Messages in this thread | | | Date | Wed, 10 Feb 2021 13:00:25 -0500 | From | Sasha Levin <> | Subject | Re: [stable 4.4, 4.9, 4.14, 4.19 LTS] Missing fix "memcg: fix a crash in wb_workfn when a device disappears" |
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On Wed, Feb 10, 2021 at 12:25:31PM -0500, Mathieu Desnoyers wrote: >----- On Feb 10, 2021, at 12:09 PM, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote: > >> On Wed, Feb 10, 2021 at 11:04:19AM -0500, Mathieu Desnoyers wrote: >>> Hi, >>> >>> While reconciling the lttng-modules writeback instrumentation with its >>> counterpart >>> within the upstream Linux kernel, I notice that the following commit introduced >>> in >>> 5.6 is present in stable branches 5.4 and 5.5, but is missing from LTS stable >>> branches >>> for 4.4, 4.9, 4.14, 4.19: >>> >>> commit 68f23b89067fdf187763e75a56087550624fdbee >>> ("memcg: fix a crash in wb_workfn when a device disappears") >>> >>> Considering that this fix was CC'd to the stable mailing list, is there any >>> reason why it has not been integrated into those LTS branches ? >> >> Yes, it doesn't apply at all. If you think this is needed, I will >> gladly take backported and tested patches. >> >> But why do you think this is needed in older kernels? Have you hit >> this in real-life? > >No, I have not hit this in real-life. Looking at the patch commit message, >the conditions needed to trigger this issue are very specific: memcg must >be enabled, and a device must be hotremoved while writeback is going on, >with writeback tracing active. > >AFAIU memcg was present in those LTS releases and devices can be hotremoved >(please correct me if I'm wrong here), so all the preconditions appear to be >met. > >Considering that I don't have the setup ready to reproduce this issue, I will >have to defer to the original patch authors for a properly tested backport, >if it happens to be relevant at all. > >I just though reporting what appears to be a missing fix in LTS branches >would be the right thing to do.
Looks like it doesn't apply due to churn with tracepoints, I think it's fixable. Let me try and get something for <=4.19.
-- Thanks, Sasha
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