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Mon, 17 Feb 2025 14:35:11 +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 mK7GIx9Js2dlJgAAD6G6ig (envelope-from ); Mon, 17 Feb 2025 14:35:11 +0000 Message-ID: Date: Mon, 17 Feb 2025 15:35:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 03/10] locking/local_lock: Introduce localtry_lock_t Content-Language: en-US To: Sebastian Andrzej Siewior Cc: Suren Baghdasaryan , "Liam R. 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 References: <20250214-slub-percpu-caches-v2-0-88592ee0966a@suse.cz> <20250214-slub-percpu-caches-v2-3-88592ee0966a@suse.cz> <20250217141956._01BcsrG@linutronix.de> 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+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <20250217141956._01BcsrG@linutronix.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Queue-Id: 7FFC640013 X-Rspamd-Server: rspam07 X-Stat-Signature: mssehtu9mxhp59paue99tcbp7o9doopu X-HE-Tag: 1739802913-626130 X-HE-Meta: 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 0nxlgrA2 70gOMSXgUrUVmSiwwTgPr7My995CJ10/nU5pqzqgfm2PMEQf7mDt1MJ/h3W0VO5XSU5bPPQYB8zZ/3w8wshdtf/xHD71dzgQ72wwLHyabKt6rKRqqHpgvLfJ9AfAM2CrYdrE5/KvcWgPXLh9Ers0uJ1tQiyE48pawIPFTi/+TcS/teF+h5NUYCbr9n3LImHzoPJmqFsafTWOevGCG+TeAMLt4N3/GIm29m5OhlP2hmAyMXBv8Y3CYdXeazF/rXfNj7E/vqaUdhI9VIQMwHCl+AroC0ADfplzcj5EiLph0KUzGMxDO585Ylt6h90ikREGIP+Tlbe8QaQ5hJl51LYIUdpRnZLyqt6WtW6goZhqcetIg8iQKYFCBNqTi8aWcVKnp+aJOB9fO67FoSMkIuvLhV8jZzW2EUM6JuceXCouUd8Wcbth8YonPH499Fyp1NTAG44rufIHAh0QJ3gfDAS2ojKuZqA== 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 2/17/25 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=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. 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? >> 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 ;) Thank you too :) Do you agree with my fixups and addition here? https://lore.kernel.org/all/efc30cf9-8351-4889-8245-cc4a6893ebf4@suse.cz/ > Sebastian