From 25b8b936ed44814a5ce6fc3b2a21401f33cd56f6 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Wed, 8 Jun 2011 14:36:54 -0400 Subject: [PATCH] Btrfs: don't map extent buffer if path->skip_locking is set Arne's scrub stuff exposed a problem with mapping the extent buffer in reada_for_search. He searches the commit root with multiple threads and with skip_locking set, so we can race and overwrite node->map_token since node isn't locked. So fix this so that we only map the extent buffer if we don't already have a map_token and skip_locking isn't set. Without this patch scrub would panic almost immediately, with the patch it doesn't panic anymore. Thanks, Reported-by: Arne Jansen Signed-off-by: Josef Bacik --- fs/btrfs/ctree.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index d84089349c82..2e667868e0d2 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -1228,6 +1228,7 @@ static void reada_for_search(struct btrfs_root *root, u32 nr; u32 blocksize; u32 nscan = 0; + bool map = true; if (level != 1) return; @@ -1249,8 +1250,11 @@ static void reada_for_search(struct btrfs_root *root, nritems = btrfs_header_nritems(node); nr = slot; + if (node->map_token || path->skip_locking) + map = false; + while (1) { - if (!node->map_token) { + if (map && !node->map_token) { unsigned long offset = btrfs_node_key_ptr_offset(nr); map_private_extent_buffer(node, offset, sizeof(struct btrfs_key_ptr), @@ -1277,7 +1281,7 @@ static void reada_for_search(struct btrfs_root *root, if ((search <= target && target - search <= 65536) || (search > target && search - target <= 65536)) { gen = btrfs_node_ptr_generation(node, nr); - if (node->map_token) { + if (map && node->map_token) { unmap_extent_buffer(node, node->map_token, KM_USER1); node->map_token = NULL; @@ -1289,7 +1293,7 @@ static void reada_for_search(struct btrfs_root *root, if ((nread > 65536 || nscan > 32)) break; } - if (node->map_token) { + if (map && node->map_token) { unmap_extent_buffer(node, node->map_token, KM_USER1); node->map_token = NULL; }