[added to the 4.1 stable tree] radix-tree: fix race in gang lookup
From: Sasha Levin <hidden>
Date: 2016-02-10 15:14:45
Subsystem:
library code, the rest · Maintainers:
Andrew Morton, Linus Torvalds
From: Matthew Wilcox <redacted>
This patch has been added to the 4.1 stable tree. If you have any
objections, please let us know.
===============
[ Upstream commit 46437f9a554fbe3e110580ca08ab703b59f2f95a ]
If the indirect_ptr bit is set on a slot, that indicates we need to redo
the lookup. Introduce a new function radix_tree_iter_retry() which
forces the loop to retry the lookup by setting 'slot' to NULL and
turning the iterator back to point at the problematic entry.
This is a pretty rare problem to hit at the moment; the lookup has to
race with a grow of the radix tree from a height of 0. The consequences
of hitting this race are that gang lookup could return a pointer to a
radix_tree_node instead of a pointer to whatever the user had inserted
in the tree.
Fixes: cebbd29e1c2f ("radix-tree: rewrite gang lookup using iterator")
Signed-off-by: Matthew Wilcox <redacted>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ohad Ben-Cohen <redacted>
Cc: Konstantin Khlebnikov <redacted>
Cc: <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <redacted>
---
include/linux/radix-tree.h | 16 ++++++++++++++++
lib/radix-tree.c | 12 ++++++++++--
2 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 33170db..1a2b227 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h@@ -370,6 +370,22 @@ void **radix_tree_next_chunk(struct radix_tree_root *root, struct radix_tree_iter *iter, unsigned flags); /** + * radix_tree_iter_retry - retry this chunk of the iteration + * @iter: iterator state + * + * If we iterate over a tree protected only by the RCU lock, a race + * against deletion or creation may result in seeing a slot for which + * radix_tree_deref_retry() returns true. If so, call this function + * and continue the iteration. + */ +static inline __must_check +void **radix_tree_iter_retry(struct radix_tree_iter *iter) +{ + iter->next_index = iter->index; + return NULL; +} + +/** * radix_tree_chunk_size - get current chunk size * * @iter: pointer to radix tree iterator
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 3d2aa27..8399002 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c@@ -1014,9 +1014,13 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results, return 0; radix_tree_for_each_slot(slot, root, &iter, first_index) { - results[ret] = indirect_to_ptr(rcu_dereference_raw(*slot)); + results[ret] = rcu_dereference_raw(*slot); if (!results[ret]) continue; + if (radix_tree_is_indirect_ptr(results[ret])) { + slot = radix_tree_iter_retry(&iter); + continue; + } if (++ret == max_items) break; }
@@ -1093,9 +1097,13 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results, return 0; radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) { - results[ret] = indirect_to_ptr(rcu_dereference_raw(*slot)); + results[ret] = rcu_dereference_raw(*slot); if (!results[ret]) continue; + if (radix_tree_is_indirect_ptr(results[ret])) { + slot = radix_tree_iter_retry(&iter); + continue; + } if (++ret == max_items) break; }
--
2.5.0