[PATCH v2 2/7] radix-tree: Use local_lock for protection

Sebastian Andrzej Siewior
2020-05-24T21:58:19Z

The radix-tree and idr preload mechanisms use preempt_disable() to protect
the complete operation between xxx_preload() and xxx_preload_end().

As the code inside the preempt disabled section acquires regular spinlocks,
which are converted to 'sleeping' spinlocks on a PREEMPT_RT kernel and
eventually calls into a memory allocator, this conflicts with the RT
semantics.

Convert it to a local_lock which allows RT kernels to substitute them with
a real per CPU lock. On non RT kernels this maps to preempt_disable() as
before, but provides also lockdep coverage of the critical region.
No functional change.

Cc: Matthew Wilcox <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/idr.h | 5 +----
include/linux/radix-tree.h | 6 +-----
lib/radix-tree.c | 29 ++++++++++++++++++++++-------
3 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/include/linux/idr.h b/include/linux/idr.h
index ac6e946b6767b..839da8f2f6f13 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -169,10 +169,7 @@ static inline bool idr_is_empty(const struct idr *idr)
* Each idr_preload() should be matched with an invocation of this
* function. See idr_preload() for details.
*/
-static inline void idr_preload_end(void)
-{
- preempt_enable();
-}
+void idr_preload_end(void);

/**
* idr_for_each_entry() - Iterate over an IDR's elements of a given type.
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 63e62372443a5..040b1fd0ab940 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -226,6 +226,7 @@ unsigned int radix_tree_gang_lookup(const struct radix_tree_root *,
unsigned int max_items);
int radix_tree_preload(gfp_t gfp_mask);
int radix_tree_maybe_preload(gfp_t gfp_mask);
+void radix_tree_preload_end(void);
void radix_tree_init(void);
void *radix_tree_tag_set(struct radix_tree_root *,
unsigned long index, unsigned int tag);
@@ -243,11 +244,6 @@ unsigned int radix_tree_gang_lookup_tag_slot(const struct radix_tree_root *,
unsigned int max_items, unsigned int tag);
int radix_tree_tagged(const struct radix_tree_root *, unsigned int tag);

-static inline void radix_tree_preload_end(void)
-{
- preempt_enable();
-}
-
void __rcu **idr_get_free(struct radix_tree_root *root,
struct radix_tree_iter *iter, gfp_t gfp,
unsigned long max);
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 2ee6ae3b0ade0..609aeb900b550 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -20,6 +20,7 @@
#include <linux/kernel.h>
#include <linux/kmemleak.h>
#include <linux/percpu.h>
+#include <linux/locallock.h>
#include <linux/preempt.h> /* in_interrupt() */
#include <linux/radix-tree.h>
#include <linux/rcupdate.h>
@@ -27,7 +28,6 @@
#include <linux/string.h>
#include <linux/xarray.h>

-
/*
* Radix tree node cache.
*/
@@ -59,11 +59,14 @@ struct kmem_cache *radix_tree_node_cachep;
* Per-cpu pool of preloaded nodes
*/
struct radix_tree_preload {
+ struct local_lock lock;
unsigned nr;
/* nodes->parent points to next preallocated node */
struct radix_tree_node *nodes;
};
-static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
+static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) =
+ { .lock = INIT_LOCAL_LOCK(lock),
+ .nr = 0, };

static inline struct radix_tree_node *entry_to_node(void *ptr)
{
@@ -332,14 +335,14 @@ static __must_check int __radix_tree_preload(gfp_t gfp_mask, unsigned nr)
*/
gfp_mask &= ~__GFP_ACCOUNT;

- preempt_disable();
+ local_lock(&radix_tree_preloads.lock);
rtp = this_cpu_ptr(&radix_tree_preloads);
while (rtp->nr < nr) {
- preempt_enable();
+ local_unlock(&radix_tree_preloads.lock);
node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
if (node == NULL)
goto out;
- preempt_disable();
+ local_lock(&radix_tree_preloads.lock);
rtp = this_cpu_ptr(&radix_tree_preloads);
if (rtp->nr < nr) {
node->parent = rtp->nodes;
@@ -381,11 +384,17 @@ int radix_tree_maybe_preload(gfp_t gfp_mask)
if (gfpflags_allow_blocking(gfp_mask))
return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
/* Preloading doesn't help anything with this gfp mask, skip it */
- preempt_disable();
+ local_lock(&radix_tree_preloads.lock);
return 0;
}
EXPORT_SYMBOL(radix_tree_maybe_preload);

+void radix_tree_preload_end(void)
+{
+ local_unlock(&radix_tree_preloads.lock);
+}
+EXPORT_SYMBOL(radix_tree_preload_end);
+
static unsigned radix_tree_load_root(const struct radix_tree_root *root,
struct radix_tree_node **nodep, unsigned long *maxindex)
{
@@ -1470,10 +1479,16 @@ EXPORT_SYMBOL(radix_tree_tagged);
void idr_preload(gfp_t gfp_mask)
{
if (__radix_tree_preload(gfp_mask, IDR_PRELOAD_SIZE))
- preempt_disable();
+ local_lock(&radix_tree_preloads.lock);
}
EXPORT_SYMBOL(idr_preload);

+void idr_preload_end(void)
+{
+ local_unlock(&radix_tree_preloads.lock);
+}
+EXPORT_SYMBOL(idr_preload_end);
+
void __rcu **idr_get_free(struct radix_tree_root *root,
struct radix_tree_iter *iter, gfp_t gfp,
unsigned long max)
--
2.27.0.rc0