linux-kernel - Re: [tip: perf/core] perf/x86: Reset the dirty counter to prevent the leak for an RDPMC task

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Date:   Fri, 16 Apr 2021 18:45:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>, x86@...nel.org
Subject: Re: [tip: perf/core] perf/x86: Reset the dirty counter to prevent
 the leak for an RDPMC task

On Fri, Apr 16, 2021 at 03:01:48PM -0000, tip-bot2 for Kan Liang wrote:
> @@ -2331,6 +2367,9 @@ static void x86_pmu_event_unmapped(struct perf_event *event, struct mm_struct *m
>  	if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED))
>  		return;
>  
> +	if (x86_pmu.sched_task && event->hw.target)
> +		perf_sched_cb_dec(event->ctx->pmu);
> +
>  	if (atomic_dec_and_test(&mm->context.perf_rdpmc_allowed))
>  		on_each_cpu_mask(mm_cpumask(mm), cr4_update_pce, NULL, 1);
>  }

'perf test' on a kernel with CONFIG_DEBUG_PREEMPT=y gives:

[  244.439538] BUG: using smp_processor_id() in preemptible [00000000] code: perf/1771
[  244.448144] caller is perf_sched_cb_dec+0xa/0x70
[  244.453314] CPU: 28 PID: 1771 Comm: perf Not tainted 5.12.0-rc3-00026-gb04c0cddff6d #595
[  244.462347] Hardware name: Intel Corporation S2600GZ/S2600GZ, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013
[  244.473804] Call Trace:
[  244.476535]  dump_stack+0x6d/0x89
[  244.480237]  check_preemption_disabled+0xc8/0xd0
[  244.485394]  perf_sched_cb_dec+0xa/0x70
[  244.489677]  x86_pmu_event_unmapped+0x35/0x60
[  244.494541]  perf_mmap_close+0x76/0x580
[  244.498833]  remove_vma+0x31/0x70
[  244.502535]  __do_munmap+0x2e8/0x4e0
[  244.506531]  __vm_munmap+0x7e/0x120
[  244.510429]  __x64_sys_munmap+0x28/0x30
[  244.514712]  do_syscall_64+0x33/0x80
[  244.518701]  entry_SYSCALL_64_after_hwframe+0x44/0xae


Obviously I tested that after I pushed it out :/