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Thu, 13 Feb 2025 15:03:56 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id dsArK9wJrmfGdAAAD6G6ig (envelope-from ); Thu, 13 Feb 2025 15:03:56 +0000 Message-ID: <1fda7391-228d-4e10-8449-189be36eb27c@suse.cz> Date: Thu, 13 Feb 2025 16:03:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t To: Alexei Starovoitov , bpf@vger.kernel.org Cc: andrii@kernel.org, memxor@gmail.com, akpm@linux-foundation.org, peterz@infradead.org, bigeasy@linutronix.de, rostedt@goodmis.org, houtao1@huawei.com, hannes@cmpxchg.org, shakeel.butt@linux.dev, mhocko@suse.com, willy@infradead.org, tglx@linutronix.de, jannh@google.com, tj@kernel.org, linux-mm@kvack.org, kernel-team@fb.com References: <20250213033556.9534-1-alexei.starovoitov@gmail.com> <20250213033556.9534-4-alexei.starovoitov@gmail.com> Content-Language: en-US From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: C47821C000F X-Stat-Signature: se9y4zrimmeuzpa8mskcn3dk5ijsc8sr X-HE-Tag: 1739459048-892585 X-HE-Meta: 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 5iEd7x8i UvZjQtbQArHs94S2HGl15pLNj0eZvjXM0EnQpM3teJsnVw3le2UCtz5lY7LnjUAy4ckSlkh0K042YyZGBbETOlXDqZ4AJ5gEgYsscuC4WisELkgt63VM4CA5Q4sJkM2Us5wXL58Hrs/BurzKcznPIoeyWUPKtXodgDn8GrRUpcbYkHG3IIE86UcJQ4U8nICmXmXv7B5vYDf7cCajErzU8qw+y861C0ixqheyK4fnu1EpLQb1o/r4u+034vK4Th2T0wX7mtm4hq6s6WqJgWjgifKPXnfpa8prwBt6c7AbjBe21pBlYEWammd5DbgVWSDf9/rC4ftoFl3xlaEMmRIgD8gfdG3IS1210EDZ9OHITyQWDykdFeV2KY+VzR3jXBxis7K5vv4PJsSUli2BhI/bJk9o6QTtNqCsVYh1hLhc8Pe2bQoJi9oSRM/sjmg== 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 2/13/25 04:35, Alexei Starovoitov 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. > > 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 > --- > include/linux/local_lock.h | 59 +++++++++++++ > include/linux/local_lock_internal.h | 123 ++++++++++++++++++++++++++++ > 2 files changed, 182 insertions(+) > > diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h > index 091dc0b6bdfb..05c254a5d7d3 100644 > --- a/include/linux/local_lock.h > +++ b/include/linux/local_lock.h > @@ -51,6 +51,65 @@ > #define local_unlock_irqrestore(lock, flags) \ > __local_unlock_irqrestore(lock, flags) > > +/** > + * localtry_lock_init - Runtime initialize a lock instance > + */ > +#define localtry_lock_init(lock) __localtry_lock_init(lock) > + > +/** > + * localtry_lock - Acquire a per CPU local lock > + * @lock: The lock variable > + */ > +#define localtry_lock(lock) __localtry_lock(lock) > + > +/** > + * localtry_lock_irq - Acquire a per CPU local lock and disable interrupts > + * @lock: The lock variable > + */ > +#define localtry_lock_irq(lock) __localtry_lock_irq(lock) > + > +/** > + * localtry_lock_irqsave - Acquire a per CPU local lock, save and disable > + * interrupts > + * @lock: The lock variable > + * @flags: Storage for interrupt flags > + */ > +#define localtry_lock_irqsave(lock, flags) \ > + __localtry_lock_irqsave(lock, flags) > + > +/** > + * localtry_trylock_irqsave - Try to acquire a per CPU local lock, save and disable > + * interrupts if acquired > + * @lock: The lock variable > + * @flags: Storage for interrupt flags > + * > + * The function can be used in any context such as NMI or HARDIRQ. Due to > + * locking constrains it will _always_ fail to acquire the lock on PREEMPT_RT. The "always fail" applies only to the NMI and HARDIRQ contexts, right? It's not entirely obvious so it sounds worse than it is. > + > +#define __localtry_trylock_irqsave(lock, flags) \ > + ({ \ > + int __locked; \ > + \ > + typecheck(unsigned long, flags); \ > + flags = 0; \ > + if (in_nmi() | in_hardirq()) { \ > + __locked = 0; \ Because of this, IIUC? > + } else { \ > + migrate_disable(); \ > + __locked = spin_trylock(this_cpu_ptr((lock))); \ > + if (!__locked) \ > + migrate_enable(); \ > + } \ > + __locked; \ > + }) > + > #endif /* CONFIG_PREEMPT_RT */