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Fri, 20 Dec 2024 19:42:15 -0800 (PST) Received: from localhost ([240f:74:7be:1:3630:b0a:8446:1dba]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72aad8fb8adsm3975542b3a.143.2024.12.20.19.42.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Dec 2024 19:42:15 -0800 (PST) Date: Sat, 21 Dec 2024 12:42:13 +0900 From: Koichiro Den To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] vmstat: disable vmstat_work on vmstat_cpu_down_prep() Message-ID: <5eiatywyiv2izxy4crbzxzexizjenx6wbvzlp2l3hbvf2m3ug5@2uyvmr4v2ix7> References: <20241220134234.3809621-1-koichiro.den@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241220134234.3809621-1-koichiro.den@canonical.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 61C4840007 X-Stat-Signature: 3hzqbt879tub4ymz13m7newomgajx6te X-Rspam-User: X-HE-Tag: 1734752513-230123 X-HE-Meta: U2FsdGVkX19U4s1VbD8ivd4x1B57PzMiE1mDnLGeRRZZYGyYxpv2eGZD+P6nWt1k3Zu8doOJXIcnEhLEd8m7/Y6Px03ZT+xf2h62Gj86wNLuMVzCQQ19nbjX7MF8Wprpq2CFcIY/8VDdKQQv3PtiCVvfI1W9KiPrQxHThZFu8DbpO3hZsjBsSwoKYvN/IxEaxvdVBORDm/C8CwCYv7ObGr7UYDJHc1Sl8XHa3w+R9BnUQh3LGj8WWOmxSCdvosebWB5PH4TwIKR1CosDfxdlmlosJ3BjsCkr5TcJ1Qpps/UYbOrqgG1jxsxma7kadhXSR9z28eF6a1UFjlkQQmVMUTpMb/WmjlXd5EWvypZwt1zm423cguR7s91jT+9Vz30lZXO7039JkBOeEMiSl8uEstlmt2Q0XUD4BtAo2oZ87Yodj8BWs6tMe4LhbLTiiXjxcUoQO/LUSpxPEvK/iHu6y9SonPQecSgFC5y2orNmpm9OnHQg3W9BL3qDTtpGl/aaKNblI5V+2MUdTpuh4ssu7BlmA4com6euzm6eP1D/TcYY5Wi9xIBpDInO5dBsTXwVV8uJkSkpDv8qsGxmoJlo1NLJbj+hwM5MJSEZlQG+ZIAqOLLjSm/jLgWbpigR4S64R3jrtHAQikCrNxJMnDMnckOsQuDKzwz9MpU4uVrlSYdftGCXGmoVvmYQSIiYIzjz3NZ+2NDuP9o6E/mA9TKB9LfzK7W2/CtuYjlGM6SNOy0mYhPlaP91bDDWSxCAVX03o41eC6Xdza1E13sOtmNegrqyRDeIOdktsTIADgbl8p7zSWy+ScdLXKJ6toCicYpnifg+aRifHyDR8styfJh9lWQX8HHz5QR85j6PBLoeiw2eiftvuHRlkEcZLJD/irTMUSPHF/JDA+J1xyGTrvOSN/0BdKJnWZx92Fx3eQu+3aBwRWgZTPC0KAxIG71Xeky1jjaxUZ0aBoxJkcvEkqO mImb1Rxk 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.009420, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Dec 20, 2024 at 10:42:34PM +0900, Koichiro Den wrote: > Even after mm/vmstat:online teardown, shepherd may still queue work for > the dying cpu until the cpu is removed from online mask. While it's > quite rare, this means that after unbind_workers() unbinds a per-cpu > kworker, it potentially runs vmstat_update for the dying CPU on an > irrelevant cpu before entering STARTING section. > When CONFIG_DEBUG_PREEMPT=y, it results in the following error with the > backtrace. > > BUG: using smp_processor_id() in preemptible [00000000] code: \ > kworker/7:3/1702 > caller is refresh_cpu_vm_stats+0x235/0x5f0 > CPU: 0 UID: 0 PID: 1702 Comm: kworker/7:3 Tainted: G > Tainted: [N]=TEST > Workqueue: mm_percpu_wq vmstat_update > Call Trace: > > dump_stack_lvl+0x8d/0xb0 > check_preemption_disabled+0xce/0xe0 > refresh_cpu_vm_stats+0x235/0x5f0 > vmstat_update+0x17/0xa0 > process_one_work+0x869/0x1aa0 > worker_thread+0x5e5/0x1100 > kthread+0x29e/0x380 > ret_from_fork+0x2d/0x70 > ret_from_fork_asm+0x1a/0x30 > > > So, disable vmstat_work reliably on vmstat_cpu_down_prep(). > > Signed-off-by: Koichiro Den > --- > mm/vmstat.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 4d016314a56c..44e1d87dcf01 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -2154,7 +2154,7 @@ static int vmstat_cpu_online(unsigned int cpu) > > static int vmstat_cpu_down_prep(unsigned int cpu) > { > - cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu)); > + disable_delayed_work_sync(&per_cpu(vmstat_work, cpu)); > return 0; > } > > -- Andrew, I just noticed my silly mistake - I needed to enable the work in the opposite direction. It looks like you've already queued this (v1) to mm-hotfixes-unstable. Could you please replace it with v2? (https://lore.kernel.org/all/20241221033321.4154409-1-koichiro.den@canonical.com/) Sorry to bother you. Let me know if submitting a separate follow-up patch would be more appropriate. Thank you. -Koichiro Den