linux-ext4 - punch-hole should go beyond i

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Message-ID: <alpine.LSU.2.00.1201111639240.1833@eggly.anvils>
Date:	Wed, 11 Jan 2012 17:02:12 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Allison Henderson <achender@...ux.vnet.ibm.com>
cc:	linux-ext4@...r.kernel.org
Subject: punch-hole should go beyond i_size

Hi Allison,

In thinking about fallocate() on tmpfs, I cross-check with ext4
and find this bug in its implementation of FALLOC_FL_PUNCH_HOLE:

rm -f temp
fallocate    -l 4096 temp
du temp				# shows 4, right
fallocate -p -l 4096 temp
du temp				# shows 0, right
rm -f temp
fallocate -n -l 4096 temp
du temp				# shows 4, right
fallocate -p -l 4096 temp
du temp				# shows 4, wrong
rm temp

ext4_ext_punch_hole() contains /* No need to punch hole beyond i_size */
early return, and trimming to i_size below, but forgets that the other
variety of fallocate(), with FALLOC_FL_KEEP_SIZE set, may have allocated
blocks beyond i_size.  They can be removed with ftruncate(), but it is
unexpected for fallocate() not to undo its own work, and xfs does so.

Hugh
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