On 2020-08-06 19:53, Greg KH wrote:
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@infradead.org AuthorDate: Thu, 05 Mar 2020 13:38:51 +01:00 Committer: Peter Zijlstra peterz@infradead.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.
Sorry, I implicitly meant 5.4.y there - the buggy commit was merged in 5.3, the fix in 5.7, so I think that's the only "stable" branch in between that warrants explicit action. Apologies if I'm getting the terminology wrong.
Cheers, Robin.