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Wed, 11 Dec 2024 10:53:11 +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 SK4HExdvWWezZQAAD6G6ig (envelope-from ); Wed, 11 Dec 2024 10:53:11 +0000 Message-ID: <1c760bf1-14a4-42e4-a55b-438a29987aef@suse.cz> Date: Wed, 11 Dec 2024 11:53:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v2 3/6] locking/local_lock: Introduce local_trylock_irqsave() Content-Language: en-US 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, tj@kernel.org, linux-mm@kvack.org, kernel-team@fb.com References: <20241210023936.46871-1-alexei.starovoitov@gmail.com> <20241210023936.46871-4-alexei.starovoitov@gmail.com> 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-Rspamd-Queue-Id: D70C71A0002 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: buscnt98ysn4ssa386cckrott7ude77o X-HE-Tag: 1733914368-549427 X-HE-Meta: U2FsdGVkX196IKN0Ki31BMioDoybY+gyYLi8yIA2VE8g72QqNfxFmsr0/fN3yxD7c2FIjcAzn0nObTD53a/VnGo118qOywxMLsTVQs1zyk2BRDSCOXliBJli0IcYFBCMOjkVwIaF2wH/shNsVUuUhFcdXpKxldaDjZQ4OiqREpFXDMN9bUzecwRmhia/k2Y76tU/KsgtZH0/eDeP4WYz8jO2PseaAkDPiPvqYhCVIuJmhEk9BUyy59r7y0362mtlmI9kJpr/gkP444KskYiLWtaAtYedp1hgR+303udD0xE27gQRTu6cSPgM+PlIfIkoELqbbN7O6dpsXKx1ZT0I0DQ13RlvnZgaNTb1AlRypRG94OvqYHHxllyhOVshZEgYn+OvJRQjLa8vnup+NQfO/WaedJQKdVXZOPiuz5K1+pLcmh5OefuXh/lOWNRD58UAGCjknGSEPWcJamAKQxwHghPSFa94uDDcTh46u7nZJ9jW0Ew8Scwu9mgImnvCdaamHWrRN0iSsMmEOOywkwvsW+Z1MsG3vmOVNDYT+75E/JZgHAfzmkD9NI34uMFiT9RrfhPdMC+3qGqNOY/nRIedVrDAep/B8P64MMspwq2sW1XqBGHNDNhNoSy7tZXLUIideAGcJVqKZRS0cMsJFnbL6wkUkgiq2Z/U+ySB9jVqOv75U03epdIhUV5v0SiJK/6CzBpsHV9lEfh8VqF3E9uDWGlBK67j2ShX/Tn1b8/hX26sO7CAN3WT7QlaamTzk9QZm5k5S4zyl0y5AbFyiu/wbFja0zSr+wZOujSw+kgcWDsGvbUuk98aCzSabaBfMagOqIWayK9KIHyQkFlj/T0Zqz1Y4E4pHgqxFHLV3PN/9XwUnDhXcXqNYeuVSu2uKErHlXoNx+FNzedv/deP7s+JUVa85iCIuQFcKyrFR2pfZNJkPssN9hXKo3kDSNGkk2tCMZaYHO/4VTaZzAwxgF8 LRsLrbRG ZxokcZGWnM45vQA9KdoOtRIYN/34wt1pTgmtq5tMvQzKIDmPiZtvDQsL9yvl/K9HIvD3JDC19ivSCRNbdkadY/uVqquiFBMx07E7On9hbGWSG6DNo9tUaz9BzzlA2XfcGjld+2NIorjaAIgwjmSAQ8w0lZYNGyz/VJ6ekT6/jEvKZqhRcz3l03v3dPMXzdnTpqFi9d9ke+SDX+rZ0xDMs9pehSp94z0D8/ux7VfHpg/uc3qNaXshP0eP02eTbU9Jgj5keqe9UKm0nNzZxzt2Gc0egG4GCRxlNwQEnLjUQhMWxbDKpb8er4JuKmJfeputbCL1sKYALgwJlFmhzGMM/Ro119ORmAhEo5mr3XN3CngpHVi02sya4hdTOyP2keIbbrYaWZ5osytDexxnDb9RMii19TPEzTe7o5XWD3sPxppiZ1+pasv0qSGl00g== 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 12/10/24 03:39, Alexei Starovoitov wrote: > From: Alexei Starovoitov > > Similar to local_lock_irqsave() introduce local_trylock_irqsave(). > It uses spin_trylock in PREEMPT_RT and always succeeds when !RT. Hmm but is that correct to always succeed? If we're in an nmi, we might be preempting an existing