shmem: fix negative rss in memcg memory.stat

[mirror_ubuntu-zesty-kernel.git] / mm / shmem.c

diff --git a/mm/shmem.c b/mm/shmem.c
index 4ce02e0673db612befb63def38911d2d2b0638af..294364a24a1f62df16a2f86ca1b5f77dcc3f7aac 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -263,6 +263,24 @@ static int shmem_radix_tree_replace(struct address_space *mapping,
        return 0;
 }
 
+/*
+ * 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.
  */
@@ -1124,9 +1142,9 @@ 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 +1160,12 @@ 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;
 
@@ -1245,14 +1266,10 @@ 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 +1281,7 @@ 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 +1709,6 @@ 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 +2712,7 @@ 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,