From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 662F8EEDB for ; Sun, 22 Sep 2024 15:27:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727018873; cv=none; b=NF/xmYaDrB7b9TxhkuSzm6MKPq0bFVaUiPnlIM45K33tFFFcelRUiddnDArG6iLPlInPZRtgxfr6eXmaKmIeltyz4mF984XzjoFvmMt2IF2UqS3Z69I4hkHA9qV8YcVwtduogN5fVS0jfuFeHb2F5xH63ktr40RIMSkbQh+yJlA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727018873; c=relaxed/simple; bh=5KxbnNxFTyBpHlxGL2EYcm6h4Y1pBVBEDHpol40RRP8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OabJuXeZFhLJkw2VSfqefteaS+CW62UxdLAKvwtOLlN4+3nqAWp8mc1eHUetkBCAwdrH0LOnWVeNo3QbcPIZ9zhLMRPEbDOFJKE9UMMy1ypiZz69InT20sm1TlqE9I+45hAHi4PgqWMzrzXjZSLJl2FXb2sii/5o+VUeQa08XJk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=WK4o85T6; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="WK4o85T6" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1727018871; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=WmAfg/OBadr+At/TXJr37YT1rjHHfOwPshCtnw9S2o0=; b=WK4o85T6YCdQs2EeGhpRvOM6A7+BFbRr4aR0SPbzrjUUgYkeekZ+4/zwL0x1tMOGgb8Jpp b+mqi375WD/hfHmHpqeXcZDVJEcSeECV3lTUHUnEWtpNOAUOycbX2ZBPjZUqtgwmL18YH/ n9CgLmTXKkGh7FhzInR8tyN4zJvDMbM= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-452-y9Mf_d30PSGznNZhHB5JkA-1; Sun, 22 Sep 2024 11:27:45 -0400 X-MC-Unique: y9Mf_d30PSGznNZhHB5JkA-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (unknown [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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5089E190ECE8; Sun, 22 Sep 2024 15:27:43 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.14]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 0FCFA19560AB; Sun, 22 Sep 2024 15:27:36 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sun, 22 Sep 2024 17:27:30 +0200 (CEST) Date: Sun, 22 Sep 2024 17:27:23 +0200 From: Oleg Nesterov To: Jiri Olsa Cc: Peter Zijlstra , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf@vger.kernel.org, Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Steven Rostedt , Masami Hiramatsu , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCHv4 02/14] uprobe: Add support for session consumer Message-ID: <20240922152722.GA12833@redhat.com> References: <20240917085024.765883-1-jolsa@kernel.org> <20240917085024.765883-3-jolsa@kernel.org> <20240917120250.GA7752@redhat.com> 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: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Damn, sorry for delay :/ And sorry, still can't understand, see below... On 09/17, Jiri Olsa wrote: > > On Tue, Sep 17, 2024 at 02:03:17PM +0200, Oleg Nesterov wrote: > > > > To me this code should do: > > > > if (!uc->ret_handler || UPROBE_HANDLER_REMOVE || UPROBE_HANDLER_IGNORE) > > continue; > > > > if (!ri) > > ri = alloc_return_instance(); > > > > if (rc == UPROBE_HANDLER_IWANTMYCOOKIE) > > ri = push_consumer(...); > > > > And, > > > > > handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs) > > ... > > > list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node, > > > srcu_read_lock_held(&uprobes_srcu)) { > > > + ric = return_consumer_find(ri, &ric_idx, uc->id); > > > + if (ric && ric->rc == UPROBE_HANDLER_IGNORE) > > > + continue; > > > if (uc->ret_handler) > > > - uc->ret_handler(uc, ri->func, regs); > > > + uc->ret_handler(uc, ri->func, regs, ric ? &ric->cookie : NULL); > > > } > > > > the UPROBE_HANDLER_IGNORE check above and the new ric->rc member should die, > > > > if (!uc->ret_handler) > > continue; > > > > ric = return_consumer_find(...); > > uc->ret_handler(..., ric ? &ric->cookie : NULL); > > > > as we have already discussed, the session ret_handler(data) can simply do > > > > // my ->handler() wasn't called or it didn't return > > // UPROBE_HANDLER_IWANTMYCOOKIE > > if (!data) > > return; > > > > at the start. > > > > Could you explain why this can't work? > > I'll try ;-) it's for the case when consumer does not use UPROBE_HANDLER_IWANTMYCOOKIE > > let's have 2 consumers on single uprobe, consumer-A returning UPROBE_HANDLER_IGNORE > and the consumer-B returning zero, so we want the return uprobe installed, but we > want just consumer-B to be executed > > - so uprobe gets installed and handle_uretprobe_chain goes over all consumers > calling ret_handler callback > > - but we don't know consumer-A needs to be ignored, and it does not > expect cookie so we have no way to find out it needs to be ignored How does this differ from the case when consumer-A returns _REMOVE but another consumer returns 0? But what I really can't understand is and it does not expect cookie so we have no way to find out it needs to be ignored If we change the code as I suggested above, push_consumer() won't be called if consumer-A returns UPROBE_HANDLER_IGNORE. This means that handle_uretprobe_chain() -> return_consumer_find() will return NULL, so handle_uretprobe_chain() won't pass the valid cookie to consumer-A's ret_handler callback, it will pass data => NULL. So, again, why can't consumer-A's ret_handler callback do // my ->handler() wasn't called or it didn't return // UPROBE_HANDLER_IWANTMYCOOKIE if (!data) return; at the start? Why the UPROBE_HANDLER_IGNORE case is more problematic than the UPROBE_HANDLER_REMOVE case? Oleg.