linux-kernel - [PATCH v3 1/3] mm/shmem: add __rcu annotations and properly deref radix entry

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Date:   Mon,  9 Apr 2018 16:05:03 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Marc-André Lureau <marcandre.lureau@...il.com>,
        David Herrmann <dh.herrmann@...il.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH v3 1/3] mm/shmem: add __rcu annotations and properly deref radix entry

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.kravetz@...cle.com>
Signed-off-by: Matthew Wilcox <willy@...radead.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