From: Sasha Levin <sashal@kernel.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
stable <stable@vger.kernel.org>, Theodore Tso <tytso@mit.edu>,
linux-kernel <linux-kernel@vger.kernel.org>,
Chris Mason <clm@fb.com>, Tejun Heo <tj@kernel.org>,
Jens Axboe <axboe@kernel.dk>, rostedt <rostedt@goodmis.org>,
Michael Jeanson <mjeanson@efficios.com>
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"
Date: Wed, 10 Feb 2021 13:00:25 -0500 [thread overview]
Message-ID: <20210210180025.GE4035784@sasha-vm> (raw)
In-Reply-To: <2071967108.15704.1612977931149.JavaMail.zimbra@efficios.com>
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
next prev parent reply other threads:[~2021-02-10 18:11 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-10 16:04 [stable 4.4, 4.9, 4.14, 4.19 LTS] Missing fix "memcg: fix a crash in wb_workfn when a device disappears" Mathieu Desnoyers
2021-02-10 17:09 ` Greg KH
2021-02-10 17:25 ` Mathieu Desnoyers
2021-02-10 18:00 ` Sasha Levin [this message]
2021-02-10 18:30 ` Sasha Levin
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