From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (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 9651584A5B; Thu, 5 Dec 2024 14:18:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733408336; cv=none; b=sl5myWjSNrvAes4WLjrmn0m8IobNGhr2uFjBVYLFUaWmIIVfjaokA4wmtIEPhU2aPpN7BEWBjxlr8f6zpEBspS0FOV7aaG7qXOOs503vQKKktc05BNQZOctEtHed/Rc82HGgxtMl/gEZ/ugn7DEHNvnk89bmWxvUyXZ/IQE1QcE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733408336; c=relaxed/simple; bh=a2B2Dj4fWLN39XL0GnueLCtei8vr48XbIOnRCnLUHiM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Vw4pbaX/XwnKI3A2vYyK4GoJ8fHLW0RuW2gN3tmnww3ZrtujrV+os+tvhJZPrShff9bnSgBrpNoLWgtbcKMqr/g+e18CrJvmS50QTLGU0uw40uR0wQpJvWGstmSk11n74mmKgRercaAqZ53x4EowyGRdpSLw2KdhivqrOWSBv3E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=hNvUabuA; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="hNvUabuA" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=1FnD7vYDvYGjn7VoepL9sooEb2SIm6Bnyb1TmQSbVic=; b=hNvUabuAbI1r+JzxLwFqEocFXs qPBoCxu++XVo2iuuGcS/xsDVrO0//7vSXAzGFHrqNcNGntH4Tg+RRgBIG2tS4jIlwpMiAs3uH/V5H sx7Y2lNy8hybvTlaoA1A2HUs96MeCqvmmQh65+1h5SrrItgJEIukLE8IiWA3/lLcerwdaidSRVtVy S29A5xVLzp829hsRb3Zp8Jdt8YJEuRYannbKNePBhK4INt8xqd6KueJL9ik4m9H9iZ17EoTIRgfVB IDOk0JeAJ7foEK4h/M8ghvxwSKWsTAUddfrHqye9tR+N8NCgNsCyjuI0wRllfoqYfcpW0RCjURRIn 9PWZrENg==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.98 #2 (Red Hat Linux)) id 1tJCgs-000000058ni-0FBh; Thu, 05 Dec 2024 14:18:50 +0000 Date: Thu, 5 Dec 2024 14:18:50 +0000 From: Al Viro To: Mateusz Guzik Cc: paulmck@kernel.org, brauner@kernel.org, jack@suse.cz, linux-fsdevel@vger.kernel.org, torvalds@linux-foundation.org, edumazet@google.com, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] fs: elide the smp_rmb fence in fd_install() Message-ID: <20241205141850.GS3387508@ZenIV> References: <20241205120332.1578562-1-mjguzik@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@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: <20241205120332.1578562-1-mjguzik@gmail.com> Sender: Al Viro On Thu, Dec 05, 2024 at 01:03:32PM +0100, Mateusz Guzik wrote: > void fd_install(unsigned int fd, struct file *file) > { > - struct files_struct *files = current->files; > + struct files_struct *files; > struct fdtable *fdt; > > if (WARN_ON_ONCE(unlikely(file->f_mode & FMODE_BACKING))) > return; > > + /* > + * Synchronized with expand_fdtable(), see that routine for an > + * explanation. > + */ > rcu_read_lock_sched(); > + files = READ_ONCE(current->files); What are you trying to do with that READ_ONCE()? current->files itself is *not* changed by any of that code; current->files->fdtab is.