tmpfs: no need to use i_lock

2.6.36's 7e496299d4d2 ("tmpfs: make tmpfs scalable with percpu_counter for
used blocks") to make tmpfs scalable with percpu_counter used
inode->i_lock in place of sbinfo->stat_lock around i_blocks updates; but
that was adverse to scalability, and unnecessary, since info->lock is
already held there in the fast paths.

Remove those uses of i_lock, and add info->lock in the three error paths
where it's then needed across shmem_free_blocks().  It's not actually
needed across shmem_unacct_blocks(), but they're so often paired that it
looks wrong to split them apart.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 8 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index fcedf5464eb7..c1db11cf220d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -241,9 +241,7 @@ static void shmem_free_blocks(struct inode *inode, long pages)
         struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
         if (sbinfo->max_blocks) {
                 percpu_counter_add(&sbinfo->used_blocks, -pages);
-                spin_lock(&inode->i_lock);
                 inode->i_blocks -= pages*BLOCKS_PER_PAGE;
-                spin_unlock(&inode->i_lock);
         }
 }
 
@@ -432,9 +430,7 @@ static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long
                                                 sbinfo->max_blocks - 1) >= 0)
                                 return ERR_PTR(-ENOSPC);
                         percpu_counter_inc(&sbinfo->used_blocks);
-                        spin_lock(&inode->i_lock);
                         inode->i_blocks += BLOCKS_PER_PAGE;
-                        spin_unlock(&inode->i_lock);
                 }
 
                 spin_unlock(&info->lock);
@@ -1421,9 +1417,7 @@ repeat:
                             shmem_acct_block(info->flags))
                                 goto nospace;
                         percpu_counter_inc(&sbinfo->used_blocks);
-                        spin_lock(&inode->i_lock);
                         inode->i_blocks += BLOCKS_PER_PAGE;
-                        spin_unlock(&inode->i_lock);
                 } else if (shmem_acct_block(info->flags))
                         goto nospace;
 
@@ -1434,8 +1428,10 @@ repeat:
                                 spin_unlock(&info->lock);
                                 filepage = shmem_alloc_page(gfp, info, idx);
                                 if (!filepage) {
+                                        spin_lock(&info->lock);
                                         shmem_unacct_blocks(info->flags, 1);
                                         shmem_free_blocks(inode, 1);
+                                        spin_unlock(&info->lock);
                                         error = -ENOMEM;
                                         goto failed;
                                 }
@@ -1449,8 +1445,10 @@ repeat:
                                         current->mm, GFP_KERNEL);
                                 if (error) {
                                         page_cache_release(filepage);
+                                        spin_lock(&info->lock);
                                         shmem_unacct_blocks(info->flags, 1);
                                         shmem_free_blocks(inode, 1);
+                                        spin_unlock(&info->lock);
                                         filepage = NULL;
                                         goto failed;
                                 }
@@ -1480,10 +1478,10 @@ repeat:
                          * be done automatically.
                          */
                         if (ret) {
-                                spin_unlock(&info->lock);
-                                page_cache_release(filepage);
                                 shmem_unacct_blocks(info->flags, 1);
                                 shmem_free_blocks(inode, 1);
+                                spin_unlock(&info->lock);
+                                page_cache_release(filepage);
                                 filepage = NULL;
                                 if (error)
                                         goto failed;