From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f54.google.com (mail-pb0-f54.google.com [209.85.160.54]) by kanga.kvack.org (Postfix) with ESMTP id A3DC96B0031 for ; Mon, 14 Oct 2013 05:47:40 -0400 (EDT) Received: by mail-pb0-f54.google.com with SMTP id ro12so7115851pbb.27 for ; Mon, 14 Oct 2013 02:47:40 -0700 (PDT) Received: from eucpsbgm2.samsung.com (unknown [203.254.199.245]) by mailout4.w1.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0MUN00CM5KITFN30@mailout4.w1.samsung.com> for linux-mm@kvack.org; Mon, 14 Oct 2013 10:47:36 +0100 (BST) Message-id: <1381744054.24685.35.camel@AMDC1943> Subject: Re: [PATCH] swap: fix set_blocksize race during swapon/swapoff From: Krzysztof Kozlowski Date: Mon, 14 Oct 2013 11:47:34 +0200 In-reply-to: <20131011120226.1f4bb32569f370b57b841e79@linux-foundation.org> References: <1381485262-16792-1-git-send-email-k.kozlowski@samsung.com> <20131011120226.1f4bb32569f370b57b841e79@linux-foundation.org> Content-type: text/plain; charset=UTF-8 Content-transfer-encoding: 7bit MIME-version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Weijie Yang , Bob Liu , Konrad Rzeszutek Wilk , Shaohua Li , Minchan Kim , Hugh Dickins On Fri, 2013-10-11 at 12:02 -0700, Andrew Morton wrote: > (cc Hugh) > > On Fri, 11 Oct 2013 11:54:22 +0200 Krzysztof Kozlowski wrote: > > > Swapoff used old_block_size from swap_info which could be overwritten by > > concurrent swapon. > > > > Reported-by: Weijie Yang > > Signed-off-by: Krzysztof Kozlowski > > --- > > mm/swapfile.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index 3963fc2..de7c904 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -1824,6 +1824,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) > > struct filename *pathname; > > int i, type, prev; > > int err; > > + unsigned int old_block_size; > > > > if (!capable(CAP_SYS_ADMIN)) > > return -EPERM; > > @@ -1914,6 +1915,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) > > } > > > > swap_file = p->swap_file; > > + old_block_size = p->old_block_size; > > p->swap_file = NULL; > > p->max = 0; > > swap_map = p->swap_map; > > @@ -1938,7 +1940,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) > > inode = mapping->host; > > if (S_ISBLK(inode->i_mode)) { > > struct block_device *bdev = I_BDEV(inode); > > - set_blocksize(bdev, p->old_block_size); > > + set_blocksize(bdev, old_block_size); > > blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); > > } else { > > mutex_lock(&inode->i_mutex); > > I find it worrying that a swapon can run concurrently with any of this > swapoff code. It just seem to be asking for trouble and the code > really isn't set up for this and races here will be poorly tested for > > I'm wondering if we should just extend swapon_mutex a lot and eliminate > the concurrency? It seems there are even more races here between swapoff & swapon (and swapon with swapon). Simple script: for i in `seq 1000` do swapoff -a & swapon -a & done causes frequent switches of block size of devices (jumping from 512 to 4096). Best regards, Krzysztof -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org