tmpfs: open a window in shmem_unuse_inode

There are a couple of reasons (patches follow) why it would be good to open a
window for sleep in shmem_unuse_inode, between its search for a matching swap
entry, and its handling of the entry found.

shmem_unuse_inode must then use igrab to hold the inode against deletion in
that window, and its corresponding iput might result in deletion: so it had
better unlock_page before the iput, and might as well release the page too.

Nor is there any need to hold on to shmem_swaplist_mutex once we know we'll
leave the loop.  So this unwinding moves from try_to_unuse and shmem_unuse
into shmem_unuse_inode, in the case when it finds a match.

Let try_to_unuse break on error in the shmem_unuse case, as it does in the
unuse_mm case: though at this point in the series, no error to break on.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 22 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 2e03d6031c24..a0126c437105 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -838,10 +838,8 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
         if (size > SHMEM_NR_DIRECT)
                 size = SHMEM_NR_DIRECT;
         offset = shmem_find_swp(entry, ptr, ptr+size);
-        if (offset >= 0) {
-                shmem_swp_balance_unmap();
+        if (offset >= 0)
                 goto found;
-        }
         if (!info->i_indirect)
                 goto lost2;
 
@@ -879,11 +877,11 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
                         if (size > ENTRIES_PER_PAGE)
                                 size = ENTRIES_PER_PAGE;
                         offset = shmem_find_swp(entry, ptr, ptr+size);
+                        shmem_swp_unmap(ptr);
                         if (offset >= 0) {
                                 shmem_dir_unmap(dir);
                                 goto found;
                         }
-                        shmem_swp_unmap(ptr);
                 }
         }
 lost1:
@@ -893,10 +891,25 @@ lost2:
         return 0;
 found:
         idx += offset;
-        inode = &info->vfs_inode;
-        error = add_to_page_cache(page, inode->i_mapping, idx, GFP_ATOMIC);
+        inode = igrab(&info->vfs_inode);
+        spin_unlock(&info->lock);
+
+        /* move head to start search for next from here */
+        list_move_tail(&shmem_swaplist, &info->swaplist);
+        mutex_unlock(&shmem_swaplist_mutex);
+
+        error = 1;
+        if (!inode)
+                goto out;
+
+        spin_lock(&info->lock);
+        ptr = shmem_swp_entry(info, idx, NULL);
+        if (ptr && ptr->val == entry.val)
+                error = add_to_page_cache(page, inode->i_mapping,
+                                                idx, GFP_ATOMIC);
         if (error == -EEXIST) {
                 struct page *filepage = find_get_page(inode->i_mapping, idx);
+                error = 1;
                 if (filepage) {
                         /*
                          * There might be a more uptodate page coming down
@@ -911,16 +924,18 @@ found:
                 delete_from_swap_cache(page);
                 set_page_dirty(page);
                 info->flags |= SHMEM_PAGEIN;
-                shmem_swp_set(info, ptr + offset, 0);
+                shmem_swp_set(info, ptr, 0);
+                swap_free(entry);
+                error = 1;      /* not an error, but entry was found */
         }
-        shmem_swp_unmap(ptr);
+        if (ptr)
+                shmem_swp_unmap(ptr);
         spin_unlock(&info->lock);
-        /*
-         * Decrement swap count even when the entry is left behind:
-         * try_to_unuse will skip over mms, then reincrement count.
-         */
-        swap_free(entry);
-        return 1;
+out:
+        unlock_page(page);
+        page_cache_release(page);
+        iput(inode);            /* allows for NULL */
+        return error;
 }
 
 /*
@@ -935,18 +950,16 @@ int shmem_unuse(swp_entry_t entry, struct page *page)
         mutex_lock(&shmem_swaplist_mutex);
         list_for_each_safe(p, next, &shmem_swaplist) {
                 info = list_entry(p, struct shmem_inode_info, swaplist);
-                if (!info->swapped)
+                if (info->swapped)
+                        found = shmem_unuse_inode(info, entry, page);
+                else
                         list_del_init(&info->swaplist);
-                else if (shmem_unuse_inode(info, entry, page)) {
-                        /* move head to start search for next from here */
-                        list_move_tail(&shmem_swaplist, &info->swaplist);
-                        found = 1;
-                        break;
-                }
                 cond_resched();
+                if (found)
+                        goto out;
         }
         mutex_unlock(&shmem_swaplist_mutex);
-        return found;
+out:    return found;   /* 0 or 1 or -ENOMEM */
 }
 
 /*