                       ret = -ESRCH;
> -                       goto unlock;
> -               }
> +               if (ctx->task != current)
> +                       return -ESRCH;
>
>                 /*
>                  * We only use event_function_call() on established contexts,
> @@ -254,8 +271,6 @@ static int event_function(void *info)
>         }
>
>         efs->func(event, cpuctx, ctx, efs->data);
> -unlock:
> -       perf_ctx_unlock(cpuctx, task_ctx);
>
>         return ret;
>  }
> @@ -329,11 +344,11 @@ static void event_function_local(struct
>                 task_ctx = ctx;
>         }
>
> -       perf_ctx_lock(cpuctx, task_ctx);
> +       guard(perf_ctx_lock)(cpuctx, task_ctx);
>
>         task = ctx->task;
>         if (task == TASK_TOMBSTONE)
> -               goto unlock;
> +               return;
>
>         if (task) {
>                 /*
> @@ -343,18 +358,16 @@ static void event_function_local(struct
>                  */
>                 if (ctx->is_active) {
>                         if (WARN_ON_ONCE(task != current))
> -                               goto unlock;
> +                               return;
>
>                         if (WARN_ON_ONCE(cpuctx->task_ctx != ctx))
> -                               goto unlock;
> +                               return;
>                 }
>         } else {
>                 WARN_ON_ONCE(&cpuctx->ctx != ctx);
>         }
>
>         func(event, cpuctx, ctx, data);
> -unlock:
> -       perf_ctx_unlock(cpuctx, task_ctx);
>  }
>
>  #define PERF_FLAG_ALL (PERF_FLAG_FD_NO_GROUP |\
>
>