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Subject[PATCH v2 2/2] Btrfs: fix unsafe usage of merge_state
merge_state can free the current state if it can be merged with the next node,
but in set_extent_bit(), after merge_state, we still use the current extent to
get the next node and cache it into cached_state

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
fs/btrfs/extent_io.c | 22 ++++++++++++++--------
1 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f36e284..129601e 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -780,20 +780,18 @@ hit_next:
if (err)
goto out;

+ next_node = rb_next(node);
cache_state(state, cached_state);
merge_state(tree, state);
if (last_end == (u64)-1)
goto out;

start = last_end + 1;
- if (start < end && prealloc && !need_resched()) {
- next_node = rb_next(node);
- if (next_node) {
- state = rb_entry(next_node, struct extent_state,
- rb_node);
- if (state->start == start)
- goto hit_next;
- }
+ if (next_node && start < end && prealloc && !need_resched()) {
+ state = rb_entry(next_node, struct extent_state,
+ rb_node);
+ if (state->start == start)
+ goto hit_next;
}
goto search_again;
}
@@ -856,14 +854,22 @@ hit_next:

prealloc = alloc_extent_state_atomic(prealloc);
BUG_ON(!prealloc);
+
+ /*
+ * Avoid to free 'prealloc' if it can be merged with
+ * the later extent.
+ */
+ atomic_inc(&prealloc->refs);
err = insert_state(tree, prealloc, start, this_end,
&bits);
BUG_ON(err == -EEXIST);
if (err) {
+ free_extent_state(prealloc);
prealloc = NULL;
goto out;
}
cache_state(prealloc, cached_state);
+ free_extent_state(prealloc);
prealloc = NULL;
start = this_end + 1;
goto search_again;
--
1.7.4.2


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