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From: Shakeel Butt To: "Vlastimil Babka (SUSE)" Cc: Sebastian Andrzej Siewior , Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [PATCH v2] memcg: Remove the lockdep assert from __mod_objcg_mlstate(). Message-ID: References: <20240528121928.i-Gu7Jvg@linutronix.de> <09e085bb-f09e-4901-a2dd-a0b789bb8a4d@kernel.org> <20240528134027.OxDASsS3@linutronix.de> <20240528141341.rz_rytN_@linutronix.de> <897354c6-764b-4f3f-9ece-2feafb0222e9@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <897354c6-764b-4f3f-9ece-2feafb0222e9@kernel.org> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: F30C04000D X-Stat-Signature: 65p9xphhekaaoxb6yibapw6waia188re X-HE-Tag: 1716913287-925587 X-HE-Meta: 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 Oz1fbDCc b3nwPg8syH8UZe0iqyNcSYqmLaxhxfWnADbbgrMngtiBLpL/5YZhKtOMm/KUrvEMAiVaroJyDTXSW549Q9A/iwVwzju7Y/8enSTj329dYdaVRVnejzSEWJIV5d4x7YanSi1ZU X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Tue, May 28, 2024 at 05:07:06PM GMT, Vlastimil Babka (SUSE) wrote: > On 5/28/24 4:59 PM, Shakeel Butt wrote: > > On Tue, May 28, 2024 at 04:13:41PM GMT, Sebastian Andrzej Siewior wrote: > >> The assert was introduced in the commit cited below as an insurance that > >> the semantic is the same after the local_irq_save() has been removed and > >> the function has been made static. > >> > >> The original requirement to disable interrupt was due the modification > >> of per-CPU counters which require interrupts to be disabled because the > >> counter update operation is not atomic and some of the counters are > >> updated from interrupt context. > >> > >> All callers of __mod_objcg_mlstate() acquire a lock > >> (memcg_stock.stock_lock) which disables interrupts on !PREEMPT_RT and > >> the lockdep assert is satisfied. On PREEMPT_RT the interrupts are not > >> disabled and the assert triggers. > >> > >> The safety of the counter update is already ensured by > >> VM_WARN_ON_IRQS_ENABLED() which is part of __mod_memcg_lruvec_state() and > >> does not require yet another check. > > > > One question on VM_WARN_ON_IRQS_ENABLED() in __mod_memcg_lruvec_state(). > > On a PREEMPT_RT kernel with CONFIG_DEBUG_VM, will that > > VM_WARN_ON_IRQS_ENABLED() cause a splat or VM_WARN_ON_IRQS_ENABLED is > > special on PREEMPT_RT kernels? > > It only does something with CONFIG_DEBUG_VM_IRQSOFF and that's disabled by > dependencies on PREEMPT_RT :) Thanks for the explanation.