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Howlett" , Christoph Lameter , David Rientjes , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Uladzislau Rezki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, maple-tree@lists.infradead.org, Alexei Starovoitov Subject: Re: [PATCH RFC v2 03/10] locking/local_lock: Introduce localtry_lock_t Message-ID: <20250217141956._01BcsrG@linutronix.de> References: <20250214-slub-percpu-caches-v2-0-88592ee0966a@suse.cz> <20250214-slub-percpu-caches-v2-3-88592ee0966a@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250214-slub-percpu-caches-v2-3-88592ee0966a@suse.cz> X-Rspam-User: X-Stat-Signature: ginkxn7mnnmsi3dhzug1dotwf8jgjksd X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 0025D40013 X-HE-Tag: 1739802001-377396 X-HE-Meta: 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 +19i2WQQ SiNj9J/hpfQWJoBICyLAiAa66kDA63S/iSX6dk6Bk0Ap0eeR9X61oDz1tH7srzZMrPTq1DdLvouoiGZiXdCFoJxeqvlHXohRRqcIdZcsXboc/mwMxxoqS61Vw+mXJKJ81t+2YwiBiS2Yr1wMRLtU8e6ck9R8ILEA7FHNxnLXRs13ZWYCkYcxbet8YvdDqCw8K+vcNDvkFDHi+dMYfcmO4yGfO0Tpc/UE942B4p6l2tkz0pUDj62LoJ/M4D0B47dNMRZVQ/1UKk0WozgWXPNn+zgwo4UtZoC/sYYb3aMs83Ajx8ccB7wOu9kEFFSWupxdy33ilq8ANfGhZik24nNeZqwKg5ji12XdvS+aZLl1RGIiGN+0ndvWkHHOEpQ== 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 2025-02-14 17:27:39 [+0100], Vlastimil Babka wrote: > From: Sebastian Andrzej Siewior > > In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect > critical section, but it doesn't prevent NMI, so the fully reentrant > code cannot use local_lock_irqsave() for exclusive access. > > Introduce localtry_lock_t and localtry_lock_irqsave() that > disables interrupts and sets acquired=1, so localtry_lock_irqsave() > from NMI attempting to acquire the same lock will return false. > > In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock(). > Map localtry_lock_irqsave() to preemptible spin_trylock(). > When in hard IRQ or NMI return false right away, since > spin_trylock() is not safe due to PI issues. spin_trylock() is not safe due to explicit locking in the underneath rt_spin_trylock() implementation. Removing this explicit locking and attempting only "trylock" is undesired due to PI implications. > Note there is no need to use local_inc for acquired variable, > since it's a percpu variable with strict nesting scopes. > > Signed-off-by: Sebastian Andrzej Siewior > Signed-off-by: Alexei Starovoitov > Signed-off-by: Vlastimil Babka Other than that, thank you two ;) Sebastian