From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BE3C813777F; Wed, 10 Jul 2024 09:40:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720604421; cv=none; b=fCGdOqmB5M0NOk2NvTWbWEXeOKUeBhMcvgK2nOWgiYPLdKHe/WsFoK5IszbfMGxICuBVC+dFIbhjNLSt4WWAgJ3QTMYj33XNI2XS2AMr4r8syt11xkiDA2U/P8CDxCmyrS5XUBfb268uTyxrc/A8L6LqJl8UfEQZf7RLtrs/epw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720604421; c=relaxed/simple; bh=61L9rkQ9dqZ3QSieSK9JvifiNh4ZOARWpXT+HEj3SOU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ad1cspxVyq93R3TzNHulfaq2kgbDswP8e8oiJm7HoSok1uuJU5vQc7xSMyef/uXeD2xcy5PAjjgROyZPPOqSS3Msh/8AciCuvrajHBxQouk+Ou2CEuWCZzwvtvdW3sV/qp//ZGz8upm2qisHo85TrgFMGHkwQYTwdhJEAWBLtH8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=JTZigf1f; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="JTZigf1f" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=eEGyTTl/W/CCsANw8ThDof7pn/KbfM1qr9ZJYXfiiyo=; b=JTZigf1fyby+hNl6845U/wiln+ C/g6HrgrMqpYjR6qvFIwN2htygfrc5+eq/a0CeC3g1G6ghz0SCo5/E2PW0dhaIdfTvOs45McNSSBz r0U6WMv+7pTWS8COtR5UIIUQOde2nv4wNm+k6G4SGOwTTmjIUH5zsGt7kt8O+10r0aJ9IlX0fl5MO UjUvkW0ISFVe4tlQLZCpYNXGlqt6NA1FCh67UqDxYM+/EigP+9PcKDMk3aasuXI4uKZKklTJfC+SF 79oFIsgctpyfpv3H1qNQawvpZSXlhm95al2eRWD9h4xz1eXn/wHwncrBBLMd6HpnYWGofehaSHYym yQL86TyA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.97.1 #2 (Red Hat Linux)) id 1sRTo5-00000000t0L-44IM; Wed, 10 Jul 2024 09:40:14 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 99542300694; Wed, 10 Jul 2024 11:40:13 +0200 (CEST) Date: Wed, 10 Jul 2024 11:40:13 +0200 From: Peter Zijlstra To: Matthew Wilcox Cc: "Paul E. McKenney" , Andrii Nakryiko , Masami Hiramatsu , mingo@kernel.org, andrii@kernel.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, oleg@redhat.com, jolsa@kernel.org, clm@meta.com, bpf Subject: Re: [PATCH 00/10] perf/uprobe: Optimize uprobes Message-ID: <20240710094013.GF28838@noisy.programming.kicks-ass.net> References: <20240708091241.544262971@infradead.org> <20240709075651.122204f1358f9f78d1e64b62@kernel.org> <20240709090153.GF27299@noisy.programming.kicks-ass.net> <91d37ad3-137b-4feb-8154-4deaa4b11dc3@paulmck-laptop> <20240709142943.GL27299@noisy.programming.kicks-ass.net> <20240710091631.GT27299@noisy.programming.kicks-ass.net> 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: <20240710091631.GT27299@noisy.programming.kicks-ass.net> On Wed, Jul 10, 2024 at 11:16:31AM +0200, Peter Zijlstra wrote: > If it were an actual sequence count, I could make it work, but sadly, > not. Also, vma_end_write() seems to be missing :-( If anything it could > be used to lockdep annotate the thing. > > Mooo.. I need to stare more at this to see if perhaps it can be made to > work, but so far, no joy :/ See, this is what I want, except I can't close the race against VMA modification because of that crazy locking scheme :/ --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -2146,11 +2146,58 @@ static int is_trap_at_addr(struct mm_str return is_trap_insn(&opcode); } -static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp) +#ifndef CONFIG_PER_VMA_LOCK +static struct uprobe *__find_active_uprobe(unsigned long bp_vaddr) +{ + return NULL; +} +#else +static struct uprobe *__find_active_uprobe(unsigned long bp_vaddr) { struct mm_struct *mm = current->mm; struct uprobe *uprobe = NULL; struct vm_area_struct *vma; + MA_STATE(mas, &mm->mm_mt, bp_vaddr, bp_vaddr); + + guard(rcu)(); + +again: + vma = mas_walk(&mas); + if (!vma) + return NULL; + + /* vma_write_start() -- in progress */ + if (READ_ONCE(vma->vm_lock_seq) == READ_ONCE(vma->vm_mm->mm_lock_seq)) + return NULL; + + /* + * Completely broken, because of the crazy vma locking scheme you + * cannot avoid the per-vma rwlock and doing so means you're racy + * against modifications. + * + * A simple actual seqcount would'be been cheaper and more usefull. + */ + + if (!valid_vma(vma, false)) + return NULL; + + struct inode = file_inode(vma->vm_file); + loff_t offset = vaddr_to_offset(vma, bp_vaddr); + + // XXX: if (vma_seq_retry(...)) goto again; + + return find_uprobe(inode, offset); +} +#endif + +static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp) +{ + struct uprobe *uprobe = __find_active_uprobe(bp_vaddr) + struct mm_struct *mm = current->mm; + struct vm_area_struct *vma; + + if (uprobe) + return uprobe; mmap_read_lock(mm); vma = vma_lookup(mm, bp_vaddr);