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Fri, 13 Mar 2026 09:38:26 -0400 (EDT) Message-ID: <71d1fa5b-e6bb-4289-bd8d-445aeddcb9d8@pobox.com> Date: Fri, 13 Mar 2026 06:38:25 -0700 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: freeze during boot regression Re: [PATCH 6.12 000/265] 6.12.77-rc1 review From: "Barry K. Nathan" To: Ron Economos , Greg Kroah-Hartman , stable@vger.kernel.org Cc: patches@lists.linux.dev, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, linux@roeck-us.net, shuah@kernel.org, patches@kernelci.org, lkft-triage@lists.linaro.org, pavel@nabladev.com, jonathanh@nvidia.com, f.fainelli@gmail.com, sudipm.mukherjee@gmail.com, rwarsow@gmx.de, conor@kernel.org, hargar@microsoft.com, broonie@kernel.org, achill@achill.org, sr@sladewatkins.com, Francesco Dolcini References: <20260312201018.128816016@linuxfoundation.org> <2a313336-ccfc-42b7-a14d-c116733ef64a@w6rz.net> <1c54210a-e197-4eb9-88b5-2ed2589c7230@pobox.com> <88e4edea-f204-4f06-b898-2995237fc823@w6rz.net> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/13/26 03:53, Barry K. Nathan wrote: [snip] > On 3/13/26 02:37, Ron Economos wrote: >> On 3/13/26 01:05, Barry K. Nathan wrote: >>> On 3/12/26 23:10, Ron Economos wrote: >>>> Probably those sched/fair patches. >>> >>> Yes, after bisecting it turned out to be >>> sched-fair-fix-eevdf-entity-placement-bug-causing-sc.patch >>> >>> Taking 6.12.77-rc1 and reverting both of the sched-fair patches >>> results in a working kernel that boots consistently (which I am >>> using now to send this email). >> >> Confirmed on RISC-V. Reverting "sched/fair: Fix lag clamp" commit b547745a2c78fd1cc1fdc6a0d1b05c884c05cec2 and "sched/fair: Fix EEVDF entity placement bug causing scheduling lag" commit f9891a33ba67ce40e5a17023d2f3a5e2b7d72ffd resolves the issue. > > After looking into it a bit more, I found two upstream commits that > should fix this issue without reverting the two sched/fair patches > (either of the two commits alone should fix it if I understand > the bug and the code correctly): > > > commit 4423af84b29794a9bd2bd07188d8e71083e54c61 > sched/fair: optimize the PLACE_LAG when se->vlag is zero > > commit c70fc32f44431bb30f9025ce753ba8be25acbba3 > sched/fair: Adhere to place_entity() constraints > > > I think c70fc32f4443 is theoretically the proper fix, while > 4423af84b297 is a performance optimization that just happens to also > fix the bug. > > 4423af84b297 turned out to be the easier backport; the upstream patch > applies to 6.12.77-rc1 with an offset but no fuzz or conflicts. So I > tried 6.12.77-rc1 + 4423af84b297, and just as with reverting the two > sched/fair patches, it eliminates the boot freeze in my testing. It's > what I'm running now as I write and send this email. > > Next, I think I'll try doing a backport of c70fc32f4443 (I think it > should be easy enough), and I'll try testing 6.12.77-rc1 + > c70fc32f4443 (probably both with and without 4423af84b297). > Maybe 4423af84b297 on its own is enough though. I originally wrote a much longer email, but I'll try to keep this concise. I was able to backport c70fc32f4443 successfully, and the backport does fix the reboot freezes (with or without 4423af84b297). However, backporting that commit convinced me that it's too risky; I'm particularly worried it could make future sched/fair backports more difficult. And once 4423af84b297 is applied, I think c70fc32f4443 ends up being a fix for a theoretical bug. So, even though c70fc32f4443 is the commit that was cc'd to stable@, I believe 4423af84b297 is a better (safer, less risky) way to go. In summary, I believe the two best ways to fix this regression are: 1. Backport 4423af84b297, or 2. Revert the two sched/fair patches. -- -Barry K. Nathan