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Fri, 13 Mar 2026 06:53:41 -0400 (EDT) Message-ID: Date: Fri, 13 Mar 2026 03:53:40 -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 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 From: "Barry K. Nathan" In-Reply-To: <88e4edea-f204-4f06-b898-2995237fc823@w6rz.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit (I forgot to add Francesco Dolcini as a recipient on my previous email, so I'm doing that now.) 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. -- -Barry K. Nathan