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 7612056473 for ; Sat, 27 Jan 2024 16:33:02 +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=1706373184; cv=none; b=eDDe7WcsoQQKQRrIan0JzHynVvAcq+kbec3X990paWaR1IeQYjyzCIDp6Rpg1sLJh6RznIyFEiiatXJGZkjT4uzpFtnLUKwYWV/Kknf33pG6OD69fNsbAiNly8436k0YH/Iz+e5UG4S9Y++9kIT30V2kJgcO0S4mS1lt3RRTe4g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706373184; c=relaxed/simple; bh=kCA9TsgWAj9jn5vlEBGgkwF7celX9k9TNJISTn56xmI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ocaThquUR3ty1nOCyhU8hiDYQcER2C7/JpV2YErteVLFZj4OYoOX3PDNG06zF2XPgrVWBuNSz+mpwFrQrJcbIhlDBqLLImggszvOZz3jAPtZqn89R9BAadqAvsQnn1X3n0J+/iehh8xDO1iU6YbHSQy8q63SN9vS0dt8+piOkLc= 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=DdFS4rez; 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="DdFS4rez" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1706373181; 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=kCA9TsgWAj9jn5vlEBGgkwF7celX9k9TNJISTn56xmI=; b=DdFS4rez6b1FpM7VDRDPe9I/S/64LdhV4mdmdQICFscCFQJ0SeQh01D3U/JzhWycxb8DyO zhZBASOAV5/AXicUiFd1palTkxlf1cBHmSKhN0Lz5g8dQg+xUu4amKudacOqHd4APNJR6p 5AaNaLIxfe/i0A/Sh+saF+egaovdiaw= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-614-Fc0-O_u7Mjaip4MGg-JMYQ-1; Sat, 27 Jan 2024 11:32:55 -0500 X-MC-Unique: Fc0-O_u7Mjaip4MGg-JMYQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 65637835381; Sat, 27 Jan 2024 16:32:55 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.4]) by smtp.corp.redhat.com (Postfix) with SMTP id D52E42166B32; Sat, 27 Jan 2024 16:32:53 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sat, 27 Jan 2024 17:31:41 +0100 (CET) Date: Sat, 27 Jan 2024 17:31:39 +0100 From: Oleg Nesterov To: Tycho Andersen Cc: Christian Brauner , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Tycho Andersen , "Eric W. Biederman" Subject: Re: [PATCH v3 1/3] pidfd: allow pidfd_open() on non-thread-group leaders Message-ID: <20240127163117.GB13787@redhat.com> References: <20240123153452.170866-1-tycho@tycho.pizza> <20240123153452.170866-2-tycho@tycho.pizza> <20240123195608.GB9978@redhat.com> <20240125140830.GA5513@redhat.com> <20240127105410.GA13787@redhat.com> Precedence: bulk X-Mailing-List: linux-api@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 3.4.1 on 10.11.54.6 On 01/27, Tycho Andersen wrote: > > It seems like (and the current pidfd_test enforces for some cases) Which pidfd_test ? > we > want exactly one notification for a task dying. This can't be right. EVERY user of poll_wait() or wait_event/etc must handle/tolerate the false wakeups. > I don't understand > how we guarantee this now, with all of these calls. I don't understand why do we need or even want to guarantee this. The extra wakeup must be always fine correctness-wise. Sure, it would be nice to avoid the unnecessary wakeups, and perhaps we can change wake_up_all() to pass a key to, say, only wake_up the PIDFD_THREAD waiters from exit_notify(). But certainly this is outside the scope of PIDFD_THREAD change we discuss. The changes in do_notify_parent() (I have already sent the patch) and in exit_notify() (proposed in my previous email) just ensure that, with the minimal changes, we avoid 2 do_notify_pidfd's from the same exit_notify() path. > > exit_notify() is called after exit_files(). pidfd_getfd() returns > > ESRCH if the exiting thread completes release_task(), otherwise it > > returns EBADF because ->files == NULL. This too doesn't really > > depend on PIDFD_THREAD. > > Yup, understood. It just seems like an inconsistency we might want to > fix. Not sure this worth "fixing"... Oleg.