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Date:   Tue, 23 Mar 2021 22:41:40 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Like Xu <like.xu@linux.intel.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        Kan Liang <kan.liang@linux.intel.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 RESEND 3/5] perf/x86/lbr: Move cpuc->lbr_xsave
 allocation out of sleeping region
Message-ID: <20210323214140.GE4746@worktop.programming.kicks-ass.net>
References: <20210322060635.821531-1-like.xu@linux.intel.com>
 <20210322060635.821531-4-like.xu@linux.intel.com>
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On Mon, Mar 22, 2021 at 02:06:33PM +0800, Like Xu wrote:
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 18df17129695..a4ce669cc78d 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -373,7 +373,7 @@ set_ext_hw_attr(struct hw_perf_event *hwc, struct perf_event *event)
>  	return x86_pmu_extra_regs(val, event);
>  }
>  
> -int x86_reserve_hardware(void)
> +int x86_reserve_hardware(struct perf_event *event)
>  {
>  	int err = 0;
>  
> @@ -382,8 +382,10 @@ int x86_reserve_hardware(void)
>  		if (atomic_read(&pmc_refcount) == 0) {
>  			if (!reserve_pmc_hardware())
>  				err = -EBUSY;
> -			else
> +			else {
>  				reserve_ds_buffers();
> +				reserve_lbr_buffers(event);
> +			}
>  		}
>  		if (!err)
>  			atomic_inc(&pmc_refcount);

This makes absolutely no sense what so ever. This is only executed for
the first event that gets here.