1 files changed, 58 insertions, 135 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 4ce02e0673db..bd106361be4b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -264,46 +264,55 @@ static int shmem_radix_tree_replace(struct address_space *mapping,
 }
 
 /*
+ * Sometimes, before we decide whether to proceed or to fail, we must check
+ * that an entry was not already brought back from swap by a racing thread.
+ *
+ * Checking page is not enough: by the time a SwapCache page is locked, it
+ * might be reused, and again be SwapCache, using the same swap as before.
+ */
+static bool shmem_confirm_swap(struct address_space *mapping,
+                               pgoff_t index, swp_entry_t swap)
+{
+        void *item;
+
+        rcu_read_lock();
+        item = radix_tree_lookup(&mapping->page_tree, index);
+        rcu_read_unlock();
+        return item == swp_to_radix_entry(swap);
+}
+
+/*
  * Like add_to_page_cache_locked, but error if expected item has gone.
  */
 static int shmem_add_to_page_cache(struct page *page,
                                    struct address_space *mapping,
                                    pgoff_t index, gfp_t gfp, void *expected)
 {
-        int error = 0;
+        int error;
 
         VM_BUG_ON(!PageLocked(page));
         VM_BUG_ON(!PageSwapBacked(page));
 
+        page_cache_get(page);
+        page->mapping = mapping;
+        page->index = index;
+
+        spin_lock_irq(&mapping->tree_lock);
         if (!expected)
-                error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
+                error = radix_tree_insert(&mapping->page_tree, index, page);
+        else
+                error = shmem_radix_tree_replace(mapping, index, expected,
+                                                                 page);
         if (!error) {
-                page_cache_get(page);
-                page->mapping = mapping;
-                page->index = index;
-
-                spin_lock_irq(&mapping->tree_lock);
-                if (!expected)
-                        error = radix_tree_insert(&mapping->page_tree,
-                                                        index, page);
-                else
-                        error = shmem_radix_tree_replace(mapping, index,
-                                                        expected, page);
-                if (!error) {
-                        mapping->nrpages++;
-                        __inc_zone_page_state(page, NR_FILE_PAGES);
-                        __inc_zone_page_state(page, NR_SHMEM);
-                        spin_unlock_irq(&mapping->tree_lock);
-                } else {
-                        page->mapping = NULL;
-                        spin_unlock_irq(&mapping->tree_lock);
-                        page_cache_release(page);
-                }
-                if (!expected)
-                        radix_tree_preload_end();
+                mapping->nrpages++;
+                __inc_zone_page_state(page, NR_FILE_PAGES);
+                __inc_zone_page_state(page, NR_SHMEM);
+                spin_unlock_irq(&mapping->tree_lock);
+        } else {
+                page->mapping = NULL;
+                spin_unlock_irq(&mapping->tree_lock);
+                page_cache_release(page);
         }
-        if (error)
-                mem_cgroup_uncharge_cache_page(page);
         return error;
 }
 
@@ -1124,9 +1133,9 @@ repeat:
                 /* We have to do this with page locked to prevent races */
                 lock_page(page);
                 if (!PageSwapCache(page) || page_private(page) != swap.val ||
-                    page->mapping) {
+                    !shmem_confirm_swap(mapping, index, swap)) {
                         error = -EEXIST;        /* try again */
-                        goto failed;
+                        goto unlock;
                 }
                 if (!PageUptodate(page)) {
                         error = -EIO;
@@ -1142,9 +1151,12 @@ repeat:
 
                 error = mem_cgroup_cache_charge(page, current->mm,
                                                 gfp & GFP_RECLAIM_MASK);
-                if (!error)
+                if (!error) {
                         error = shmem_add_to_page_cache(page, mapping, index,
                                                 gfp, swp_to_radix_entry(swap));
+                        /* We already confirmed swap, and make no allocation */
+                        VM_BUG_ON(error);
+                }
                 if (error)
                         goto failed;
 
@@ -1181,11 +1193,18 @@ repeat:
                 __set_page_locked(page);
                 error = mem_cgroup_cache_charge(page, current->mm,
                                                 gfp & GFP_RECLAIM_MASK);
-                if (!error)
-                        error = shmem_add_to_page_cache(page, mapping, index,
-                                                gfp, NULL);
                 if (error)
                         goto decused;
+                error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
+                if (!error) {
+                        error = shmem_add_to_page_cache(page, mapping, index,
+                                                        gfp, NULL);
+                        radix_tree_preload_end();
+                }
+                if (error) {
+                        mem_cgroup_uncharge_cache_page(page);
+                        goto decused;
+                }
                 lru_cache_add_anon(page);
 
