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[141.239.149.160]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fd6f316d0fsm57840575ad.165.2024.07.22.10.52.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jul 2024 10:52:23 -0700 (PDT) Sender: Tejun Heo Date: Mon, 22 Jul 2024 07:52:22 -1000 From: Tejun Heo To: Boqun Feng Cc: kernel test robot , Suren Baghdasaryan , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , Kent Overstreet , Kees Cook , Alexander Viro , Alex Gaynor , Alice Ryhl , Andreas Hindborg , Benno Lossin , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Christoph Lameter , Dennis Zhou , Gary Guo , Miguel Ojeda , Pasha Tatashin , Peter Zijlstra , Vlastimil Babka , Wedson Almeida Filho , linux-mm@kvack.org, lkmm@lists.linux.dev Subject: Re: [linus:master] [mm] 24e44cc22a: BUG:KCSAN:data-race_in_pcpu_alloc_noprof/pcpu_block_update_hint_alloc Message-ID: References: <202407191651.f24e499d-oliver.sang@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jul 22, 2024 at 10:47:30AM -0700, Boqun Feng wrote: > This looks like a data race because we read pcpu_nr_empty_pop_pages out > of the lock for a best effort checking, @Tejun, maybe you could confirm > on this? That does sound plausible. > - if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW) > + /* > + * Checks pcpu_nr_empty_pop_pages out of the pcpu_lock, data races may > + * occur but this is just a best-effort checking, everything is synced > + * in pcpu_balance_work. > + */ > + if (data_race(pcpu_nr_empty_pop_pages) < PCPU_EMPTY_POP_PAGES_LOW) > pcpu_schedule_balance_work(); Would it be better to use READ/WRITE_ONCE() for the variable? Thanks. -- tejun