local_(try)lock_irqsave() critical section because disabling irqs doesn't stop NMI's, right? > Signed-off-by: Alexei Starovoitov > --- > include/linux/local_lock.h | 9 +++++++++ > include/linux/local_lock_internal.h | 23 +++++++++++++++++++++++ > 2 files changed, 32 insertions(+) > > diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h > index 091dc0b6bdfb..6880c29b8b98 100644 > --- a/include/linux/local_lock.h > +++ b/include/linux/local_lock.h > @@ -30,6 +30,15 @@ > #define local_lock_irqsave(lock, flags) \ > __local_lock_irqsave(lock, flags) > > +/** > + * local_trylock_irqsave - Try to acquire a per CPU local lock, save and disable > + * interrupts. Always succeeds in !PREEMPT_RT. > + * @lock: The lock variable > + * @flags: Storage for interrupt flags > + */ > +#define local_trylock_irqsave(lock, flags) \ > + __local_trylock_irqsave(lock, flags) > + > /** > * local_unlock - Release a per CPU local lock > * @lock: The lock variable > diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h > index 8dd71fbbb6d2..2c0f8a49c2d0 100644 > --- a/include/linux/local_lock_internal.h > +++ b/include/linux/local_lock_internal.h > @@ -31,6 +31,13 @@ static inline void local_lock_acquire(local_lock_t *l) > l->owner = current; > } > > +static inline void local_trylock_acquire(local_lock_t *l) > +{ > + lock_map_acquire_try(&l->dep_map); > + DEBUG_LOCKS_WARN_ON(l->owner); > + l->owner = current; > +} > + > static inline void local_lock_release(local_lock_t *l) > { > DEBUG_LOCKS_WARN_ON(l->owner != current); > @@ -45,6 +52,7 @@ static inline void local_lock_debug_init(local_lock_t *l) > #else /* CONFIG_DEBUG_LOCK_ALLOC */ > # define LOCAL_LOCK_DEBUG_INIT(lockname) > static inline void local_lock_acquire(local_lock_t *l) { } > +static inline void local_trylock_acquire(local_lock_t *l) { } > static inline void local_lock_release(local_lock_t *l) { } > static inline void local_lock_debug_init(local_lock_t *l) { } > #endif /* !CONFIG_DEBUG_LOCK_ALLOC */ > @@ -91,6 +99,13 @@ do { \ > local_lock_acquire(this_cpu_ptr(lock)); \ > } while (0) > > +#define __local_trylock_irqsave(lock, flags) \ > + ({ \ > + local_irq_save(flags); \ > + local_trylock_acquire(this_cpu_ptr(lock)); \ > + 1; \ > + }) > + > #define __local_unlock(lock) \ > do { \ > local_lock_release(this_cpu_ptr(lock)); \ > @@ -148,6 +163,14 @@ typedef spinlock_t local_lock_t; > __local_lock(lock); \ > } while (0) > > +#define __local_trylock_irqsave(lock, flags) \ > + ({ \ > + typecheck(unsigned long, flags); \ > + flags = 0; \ > + migrate_disable(); \ > + spin_trylock(this_cpu_ptr((__lock))); \ > + }) > + > #define __local_unlock(__lock) \ > do { \ > spin_unlock(this_cpu_ptr((__lock))); \