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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1t3hp8-00000008Xve-2Uon; Wed, 23 Oct 2024 20:19:21 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id EFC4830073F; Wed, 23 Oct 2024 22:19:17 +0200 (CEST) Date: Wed, 23 Oct 2024 22:19:17 +0200 From: Peter Zijlstra To: Andrii Nakryiko Cc: Andrii Nakryiko , linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, akpm@linux-foundation.org, mjguzik@gmail.com, brauner@kernel.org, jannh@google.com, mhocko@kernel.org, vbabka@suse.cz, shakeel.butt@linux.dev, hannes@cmpxchg.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com Subject: Re: [PATCH v3 tip/perf/core 4/4] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution Message-ID: <20241023201917.GG11151@noisy.programming.kicks-ass.net> References: <20241010205644.3831427-1-andrii@kernel.org> <20241010205644.3831427-5-andrii@kernel.org> <20241023192236.GB11151@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: DE54B1A0021 X-Stat-Signature: x1hqrpahkaqxud5jsxuy415rbpco1i7p X-HE-Tag: 1729714752-943858 X-HE-Meta: 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 sPZEWyO+ ZfZ8WkNg5jDVTljYpQrE7DJb0fIGVDmKEZNGE0ttvnlgrBsFAlpxMI5J//CgIqVGNw8Cnx1aYNSHFMCQguuQW9qNp56BahcqHs2orD7/14mSOnrf5omB4ofIbBUWUp+llZlS0cso+7/5t5wq8kTAIbgz9QqaKvoIKobgUetsPMly8xf4Ge0d7mCh84JWxeA/si5jW2aodNsDzmzpnyM1g5sDhEFflICF5JRJLMrug07uTlktkBl9foEA56QLMCpQKQB6GjXwykNymgjU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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 Wed, Oct 23, 2024 at 01:02:53PM -0700, Andrii Nakryiko wrote: > > > + * but can't be freed from under us, so it's safe to read fields from > > > + * it, even if the values are some garbage values; ultimately > > > + * find_uprobe_rcu() + mmap_lock_speculation_end() check will ensure > > > + * that whatever we speculatively found is correct > > > + */ > > > + vm_file = READ_ONCE(vma->vm_file); > > > + if (!vm_file) > > > + return NULL; > > > + > > > + vm_pgoff = data_race(vma->vm_pgoff); > > > + vm_start = data_race(vma->vm_start); > > > + vm_inode = data_race(vm_file->f_inode); > > > > So... seqcount has kcsan annotations other than data_race(). I suppose > > this works, but it all feels like a bad copy with random changes. > > I'm not sure what this means... Do I need to change anything? Drop > data_race()? Use READ_ONCE()? Do nothing? Keep for now. I've ranted at 1/n a bit, but unless the response is: yeah, obviously this should be seqcount (unlikely) this is something that can be fixed later (*sigh* always later... this todo list is a problem).