linux-ext4 - Re: [PATCH] ext4: fix potential deadlock in ext4_nonda

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Message-ID: <20120921235912.GA27207@thunk.org>
Date:	Fri, 21 Sep 2012 19:59:12 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	stable@...r.kernel.org
Subject: Re: [PATCH] ext4: fix potential deadlock in ext4_nonda_switch()

On Fri, Sep 21, 2012 at 05:12:05PM -0500, Eric Sandeen wrote:
> > -	if (free_blocks < 2 * dirty_blocks)
> > -		writeback_inodes_sb_if_idle(sb, WB_REASON_FS_FREE_SPACE);
> > +	if ((free_blocks < 2 * dirty_blocks) && writeback_in_progress(sb->s_bdi))
> > +		writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
> 
> Looks to me like this inverts the logic.
> 
> We used to write back if idle, now we fire it off if it's already underway.
> 
> Shouldn't it be:
> 
> +	if ((free_blocks < 2 * dirty_blocks) && !writeback_in_progress(sb->s_bdi))
> +		writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);

Oops, nice catch.  Thanks for the review!!

I've added the missing '!' to the patch.

     	   					- Ted
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