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Btrfs: deal with duplciates during extent_map insertion in btrfs_get_extent
When dealing with inline extents, btrfs_get_extent will incorrectly try to insert a duplicate extent_map. The dup hits -EEXIST from add_extent_map, but then we try to merge with the existing one and end up trying to insert a zero length extent_map. This actually works most of the time, except when there are extent maps past the end of the inline extent. rocksdb will trigger this sometimes because it preallocates an extent and then truncates down. Josef made a script to trigger with xfs_io: #!/bin/bash xfs_io -f -c "pwrite 0 1000" inline xfs_io -c "falloc -k 4k 1M" inline xfs_io -c "pread 0 1000" -c "fadvise -d 0 1000" -c "pread 0 1000" inline xfs_io -c "fadvise -d 0 1000" inline cat inline You'll get EIOs trying to read inline after this because add_extent_map is returning EEXIST Signed-off-by: Chris Mason <clm@fb.com>
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@ -6979,7 +6979,18 @@ struct extent_map *btrfs_get_extent(struct inode *inode, struct page *page,
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* existing will always be non-NULL, since there must be
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* existing will always be non-NULL, since there must be
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* extent causing the -EEXIST.
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* extent causing the -EEXIST.
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*/
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*/
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if (start >= extent_map_end(existing) ||
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if (existing->start == em->start &&
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extent_map_end(existing) == extent_map_end(em) &&
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em->block_start == existing->block_start) {
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/*
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* these two extents are the same, it happens
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* with inlines especially
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*/
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free_extent_map(em);
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em = existing;
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err = 0;
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} else if (start >= extent_map_end(existing) ||
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start <= existing->start) {
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start <= existing->start) {
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/*
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/*
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* The existing extent map is the one nearest to
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* The existing extent map is the one nearest to
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