linux-kernel - Re: [PATCH 5/5] writeback: check skipped pages on WB_SYNC

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20101109144728.d405453d.akpm@linux-foundation.org>
Date:	Tue, 9 Nov 2010 14:47:28 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
	Christoph Hellwig <hch@....de>,
	Jan Engelhardt <jengelh@...ozas.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] writeback: check skipped pages on WB_SYNC_ALL

On Tue, 09 Nov 2010 07:09:21 +0800
Wu Fengguang <fengguang.wu@...el.com> wrote:

> In WB_SYNC_ALL mode, filesystems are not expected to skip dirty pages on
> temporal lock contentions or non fatal errors, otherwise sync() will
> return without actually syncing the skipped pages. Add a check to
> catch possible redirty_page_for_writepage() callers that violate this
> expectation.
> 
> I'd recommend to keep this check in -mm tree for some time and fixup the
> possible warnings before pushing it to upstream.
> 
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
>  fs/fs-writeback.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> --- linux-next.orig/fs/fs-writeback.c	2010-11-07 22:01:06.000000000 +0800
> +++ linux-next/fs/fs-writeback.c	2010-11-07 22:01:15.000000000 +0800
> @@ -527,6 +527,7 @@ static int writeback_sb_inodes(struct su
>  			 * buffers.  Skip this inode for now.
>  			 */
>  			redirty_tail(inode);
> +			WARN_ON_ONCE(wbc->sync_mode == WB_SYNC_ALL);
>  		}
>  		spin_unlock(&inode_lock);
>  		iput(inode);

This is quite kernel-developer-unfriendly.

Suppose the warning triggers.  Now some poor schmuck looks at the
warning and doesn't have a *clue* why it was added.  He has to run off
and grovel through git trees finding changelogs, which is a real pain
if the code has been trivially altered since it was first added.

As a general rule, a kernel developer should be able to look at a
warning callsite and then work out why the warning was emitted!


IOW, you owe us a code comment, please.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/