[3.19.y-ckt stable] Patch "radix-tree: fix race in gang lookup" has been added to the 3.19.y-ckt tree
Kamal Mostafa
kamal at canonical.com
Wed Mar 9 00:22:18 UTC 2016
This is a note to let you know that I have just added a patch titled
radix-tree: fix race in gang lookup
to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue
This patch is scheduled to be released in version 3.19.8-ckt16.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
---8<------------------------------------------------------------
>From 8744be13299582325250b917428a208249b2f813 Mon Sep 17 00:00:00 2001
From: Matthew Wilcox <willy at linux.intel.com>
Date: Tue, 2 Feb 2016 16:57:52 -0800
Subject: radix-tree: fix race in gang lookup
commit 46437f9a554fbe3e110580ca08ab703b59f2f95a upstream.
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 <willy at linux.intel.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: Ohad Ben-Cohen <ohad at wizery.com>
Cc: Konstantin Khlebnikov <khlebnikov at openvz.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
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 3291a8e..b31e22d 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;
}
--
2.7.0
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