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Btrfs: Fix bookend extent race v2

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When dropping middle part of an extent, btrfs_drop_extents truncates
the extent at first, then inserts a bookend extent.

Since truncation and insertion can't be done atomically, there is a small
period that the bookend extent isn't in the tree. This causes problem for
functions that search the tree for file extent item. The way to fix this is
lock the range of the bookend extent before truncation.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
This commit is contained in:
Yan Zheng
2008-10-30 14:19:50 -04:00
committed by Chris Mason
parent 9036c10208
commit 6643558db2
4 changed files with 43 additions and 32 deletions
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31
fs/btrfs/file.c
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@@ -364,6 +364,7 @@ int noinline btrfs_drop_extents(struct btrfs_trans_handle *trans,
u64 start, u64 end, u64 inline_limit, u64 *hint_byte)
{
u64 extent_end = 0;
u64 locked_end = end;
u64 search_start = start;
u64 leaf_start;
u64 ram_bytes = 0;
@@ -479,12 +480,6 @@ next_slot:
goto next_slot;
}
if (found_inline) {
u64 mask = root->sectorsize - 1;
search_start = (extent_end + mask) & ~mask;
} else
search_start = extent_end;
if (end <= extent_end && start >= key.offset && found_inline)
*hint_byte = EXTENT_MAP_INLINE;
@@ -501,6 +496,26 @@ next_slot:
if (found_inline && start <= key.offset)
keep = 1;
}
if (bookend && found_extent && locked_end < extent_end) {
ret = try_lock_extent(&BTRFS_I(inode)->io_tree,
locked_end, extent_end - 1, GFP_NOFS);
if (!ret) {
btrfs_release_path(root, path);
lock_extent(&BTRFS_I(inode)->io_tree,
locked_end, extent_end - 1, GFP_NOFS);
locked_end = extent_end;
continue;
}
locked_end = extent_end;
}
if (found_inline) {
u64 mask = root->sectorsize - 1;
search_start = (extent_end + mask) & ~mask;
} else
search_start = extent_end;
/* truncate existing extent */
if (start > key.offset) {
u64 new_num;
@@ -638,6 +653,10 @@ next_slot:
}
out:
btrfs_free_path(path);
if (locked_end > end) {
unlock_extent(&BTRFS_I(inode)->io_tree, end, locked_end - 1,
GFP_NOFS);
}
btrfs_check_file(root, inode);
return ret;
}