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Fri, 11 Jul 2025 09:55:23 +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 UMntCIvfcGhedQAAD6G6ig (envelope-from ); Fri, 11 Jul 2025 09:55:23 +0000 Message-ID: <1adbee35-6131-49de-835b-2c93aacfdd1e@suse.cz> Date: Fri, 11 Jul 2025 11:55:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/6] locking/local_lock: Introduce local_lock_lockdep_start/end() To: Sebastian Andrzej Siewior , Alexei Starovoitov Cc: bpf@vger.kernel.org, linux-mm@kvack.org, harry.yoo@oracle.com, shakeel.butt@linux.dev, mhocko@suse.com, andrii@kernel.org, memxor@gmail.com, akpm@linux-foundation.org, peterz@infradead.org, rostedt@goodmis.org, hannes@cmpxchg.org References: <20250709015303.8107-1-alexei.starovoitov@gmail.com> <20250709015303.8107-4-alexei.starovoitov@gmail.com> <20250711075001.fnlMZfk6@linutronix.de> Content-Language: en-US From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <20250711075001.fnlMZfk6@linutronix.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Action: no action X-Rspamd-Queue-Id: 4251EC000D X-Stat-Signature: cguio8oknpadikrowierkzq5wum6mo73 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1752227725-67102 X-HE-Meta: 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 xnZAGGqT 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 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 7/11/25 09:50, Sebastian Andrzej Siewior wrote: > On 2025-07-08 18:53:00 [-0700], Alexei Starovoitov wrote: >> From: Alexei Starovoitov >> >> Introduce local_lock_lockdep_start/end() pair to teach lockdep >> about a region of execution where per-cpu local_lock is not taken >> and lockdep should consider such local_lock() as "trylock" to >> avoid multiple false-positives: >> - lockdep doesn't like when the same lock is taken in normal and >> in NMI context >> - lockdep cannot recognize that local_locks that protect kmalloc >> buckets are different local_locks and not taken together >> >> This pair of lockdep aid is used by slab in the following way: >> >> if (local_lock_is_locked(&s->cpu_slab->lock)) >> goto out; >> local_lock_lockdep_start(&s->cpu_slab->lock); >> p = ___slab_alloc(s, gfpflags, node, addr, c, orig_size); >> local_lock_lockdep_end(&s->cpu_slab->lock); >> >> Where ___slab_alloc() is calling >> local_lock_irqsave(&s->cpu_slab->lock, ...) many times, >> and all of them will not deadlock since this lock is not taken. > > So you prefer this instead of using a trylock variant in ___slab_alloc() > which would simply return in case the trylock fails? The code isn't always in a position to "simply return". On !RT I think we can at least assume that if we succeeded once, it means we're not a irq/nmi interrupting a locked context so we'll succeed the following attempts too. On RT IIUC the lock might be taken by someone else, so a trylock might fail (even if it should also mean we're in a context that can do a non-try lock). > Having the local_lock_is_locked() is still good to avoid the lock > failure if it can be detected early. I am just not sure if the extra > lockdep override is really needed. > > … >> --- a/include/linux/local_lock.h >> +++ b/include/linux/local_lock.h >> @@ -81,6 +81,21 @@ >> #define local_trylock_irqsave(lock, flags) \ >> __local_trylock_irqsave(lock, flags) >> >> +#ifdef CONFIG_DEBUG_LOCK_ALLOC >> +#define local_lock_lockdep_start(lock) \ >> + do { \ >> + lockdep_assert(!__local_lock_is_locked(lock)); \ >> + this_cpu_ptr(lock)->dep_map.flags = LOCAL_LOCK_UNLOCKED;\ >> + } while (0) >> + >> +#define local_lock_lockdep_end(lock) \ >> + do { this_cpu_ptr(lock)->dep_map.flags = 0; } while (0) >> + >> +#else >> +#define local_lock_lockdep_start(lock) /**/ >> +#define local_lock_lockdep_end(lock) /**/ > > Why the /**/? > > … >> index 9f361d3ab9d9..6c580081ace3 100644 >> --- a/include/linux/lockdep_types.h >> +++ b/include/linux/lockdep_types.h >> @@ -190,13 +190,15 @@ struct lockdep_map { >> u8 wait_type_outer; /* can be taken in this context */ >> u8 wait_type_inner; /* presents this context */ >> u8 lock_type; >> - /* u8 hole; */ >> + u8 flags; >> #ifdef CONFIG_LOCK_STAT >> int cpu; >> unsigned long ip; >> #endif >> }; >> >> +#define LOCAL_LOCK_UNLOCKED 1 > > Maybe DEPMAP_FLAG_LL_UNLOCKED so it is kind of obvious where it belongs > to. Maybe use "u8 local_lock_unlocked:1;" instead the flags + define. It > is even used for held_lock below so it is not a new concept with > lockdep. It would narrow down the usage. > >> struct pin_cookie { unsigned int val; }; >> > > Sebastian