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btrfs-progs: Fix bus error on sparc

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Currently, as of 8cae1840af when running
btrfs-convert I get a bus error.

The problem is that struct btrfs_key has __attribute__ ((__packed__))
so it is not aligned. Then, a pointer to it's objectid field is taken,
cast to a  void*, then eventually cast back to a u64* and
dereferenced. The problem is that the dereferenced u64* is not
necessarily aligned (ie, not necessarily a valid u64*), resulting in
undefined behavior.

This patch adds a local u64 variable which would of course be properly
aligned and then uses a pointer to that.

I did not modify the call from btrfs_fs_roots_compare_roots as that
uses struct btrfs_root which is a regular struct and would thus have
it's members correctly aligned to begin with.

After patching this I realized Liu Bo had already written a similar
patch, but I think mine is cleaner, so I'm sending it anyway.

Signed-off-by: Ivan Jager <aij+@mrph.org>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Ivan Jager 2014-01-17 15:00:43 +01:00 committed by Chris Mason
parent ef3f6124f0
commit 0511ca4b50
1 changed files with 2 additions and 1 deletions
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3
disk-io.c
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@ -683,6 +683,7 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info,
struct btrfs_root *root;
struct rb_node *node;
int ret;
u64 objectid = location->objectid;
if (location->objectid == BTRFS_ROOT_TREE_OBJECTID)
return fs_info->tree_root;
@ -698,7 +699,7 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info,
BUG_ON(location->objectid == BTRFS_TREE_RELOC_OBJECTID ||
location->offset != (u64)-1);
node = rb_search(&fs_info->fs_root_tree, (void *)&location->objectid,
node = rb_search(&fs_info->fs_root_tree, (void *)&objectid,
btrfs_fs_roots_compare_objectids, NULL);
if (node)
return container_of(node, struct btrfs_root, rb_node);