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 39CA6320CD5 for ; Fri, 19 Sep 2025 16:15:27 +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=1758298530; cv=none; b=YYtHLXGeyf2juErLnwC1JmkPflHiLVvgs3sebhnE4tBF5qJHYEUe6tX/IkyVMlEvoPZ2uVn4UoYB0uMvDmejAvFIjPjdfuK2ZVGsnU4k+9YxwgG6dhNHZRA3tWwhGkr3LS0hW0ZGUW8YdMn6b2/xYh3mPrwKf45XYQHHeNKcGeg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758298530; c=relaxed/simple; bh=nqdyMymN425TI/5K5SDgLswxxxGJi9ZID2KaXox7sOA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YIw7XlBeY8NYojHWhDWhvbHz4RePrineGwdQiIbtV31Lv57YSaG15K563Jp280S2ui7GTpNqV4ZPPwFEXBWzwCZvabXBb3BZvkNGde9YF9F1+jBo/RP1Dm1iIJizagHMHJ6OHoJQQdtJ1c/GyXPR3kjRNFcWLTU7EKa3EhaOyqc= 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=Ao9vjwtQ; arc=none smtp.client-ip=170.10.133.124 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="Ao9vjwtQ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758298527; 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=tFSWc29Bem6BFsJUg23DgE4402gn/p4b5SW0MKkdQF0=; b=Ao9vjwtQEE/7oz9VwMycwSyidUzcVtV8HHXh6BAQitZmnoYWW8A6yjH2NEiNmsHhLNcGEf rsSrQdFnqOsB84st5zdd+6XfxlyAVwnOJlCxSkdidmb3MRLtp6/lEqp+zG1ky1Fe+FOvjC iboJqGldilDVmrVdRqB0/0n+inqU00s= Received: from mx-prod-mc-03.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-548-9jy5j-zZNyOFIxt8m5gdKw-1; Fri, 19 Sep 2025 12:15:23 -0400 X-MC-Unique: 9jy5j-zZNyOFIxt8m5gdKw-1 X-Mimecast-MFC-AGG-ID: 9jy5j-zZNyOFIxt8m5gdKw_1758298521 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 30F1519560B5; Fri, 19 Sep 2025 16:15:21 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.44.33.8]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id A981519560BB; Fri, 19 Sep 2025 16:15:18 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 19 Sep 2025 18:13:57 +0200 (CEST) Date: Fri, 19 Sep 2025 18:13:54 +0200 From: Oleg Nesterov To: Matt Fleming Cc: Peter Zijlstra , John Stultz , kernel-team , LKML , Chris Arges Subject: Re: Debugging lost task in wait_task_inactive() when delivering signal (6.12) Message-ID: <20250919161353.GB22933@redhat.com> References: <20250919143611.GA22933@redhat.com> Precedence: bulk X-Mailing-List: linux-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 10.30.177.12 Let me repeat that currently I have no idea, so let me ask another stupid question... On 09/19, Matt Fleming wrote: > > I do have some info. The callstack for the lost thread is: > > Call Trace: > > __schedule+0x4fb/0xbf0 > ? srso_return_thunk+0x5/0x5f > schedule+0x27/0xf0 > do_exit+0xdd/0xaa0 > ? __pfx_futex_wake_mark+0x10/0x10 > do_group_exit+0x30/0x80 > get_signal+0x81e/0x860 > ? srso_return_thunk+0x5/0x5f > ? futex_wake+0x177/0x1a0 > arch_do_signal_or_restart+0x2e/0x1f0 > ? srso_return_thunk+0x5/0x5f > ? srso_return_thunk+0x5/0x5f > ? __x64_sys_futex+0x10c/0x1d0 > syscall_exit_to_user_mode+0xa5/0x130 > do_syscall_64+0x57/0x110 > entry_SYSCALL_64_after_hwframe+0x76/0x7e OK, thanks. Nothing "interesting" at first glance. > do_exit+0xdd is here in coredump_task_wait(): > > for (;;) { > set_current_state(TASK_IDLE|TASK_FREEZABLE); > if (!self.task) /* see coredump_finish() */ > break; > schedule(); > } > > i.e. the task calls schedule() and never comes back. Are you sure it never comes back and doesn't loop? > The waiting task > sees p->on_rq=1 for this lost thread Strange... Oleg.