From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 8442523875A for ; Wed, 2 Apr 2025 14:13:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743603213; cv=none; b=awBS9N9a2z6JIclAkyMXpE48xKokl+C6R6NO7fFfgp5mCDKQgOUjfUduf9WGdMwGP7a6om3zX3hQyf6BivZ/ae49UPqUdNvQXcfmE3a4PDymR65Y1BNtarXPoz9ZzkQk4fDPZADVPxEYWF21k34Yxy88B9e0vhofNTudkzI608w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743603213; c=relaxed/simple; bh=Q4UCbuv+br4mds4Lq3J19ZZ2gTK1+FghExkwwrYhO54=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=RE3c+zKFYUrT1Idpdi7wzndUEN3v34Zs/Ht6xiV1DlW7nSy7X5SysvhmQ6W/h3/p6smMFJvc9y9UoGzs9qXalc3vCSYLdnDq1Wj1xK9P025EsRhO3vJ4bub1QZA15Y4Ptb0i2edBqA+Y5v73/jOZidvP0K9O3eim6lCq+dbDlgs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine 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=R5u31CVq; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine 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="R5u31CVq" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1743603210; 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=Q4UCbuv+br4mds4Lq3J19ZZ2gTK1+FghExkwwrYhO54=; b=R5u31CVqKQzCppellpVvO4a3Thixmm7S6bD55IsvG0R9DxpdEgTIaqIqAcCHwpaN2lIoeq tGmquf5XyVIqtyHGNqnnus+qZeKTYrHuK0jTEeJYIlni/oVH0+n1ZOZj0rc1thI9u3L9hZ 31h3LqdVis19d+5zWYbQeHGOUkNjV6I= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-211-LIwzc2z9OkypURv4CrwrrA-1; Wed, 02 Apr 2025 10:13:27 -0400 X-MC-Unique: LIwzc2z9OkypURv4CrwrrA-1 X-Mimecast-MFC-AGG-ID: LIwzc2z9OkypURv4CrwrrA_1743603205 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 942C1180AB19; Wed, 2 Apr 2025 14:13:25 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.44.34.147]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 33786180A803; Wed, 2 Apr 2025 14:13:21 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 2 Apr 2025 16:12:50 +0200 (CEST) Date: Wed, 2 Apr 2025 16:12:46 +0200 From: Oleg Nesterov To: Sebastian Sewior Cc: Andrii Nakryiko , Steven Rostedt , Peter Ziljstra , Alexei Starovoitov , Andrii Nakryiko , bpf , Jiri Olsa , Masami Hiramatsu Subject: Re: uprobe splat in PREEMP_RT Message-ID: <20250402141245.GK22091@redhat.com> References: <20250401172225.06b01b22@gandalf.local.home> <20250402103326.GD22091@redhat.com> <20250402105746.FMPvRBwL@linutronix.de> <20250402112308.GF22091@redhat.com> <20250402121315.UdZVK1JE@linutronix.de> <20250402121850.GI22091@redhat.com> <20250402122447.B3XIrQnG@linutronix.de> 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: <20250402122447.B3XIrQnG@linutronix.de> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On 04/02, Sebastian Sewior wrote: > > On 2025-04-02 14:18:51 [+0200], Oleg Nesterov wrote: > > On 04/02, Sebastian Sewior wrote: > > I need to tell mutt to replace my name in case it is misspelled. Hmm... have I misspelled your name somewhere? If yes - my apologies. > > > The preempted ri_timer() could stall a read_seqcount_begin(). > > > > Again, nobody use read_seqcount_begin(utask->ri_seqcount). > > > > free_ret_instance() uses raw_seqcount_try_begin(utask->ri_seqcount), > > which, since ri_seqcount is seqcount_t, is just smp_load_acquire(). > > This can't stall. > > Yes. This would work for here just to skip the check because of all > details that are hard to express. Therefore I suggested to use > raw_write_seqcount_begin() instead of write_seqcount_begin() in > 20250402122158.j_8VoHQ-@linutronix.de. Would that work? If this can work, then let me repeat: why can't we turn ->ri_seqcount into a boolean? That was my question. I don't understand the purpose of "seqcount_t ri_seqcount" regardless of the reported problem. This "WARNING: CPU: 0 PID: 16 at include/linux/seqlock.h:221" is another issue. Again, I must have missed something. Oleg.