[PATCH v4 1/3] mm/shmem: add __rcu annotations and properly deref radix entry

[Mike Kravetz]

In preparation for memfd code restucture, clean up sparse warnings.
Most changes required adding __rcu annotations.  The routine
find_swap_entry was modified to properly deference radix tree
entries.

Signed-off-by: Mike Kravetz <mike.krav...@oracle.com>
Signed-off-by: Matthew Wilcox <wi...@infradead.org>
---
 mm/shmem.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index b85919243399..c7bad16fe884 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -327,7 +327,7 @@ static int shmem_radix_tree_replace(struct address_space 
*mapping,
                        pgoff_t index, void *expected, void *replacement)
 {
        struct radix_tree_node *node;
-       void **pslot;
+       void __rcu **pslot;
        void *item;
 
        VM_BUG_ON(!expected);
@@ -395,7 +395,7 @@ static bool shmem_confirm_swap(struct address_space 
*mapping,
 #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
 /* ifdef here to avoid bloating shmem.o when not necessary */
 
-int shmem_huge __read_mostly;
+static int shmem_huge __read_mostly;
 
 #if defined(CONFIG_SYSFS) || defined(CONFIG_TMPFS)
 static int shmem_parse_huge(const char *str)
@@ -682,7 +682,7 @@ unsigned long shmem_partial_swap_usage(struct address_space 
*mapping,
                                                pgoff_t start, pgoff_t end)
 {
        struct radix_tree_iter iter;
-       void **slot;
+       void __rcu **slot;
        struct page *page;
        unsigned long swapped = 0;
 
@@ -1098,13 +1098,19 @@ static void shmem_evict_inode(struct inode *inode)
 static unsigned long find_swap_entry(struct radix_tree_root *root, void *item)
 {
        struct radix_tree_iter iter;
-       void **slot;
+       void __rcu **slot;
        unsigned long found = -1;
        unsigned int checked = 0;
 
        rcu_read_lock();
        radix_tree_for_each_slot(slot, root, &iter, 0) {
-               if (*slot == item) {
+               void *entry = radix_tree_deref_slot(slot);
+
+               if (radix_tree_deref_retry(entry)) {
+                       slot = radix_tree_iter_retry(&iter);
+                       continue;
+               }
+               if (entry == item) {
                        found = iter.index;
                        break;
                }
@@ -2623,7 +2629,7 @@ static loff_t shmem_file_llseek(struct file *file, loff_t 
offset, int whence)
 static void shmem_tag_pins(struct address_space *mapping)
 {
        struct radix_tree_iter iter;
-       void **slot;
+       void __rcu **slot;
        pgoff_t start;
        struct page *page;
 
@@ -2665,7 +2671,7 @@ static void shmem_tag_pins(struct address_space *mapping)
 static int shmem_wait_for_pins(struct address_space *mapping)
 {
        struct radix_tree_iter iter;
-       void **slot;
+       void __rcu **slot;
        pgoff_t start;
        struct page *page;
        int error, scan;
-- 
2.13.6