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Thu, 01 Sep 2022 18:59:24 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 8F5993002C7; Thu, 1 Sep 2022 20:59:20 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 729172B8B840F; Thu, 1 Sep 2022 20:59:20 +0200 (CEST) Date: Thu, 1 Sep 2022 20:59:20 +0200 From: Peter Zijlstra To: Kent Overstreet Cc: Suren Baghdasaryan , akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, roman.gushchin@linux.dev, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, void@manifault.com, juri.lelli@redhat.com, ldufour@linux.ibm.com, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, changbin.du@intel.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, shakeelb@google.com, songmuchun@bytedance.com, arnd@arndb.de, jbaron@akamai.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, kernel-team@android.com, linux-mm@kvack.org, iommu@lists.linux.dev, kasan-dev@googlegroups.com, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, xen-devel@lists.xenproject.org, linux-bcache@vger.kernel.org, linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 03/30] Lazy percpu counters Message-ID: References: <20220830214919.53220-1-surenb@google.com> <20220830214919.53220-4-surenb@google.com> <20220901143219.n7jg7cbp47agqnwn@moria.home.lan> MIME-Version: 1.0 Content-Type: text/plain; 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t=1662058793; a=rsa-sha256; cv=none; b=M3cCoFbJ4P33TluZiHW8WNaQpaG8DtuXoBnTSX23312ma7qOpNT9bL/nqF0hEGMSA4qSh6 ronofxVgneegu8oRtB0YnSgunLdGODtcssv/IGi3hzZ3+y1ZLO8Z0ZwI5K7rfCe3V8grwx aDPwG2iYOiixjgDHmmnNiGQLxEHO1jQ= Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=Cn40tdhd; dmarc=none; spf=none (imf04.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org X-Rspamd-Queue-Id: 6D6424004E X-Stat-Signature: xei5ffb6tr1tdythdrtircme9tybam6a X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1662058793-948741 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: On Thu, Sep 01, 2022 at 10:32:19AM -0400, Kent Overstreet wrote: > On Thu, Sep 01, 2022 at 08:51:31AM +0200, Peter Zijlstra wrote: > > On Tue, Aug 30, 2022 at 02:48:52PM -0700, Suren Baghdasaryan wrote: > > > +static void lazy_percpu_counter_switch_to_pcpu(struct raw_lazy_percpu_counter *c) > > > +{ > > > + u64 __percpu *pcpu_v = alloc_percpu_gfp(u64, GFP_ATOMIC|__GFP_NOWARN); > > > > Realize that this is incorrect when used under a raw_spinlock_t. > > Can you elaborate? required lock order: raw_spinlock_t < spinlock_t < mutex allocators lives at spinlock_t. Also see CONFIG_PROVE_RAW_LOCK_NESTING and there might be a document mentioning all this somewhere. Additionally, this (obviously) also isn't NMI safe.