                 spin_lock(&info->lock);
@@ -1245,14 +1264,10 @@ decused:
 unacct:
         shmem_unacct_blocks(info->flags, 1);
 failed:
-        if (swap.val && error != -EINVAL) {
-                struct page *test = find_get_page(mapping, index);
-                if (test && !radix_tree_exceptional_entry(test))
-                        page_cache_release(test);
-                /* Have another try if the entry has changed */
-                if (test != swp_to_radix_entry(swap))
-                        error = -EEXIST;
-        }
+        if (swap.val && error != -EINVAL &&
+            !shmem_confirm_swap(mapping, index, swap))
+                error = -EEXIST;
+unlock:
         if (page) {
                 unlock_page(page);
                 page_cache_release(page);
@@ -1264,7 +1279,7 @@ failed:
                 spin_unlock(&info->lock);
                 goto repeat;
         }
-        if (error == -EEXIST)
+        if (error == -EEXIST)   /* from above or from radix_tree_insert */
                 goto repeat;
         return error;
 }
@@ -1692,98 +1707,6 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
         return error;
 }
 
-/*
- * llseek SEEK_DATA or SEEK_HOLE through the radix_tree.
- */
-static pgoff_t shmem_seek_hole_data(struct address_space *mapping,
-                                    pgoff_t index, pgoff_t end, int origin)
-{
-        struct page *page;
-        struct pagevec pvec;
-        pgoff_t indices[PAGEVEC_SIZE];
-        bool done = false;
-        int i;
-
-        pagevec_init(&pvec, 0);
-        pvec.nr = 1;            /* start small: we may be there already */
-        while (!done) {
-                pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
-                                        pvec.nr, pvec.pages, indices);
-                if (!pvec.nr) {
-                        if (origin == SEEK_DATA)
-                                index = end;
-                        break;
-                }
-                for (i = 0; i < pvec.nr; i++, index++) {
-                        if (index < indices[i]) {
-                                if (origin == SEEK_HOLE) {
-                                        done = true;
-                                        break;
-                                }
-                                index = indices[i];
-                        }
-                        page = pvec.pages[i];
-                        if (page && !radix_tree_exceptional_entry(page)) {
-                                if (!PageUptodate(page))
-                                        page = NULL;
-                        }
-                        if (index >= end ||
-                            (page && origin == SEEK_DATA) ||
-                            (!page && origin == SEEK_HOLE)) {
-                                done = true;
-                                break;
-                        }
-                }
-                shmem_deswap_pagevec(&pvec);
-                pagevec_release(&pvec);
-                pvec.nr = PAGEVEC_SIZE;
-                cond_resched();
-        }
-        return index;
-}
-
-static loff_t shmem_file_llseek(struct file *file, loff_t offset, int origin)
-{
-        struct address_space *mapping;
-        struct inode *inode;
-        pgoff_t start, end;
-        loff_t new_offset;
-
-        if (origin != SEEK_DATA && origin != SEEK_HOLE)
-                return generic_file_llseek_size(file, offset, origin,
-                                                        MAX_LFS_FILESIZE);
-        mapping = file->f_mapping;
-        inode = mapping->host;
-        mutex_lock(&inode->i_mutex);
-        /* We're holding i_mutex so we can access i_size directly */
-
-        if (offset < 0)
-                offset = -EINVAL;
-        else if (offset >= inode->i_size)
-                offset = -ENXIO;
-        else {
-                start = offset >> PAGE_CACHE_SHIFT;
-                end = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
-                new_offset = shmem_seek_hole_data(mapping, start, end, origin);
-                new_offset <<= PAGE_CACHE_SHIFT;
-                if (new_offset > offset) {
-                        if (new_offset < inode->i_size)
-                                offset = new_offset;
-                        else if (origin == SEEK_DATA)
-                                offset = -ENXIO;
-                        else
-                                offset = inode->i_size;
-                }
-        }
-
-        if (offset >= 0 && offset != file->f_pos) {
-                file->f_pos = offset;
-                file->f_version = 0;
-        }
-        mutex_unlock(&inode->i_mutex);
-        return offset;
-}
-
 static long shmem_fallocate(struct file *file, int mode, loff_t offset,
                                                          loff_t len)
 {
@@ -2787,7 +2710,7 @@ static const struct address_space_operations shmem_aops = {
 static const struct file_operations shmem_file_operations = {
         .mmap           = shmem_mmap,
 #ifdef CONFIG_TMPFS
-        .llseek         = shmem_file_llseek,
+        .llseek         = generic_file_llseek,
         .read           = do_sync_read,
         .write          = do_sync_write,
         .aio_read       = shmem_file_aio_read,