linux-kernel - Re: [tip: perf/core] perf/core: Fix endless multiplex timer

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Date:   Thu, 6 Aug 2020 20:53:53 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>
Subject: Re: [tip: perf/core] perf/core: Fix endless multiplex timer

On Thu, Aug 06, 2020 at 07:11:24PM +0100, Robin Murphy wrote:
> On 2020-03-20 12:58, tip-bot2 for Peter Zijlstra wrote:
> > The following commit has been merged into the perf/core branch of tip:
> > 
> > Commit-ID:     90c91dfb86d0ff545bd329d3ddd72c147e2ae198
> > Gitweb:        https://git.kernel.org/tip/90c91dfb86d0ff545bd329d3ddd72c147e2ae198
> > Author:        Peter Zijlstra <peterz@...radead.org>
> > AuthorDate:    Thu, 05 Mar 2020 13:38:51 +01:00
> > Committer:     Peter Zijlstra <peterz@...radead.org>
> > CommitterDate: Fri, 20 Mar 2020 13:06:22 +01:00
> > 
> > perf/core: Fix endless multiplex timer
> > 
> > Kan and Andi reported that we fail to kill rotation when the flexible
> > events go empty, but the context does not. XXX moar
> > 
> > Fixes: fd7d55172d1e ("perf/cgroups: Don't rotate events for cgroups unnecessarily")
> 
> Can this patch (commit 90c91dfb86d0 ("perf/core: Fix endless multiplex
> timer") upstream) be applied to stable please? For PMU drivers built as
> modules, the bug can actually kill the system, since the runaway hrtimer
> loop keeps calling pmu->{enable,disable} after all the events have been
> closed and dropped their references to pmu->module. Thus legitimately
> unloading the module once things have got into this state quickly results in
> a crash when those callbacks disappear.
> 
> (FWIW I spent about two days fighting with this while testing a new driver
> as a module against the 5.3 kernel installed on someone else's machine,
> assuming it was a bug in my code...)

What exactly kernel(s) do you wish for it to be applied to?  It's
already in the latest stable releases of 5.7.y.

thanks,

greg k-h