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 E455C18E745 for ; Thu, 8 Aug 2024 14:29:29 +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=1723127371; cv=none; b=fQ67fiYIET3tqe1HivSxUvehWM0s8cLliD5chT+UfLRI0BxLBqlxrXisxAfw5juK6CJyagVcH9hLQMb5P1TUrzcXE/zS8dm39Bdzs3gXrTch2TAziRLAitOTfxn3uST+5IAzuxF13PtCxkGmoYu6rj8596uRaC7lJT7WYB/q0Q4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723127371; c=relaxed/simple; bh=gDND6qNLPtj9Cvnqepa/26hTXzqHsUw/LUV9SpFzEO8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=RSBWF08rmZvaH50vBx1qqRzzx1FgUNvJa5KsgJQUMNbD0w3Nvn87Oyp2mMb0XTit9LA1iiOHubce+yADUaGCwaVFzudzTL+mAY1KNJiwOKOEi2FXB52f7jPe0mInaoNx4OmFAsfz+65L6UjEJh66S+3csNF5G4ktqboSu8PEc+c= 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=PEUC4seg; 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="PEUC4seg" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1723127368; 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=gDND6qNLPtj9Cvnqepa/26hTXzqHsUw/LUV9SpFzEO8=; b=PEUC4segrJEsUCo0KXlaygV7EgVTU9zaJlueDBPFzJuq6FQBo/0hYNxxKqwtGhkdLFEKmv Y5VPtEUnZVIMDquSxFYj0xWm9nq0eYbPYonUowbCG5yXVHomH18WiN41bBwWAq7sEQQ8Gd s0xBXPXWzqgK7ssoQXmjpX7y2yqAwgc= Received: from mx-prod-mc-05.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-314-hgslZID_PW2LeFYh0ix_Vw-1; Thu, 08 Aug 2024 10:29:25 -0400 X-MC-Unique: hgslZID_PW2LeFYh0ix_Vw-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 608F119560A3; Thu, 8 Aug 2024 14:29:23 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.225.189]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 3F7AF19560A3; Thu, 8 Aug 2024 14:29:18 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 8 Aug 2024 16:29:21 +0200 (CEST) Date: Thu, 8 Aug 2024 16:29:16 +0200 From: Oleg Nesterov To: Andrii Nakryiko Cc: Andrii Nakryiko , 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 Subject: Re: [PATCH 7/8] uprobes: perform lockless SRCU-protected uprobes_tree lookup Message-ID: <20240808142916.GF8020@redhat.com> References: <20240731214256.3588718-1-andrii@kernel.org> <20240731214256.3588718-8-andrii@kernel.org> Precedence: bulk X-Mailing-List: linux-trace-kernel@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 10.30.177.40 On 08/07, Andrii Nakryiko wrote: > > So, any ideas how we can end up with "corrupted" root on lockless > lookup with rb_find_rcu()? I certainly can't help ;) I know ABSOLUTELY NOTHING about rb or any other tree. But, > This seems to be the very first lockless > RB-tree lookup use case in the tree, Well, latch_tree_find() is supposed to be rcu-safe afaics, and __lt_erase() is just rb_erase(). So it is not the 1st use case. See also the "Notes on lockless lookups" comment in lib/rbtree.c. So it seems that rb_erase() is supposed to be rcu-safe. However it uses __rb_change_child(), not __rb_change_child_rcu(). Not that I think this can explain the problem, and on x86 __smp_store_release() is just WRITE_ONCE, but looks confusing... Oleg.