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Wed, 02 Oct 2024 03:25:48 -0400 X-MC-Unique: NKM0WuwcORu4JEE4-zijow-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C59F9195608B; Wed, 2 Oct 2024 07:25:44 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.196]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 68A7A19560A2; Wed, 2 Oct 2024 07:25:38 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 2 Oct 2024 09:25:30 +0200 (CEST) Date: Wed, 2 Oct 2024 09:25:23 +0200 From: Oleg Nesterov To: Andrii Nakryiko Cc: linux-trace-kernel@vger.kernel.org, peterz@infradead.org, 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, linux-mm@kvack.org, mjguzik@gmail.com, brauner@kernel.org, jannh@google.com, mhocko@kernel.org, vbabka@suse.cz, mingo@kernel.org Subject: Re: [PATCH v2 tip/perf/core 5/5] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution Message-ID: <20241002072522.GB27552@redhat.com> References: <20241001225207.2215639-1-andrii@kernel.org> <20241001225207.2215639-6-andrii@kernel.org> Precedence: bulk X-Mailing-List: bpf@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: <20241001225207.2215639-6-andrii@kernel.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On 10/01, Andrii Nakryiko wrote: > > +static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr) > +{ > + struct mm_struct *mm = current->mm; > + struct uprobe *uprobe = NULL; > + struct vm_area_struct *vma; > + struct file *vm_file; > + loff_t offset; > + long seq; > + > + guard(rcu)(); > + > + if (!mmap_lock_speculation_start(mm, &seq)) > + return NULL; > + > + vma = vma_lookup(mm, bp_vaddr); > + if (!vma) > + return NULL; > + > + /* vm_file memory can be reused for another instance of struct file, > + * 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; > + > + offset = (loff_t)(vma->vm_pgoff << PAGE_SHIFT) + (bp_vaddr - vma->vm_start); LGTM. But perhaps vma->vm_pgoff and vma->vm_start need READ_ONCE() as well, if nothing else to shut up KCSAN if this code races with, say, __split_vma() ? > + uprobe = find_uprobe_rcu(vm_file->f_inode, offset); OK, I guess vm_file->f_inode is fine without READ_ONCE... Oleg.