linux-ext4 - Re: ext4: Do not dec quota for reserved blocks on error paths v2

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Message-ID: <4BE08215.2050603@redhat.com>
Date:	Tue, 04 May 2010 15:22:45 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
CC:	linux-ext4@...r.kernel.org
Subject: Re: ext4: Do not dec quota for reserved blocks on error paths v2

Dmitry Monakhov wrote:
> If we have failed some where inside ext4_get_blocks() internals we may
> have allocated some new blocks, which was not yet claimed to quota.
> We have to free such blocks, but without touching quota. Quota will
> be updated later on exit from ext4_get_blocks().
> There are two possible ways to understand what we have to skip quota update:
> 1) Caller pass corresponding flag to ext4_free_blocks()
> 2) check that free_blocks() was indirectly called by get_blocks() 
>    (i.e EXT4_I(inode)->i_delalloc_reserved_flag is set)
> Second is simpler, but may result in unpredictable consequences later.
> So i've chosen the first one, because caller must know which blocks it
> is freeing.
> 
> Eric, please take your attention to metadata blocks handling when
> you will work on new versing of  "ext4: don't use quota reservation for
> speculative metadata blocks" patch.
> 
> The bug happens on heavily loaded node, or with 227'th xfstestcase and

hm which test?  227 is xfs-only...

-Eric

> result in incorrect i_blocks (less than expected). So truncation for
> that file result in i_blocks overflow.
> Seems this was the last bug which was easily triggered by 227'th testcase.
> 
> 

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