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[XFS] Prevent direct I/O from mapping extents beyond eof

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With the help from some tracing I found that we try to map extents beyond
eof when doing a direct I/O read. It appears that the way to inform the
generic direct I/O path (ie do_direct_IO()) that we have breached eof is
to return an unmapped buffer from xfs_get_blocks_direct(). This will cause
do_direct_IO() to jump to the hole handling code where is will check for
eof and then abort.

This problem was found because a direct I/O read was trying to map beyond
eof and was encountering delayed allocations. The delayed allocations
beyond eof are speculative allocations and they didn't get converted when
the direct I/O flushed the file because there was only enough space in the
current AG to convert and write out the dirty pages within eof. Note that
xfs_iomap_write_allocate() wont necessarily convert all the delayed
allocation passed to it - it will return after allocating the first extent
- so if the delayed allocation extends beyond eof then it will stay that
way.

SGI-PV: 983683

SGI-Modid: xfs-linux-melb:xfs-kern:31929a

Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
This commit is contained in:
Lachlan McIlroy 2008-09-17 16:50:14 +10:00 committed by Lachlan McIlroy
parent 6efdf28177
commit 364f358a73
1 changed files with 4 additions and 0 deletions
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4
fs/xfs/linux-2.6/xfs_aops.c
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@ -1338,6 +1338,10 @@ __xfs_get_blocks(
offset = (xfs_off_t)iblock << inode->i_blkbits;
ASSERT(bh_result->b_size >= (1 << inode->i_blkbits));
size = bh_result->b_size;
if (!create && direct && offset >= i_size_read(inode))
return 0;
error = xfs_iomap(XFS_I(inode), offset, size,
create ? flags : BMAPI_READ, &iomap, &niomap);
if (error)