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AJvYcCWtrVU9nIJoLzF8BZB12ZHmOnsv1OtADQdkqiruve9/F3GwfGGRbiZWTAeim1pmY96r/UmTJagf4A==@kvack.org X-Gm-Message-State: AOJu0YwiFgXOW0n3HKWo79AV+fdfWLCozw9sBlTQLEzo5NW9A9MqJhOv x8L8KF2FU14s5BG/m054EK7ojGTOUx7lIr4963+3GHX7Tktqh3gjwKF0uKO5FiTp+lORGJRbUyi FQM0U5yPsObSLh1YFySDq8ziDpS0= X-Gm-Gg: ASbGnctvk7Qbl3lWxjv8JZx5CAKLQN5Co/T/3ph3bqaME8iBk97fHd265HWOBqh3Q/f CtT/5UMtUmJBxL9BoeGDwsqaQrOEYnXSgv3T5DxXQnBvx+wVw6Jz8sFGbgagKX+5laOS3R2mcjA apAwUCGXo4cScc X-Google-Smtp-Source: AGHT+IHhkiMm6MGXT17M9xfM7NM8mSv/O9ojIthPD9COWHkCQBAc+IHDA5g5Sf9lOqEzMmvYuHcqhE3bUTjjvjqFZhY= X-Received: by 2002:a5d:6c63:0:b0:38f:4b2c:2475 with SMTP id ffacd0b85a97d-38f4b2c255amr6762956f8f.20.1739904079217; Tue, 18 Feb 2025 10:41:19 -0800 (PST) MIME-Version: 1.0 References: <20250214-slub-percpu-caches-v2-0-88592ee0966a@suse.cz> <20250214-slub-percpu-caches-v2-3-88592ee0966a@suse.cz> <20250217141956._01BcsrG@linutronix.de> In-Reply-To: From: Alexei Starovoitov Date: Tue, 18 Feb 2025 10:41:08 -0800 X-Gm-Features: AWEUYZkw7pLuqM8rpwQ14Nm2IrYgdo2AXxznTsMF9KECxxoRCxM2XTApIligPx4 Message-ID: Subject: Re: [PATCH RFC v2 03/10] locking/local_lock: Introduce localtry_lock_t To: Vlastimil Babka Cc: Sebastian Andrzej Siewior , Suren Baghdasaryan , "Liam R. Howlett" , Christoph Lameter , David Rientjes , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Uladzislau Rezki , linux-mm , LKML , rcu@vger.kernel.org, maple-tree@lists.infradead.org, Alexei Starovoitov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 724C61C0021 X-Stat-Signature: geu5eg69o9hi3njmdryyo8n8yocay3tc X-Rspam-User: X-HE-Tag: 1739904081-958496 X-HE-Meta: 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 yB7l25ul qlp0ZwuqgQaHq37muOUVm7NXqcAXpOZIcozStNrd9vQW6lmZ3LI1H5FSeTG9rEobgQhaV6rlnhPLkUiGZWVatwk3gkDnp+JTM+1FaRd5KeLs0di4l7LEODG2Dcq3+PvYk4kzGXKtCnFk3gOPGQ2zftdW7idOFo5KdZ+foDpIFZSrtm/ZuHv1Ix4VMWNS+g2CqR2Dxy4tNuYdXy13yu4SROnmlCwbmxpHkCaETXumQI8bWlLUlKIsPayczTPrrwgNvFZJCINRWslTQ6QpooHE5b0U9W3k/999bGrdBbK2DmTpMe3MkyFfWNSxKSggvkivLQxGfo/rHrIVQF9CZDySkOKddQ1nKwYbvmXh39Vb695NTuc4pDDtPzG6GXp4dmiU7OMgyY24eYMBND90ZXflXGW3KYFdAdClPlWm9aT2S6RUsyqGwuB1O6FWsPi9aoZ6P6b+vsbAwY5lfVxzTS/ZcA4v+7A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.001961, 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 Mon, Feb 17, 2025 at 6:35=E2=80=AFAM Vlastimil Babka wr= ote: > > On 2/17/25 15:19, Sebastian Andrzej Siewior wrote: > > 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=3D1, 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. Makes sense. > Just to be sure, you're suggesting how to reword that sentence in the > changelog to make it more precise right? > Alexei will you incorporate that in your version? Sure. Let's squash patches 3 and 4 and add above commit log clarification. Whoever respins first can do it.