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Sun, 07 Sep 2025 22:23:31 -0700 (PDT) Date: Mon, 8 Sep 2025 13:23:28 +0800 From: Jinchao Wang To: Peter Zijlstra Cc: Andrew Morton , Masami Hiramatsu , "Naveen N . Rao" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-perf-users@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 07/18] mm/ksw: add atomic watch on/off operations Message-ID: References: <20250904002126.1514566-1-wangjinchao600@gmail.com> <20250904002126.1514566-8-wangjinchao600@gmail.com> <20250904064659.GV4067720@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250904064659.GV4067720@noisy.programming.kicks-ass.net> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: F17581C000B X-Stat-Signature: ebhfmazm1muhyo4q36ztsqqetaigr834 X-Rspam-User: X-HE-Tag: 1757309012-757066 X-HE-Meta: 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 USGCYX/m D3lAIptLis0r+VLSybzXfUCHcNn+5/kEbig0adWxGU18MliZwnul74g7fXlyw4VCqVcPP4azwn/9kq2I9tEb6aiE1dSLCo6gkxsJnWl2BSFo/kUyZEvb+15etnp6WJpnXjoGxDDV/skTuzHuXFX1dH2hGTxHk37aRM4c8ks6hWAQrhAT+Si50TUXd4/0dQvtOcTjBc1rzc3LNa6bE2AYlFrLgNsqrtHWyQ/Opxs7+4p565+XJ50qTq2nQBfiTkMns4bExNheBkrJZoQaN2RZ4qTsY6zWEQMrG3v7Ik8D8btm9Q4c8F69ILgDVJkJ/EF+iLVoaNHsMaueNg4cYB2igKkD90o3trKZJtVzb0skj0YpkmUwpvg3nFM6ktol4TkeXdP+9mN9WUs12bU4k3dH27zgkMk6PmXto/KPMbFzGYt40ZfiC8UJwinNLXAAKp6dY6SsOa9+z9nYR43C6/ySL9gJJaMM6qxL9K2mk8XgkkM6tlgRxSX/OACVwG8nS9yp2uOd5 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 Thu, Sep 04, 2025 at 08:46:59AM +0200, Peter Zijlstra wrote: > On Thu, Sep 04, 2025 at 08:21:04AM +0800, Jinchao Wang wrote: > > > +static DEFINE_PER_CPU(call_single_data_t, > > + watch_csd) = CSD_INIT(ksw_watch_on_local_cpu, > > + &watch_info); > > + > > > +int ksw_watch_on(u64 watch_addr, u64 watch_len) > > +{ > > + unsigned long flags; > > + int cpu; > > + > > + if (!watch_addr) { > > + pr_err("KSW: watch with invalid address\n"); > > + return -EINVAL; > > + } > > + > > + spin_lock_irqsave(&watch_lock, flags); > > + > > + /* > > + * check if already watched > > + */ > > + if (watch_info.addr != 0 && // not uninit > > + watch_info.addr != (unsigned long)&watch_holder && // installed > > + watch_addr != (unsigned long)&watch_holder) { //not restore > > + spin_unlock_irqrestore(&watch_lock, flags); > > + return -EBUSY; > > + } > > + > > + watch_info.addr = watch_addr; > > + watch_info.len = watch_len; > > + > > + spin_unlock_irqrestore(&watch_lock, flags); > > + > > + if (watch_addr == (unsigned long)&watch_holder) > > + pr_debug("KSW: watch off starting\n"); > > + else > > + pr_debug("KSW: watch on starting\n"); > > + > > + for_each_online_cpu(cpu) { > > + if (cpu == raw_smp_processor_id()) { > > + ksw_watch_on_local_cpu(&watch_info); > > + } else { > > + call_single_data_t *csd = &per_cpu(watch_csd, cpu); > > + > > + smp_call_function_single_async(cpu, csd); > > + } > > + } > > + > > + return 0; > > +} > > What do you think happens when two ksw_watch_on() instances run > concurrently? > > What happens if a CPU comes online/offline concurrently with > ksw_watch_on()? Thanks for pointing that out. I did not think much about it. I will think more and address it in the next series.