This sounds sort of impossible but it is the only thing I can think of and at the very least it is theoretically possible so here it goes.
If we are in try_release_extent_buffer we will check that the ref count on the extent buffer is 1 and not under IO, and then go down and clear the tree ref. If between this check and clearing the tree ref somebody else comes in and grabs a ref on the eb and the marks it dirty before try_release_extent_buffer() does it's tree ref clear we can end up with a dirty eb that will be freed while it is still dirty which will result in a panic. Thanks, Signed-off-by: Josef Bacik <[email protected]> --- fs/btrfs/extent_io.c | 9 +++------ 1 files changed, 3 insertions(+), 6 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index b778fc2..20440ea 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4142,11 +4142,10 @@ static void check_buffer_tree_ref(struct extent_buffer *eb) * So bump the ref count first, then set the bit. If someone * beat us to it, drop the ref we added. */ - if (!test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) { + spin_lock(&eb->refs_lock); + if (!test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) atomic_inc(&eb->refs); - if (test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) - atomic_dec(&eb->refs); - } + spin_unlock(&eb->refs_lock); } static void mark_extent_buffer_accessed(struct extent_buffer *eb) @@ -4258,9 +4257,7 @@ again: goto free_eb; } /* add one reference for the tree */ - spin_lock(&eb->refs_lock); check_buffer_tree_ref(eb); - spin_unlock(&eb->refs_lock); spin_unlock(&tree->buffer_lock); radix_tree_preload_end(); -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
