From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:42256 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S932998AbcJQSTu (ORCPT <rfc822;linux-fsdevel@vger.kernel.org>);
        Mon, 17 Oct 2016 14:19:50 -0400
From: Jeff Moyer <jmoyer@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: viro@zeniv.linux.org.uk, jack@suse.cz, dmonakhov@openvz.org,
        linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] aio: fix a use after free (and fix freeze protection of aio writes)
References: <1476597082-15317-1-git-send-email-hch@lst.de>
Date: Mon, 17 Oct 2016 14:19:47 -0400
In-Reply-To: <1476597082-15317-1-git-send-email-hch@lst.de> (Christoph
        Hellwig's message of "Sun, 16 Oct 2016 07:51:22 +0200")
Message-ID: <x49twcabzy4.fsf@segfault.boston.devel.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

Hi, Christoph,

Christoph Hellwig <hch@lst.de> writes:

> diff --git a/fs/aio.c b/fs/aio.c
> index 1157e13..bf315cd 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1078,6 +1078,17 @@ static void aio_complete(struct kiocb *kiocb, long res, long res2)
>  	unsigned tail, pos, head;
>  	unsigned long	flags;
>  
> +	if (kiocb->ki_flags & IOCB_WRITE) {
> +		struct file *file = kiocb->ki_filp;
> +
> +		/*
> +		 * Tell lockdep we inherited freeze protection from submission
> +		 * thread.
> +		 */
> +		__sb_writers_acquired(file_inode(file)->i_sb, SB_FREEZE_WRITE);
> +		file_end_write(file);

This ends up being a call to __sb_end_write:

void __sb_end_write(struct super_block *sb, int level)
{
        percpu_up_read(sb->s_writers.rw_sem + level-1);
}

Nothing guarantees that submission and completion happen on the same
CPU.  Is this safe?

-Jeff