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Fri, 11 Jul 2025 15:56:34 +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 FBdqMDI0cWhEbwAAD6G6ig (envelope-from ); Fri, 11 Jul 2025 15:56:34 +0000 Message-ID: Date: Fri, 11 Jul 2025 17:56:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/percpu: prevent concurrency problem for pcpu_nr_populated read with spin lock Content-Language: en-US To: Jeongjun Park , dennis@kernel.org, tj@kernel.org, cl@gentwo.org Cc: akpm@linux-foundation.org, roman.gushchin@linux.dev, rientjes@google.com, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com References: <20250703065600.132221-1-aha310510@gmail.com> 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: <20250703065600.132221-1-aha310510@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspam-User: X-Stat-Signature: s3h6ynf69m9kesansgsmxe68itryaw1e X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E260BA0019 X-HE-Tag: 1752249397-651258 X-HE-Meta: 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 W9ZDF7up 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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 7/3/25 08:56, Jeongjun Park wrote: > pcpu_nr_pages() reads pcpu_nr_populated without any protection, which > causes a data race between read/write. > > However, since this is an intended race, we should add a data_race > annotation instead of add a spin lock. > > Reported-by: syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com > Fixes: 7e8a6304d541 ("/proc/meminfo: add percpu populated pages count") > Suggested-by: Shakeel Butt > Signed-off-by: Jeongjun Park > --- > v2: Change it as suggested by Shakeel Butt > - Link to v1: https://lore.kernel.org/all/20250702082749.141616-1-aha310510@gmail.com/ > --- > mm/percpu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/percpu.c b/mm/percpu.c > index b35494c8ede2..782cc148b39c 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -3355,7 +3355,7 @@ void __init setup_per_cpu_areas(void) > */ > unsigned long pcpu_nr_pages(void) > { > - return pcpu_nr_populated * pcpu_nr_units; > + return data_race(READ_ONCE(pcpu_nr_populated) * pcpu_nr_units); Nit: pcpu_nr_units should be excluded from the scope of data_race() as no race can happen there. > } > > /* > --