fs: dcache scale subdirs

Protect d_subdirs and d_child with d_lock, except in filesystems that aren't
using dcache_lock for these anyway (eg. using i_mutex).

Note: if we change the locking rule in future so that ->d_child protection is
provided only with ->d_parent->d_lock, it may allow us to reduce some locking.
But it would be an exception to an otherwise regular locking scheme, so we'd
have to see some good results. Probably not worthwhile.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 16 insertions, 2 deletions

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 7922509b5b2..7a9ed6b8829 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -143,10 +143,13 @@ static int autofs4_dir_open(struct inode *inode, struct file *file)
          * it.
          */
         spin_lock(&dcache_lock);
+        spin_lock(&dentry->d_lock);
         if (!d_mountpoint(dentry) && list_empty(&dentry->d_subdirs)) {
+                spin_unlock(&dentry->d_lock);
                 spin_unlock(&dcache_lock);
                 return -ENOENT;
         }
+        spin_unlock(&dentry->d_lock);
         spin_unlock(&dcache_lock);
 
 out:
@@ -253,7 +256,9 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
         lookup_type = autofs4_need_mount(nd->flags);
         spin_lock(&sbi->fs_lock);
         spin_lock(&dcache_lock);
+        spin_lock(&dentry->d_lock);
         if (!(lookup_type || ino->flags & AUTOFS_INF_PENDING)) {
+                spin_unlock(&dentry->d_lock);
                 spin_unlock(&dcache_lock);
                 spin_unlock(&sbi->fs_lock);
                 goto follow;
@@ -266,6 +271,7 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
          */
         if (ino->flags & AUTOFS_INF_PENDING ||
             (!d_mountpoint(dentry) && list_empty(&dentry->d_subdirs))) {
+                spin_unlock(&dentry->d_lock);
                 spin_unlock(&dcache_lock);
                 spin_unlock(&sbi->fs_lock);
 
@@ -275,6 +281,7 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
 
                 goto follow;
         }
+        spin_unlock(&dentry->d_lock);
         spin_unlock(&dcache_lock);
         spin_unlock(&sbi->fs_lock);
 follow:
@@ -347,10 +354,12 @@ static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
 
         /* Check for a non-mountpoint directory with no contents */
         spin_lock(&dcache_lock);
+        spin_lock(&dentry->d_lock);
         if (S_ISDIR(dentry->d_inode->i_mode) &&
             !d_mountpoint(dentry) && list_empty(&dentry->d_subdirs)) {
                 DPRINTK("dentry=%p %.*s, emptydir",
                          dentry, dentry->d_name.len, dentry->d_name.name);
+                spin_unlock(&dentry->d_lock);
                 spin_unlock(&dcache_lock);
 
                 /* The daemon never causes a mount to trigger */
@@ -367,6 +376,7 @@ static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
 
                 return status;
         }
+        spin_unlock(&dentry->d_lock);
         spin_unlock(&dcache_lock);
 
         return 1;
@@ -776,12 +786,16 @@ static int autofs4_dir_rmdir(struct inode *dir, struct dentry *dentry)
                 return -EACCES;
 
         spin_lock(&dcache_lock);
+        spin_lock(&sbi->lookup_lock);
+        spin_lock(&dentry->d_lock);
         if (!list_empty(&dentry->d_subdirs)) {
+                spin_unlock(&dentry->d_lock);
+                spin_unlock(&sbi->lookup_lock);
                 spin_unlock(&dcache_lock);
                 return -ENOTEMPTY;
         }
-        autofs4_add_expiring(dentry);
-        spin_lock(&dentry->d_lock);
+        __autofs4_add_expiring(dentry);
+        spin_unlock(&sbi->lookup_lock);
         __d_drop(dentry);
         spin_unlock(&dentry->d_lock);
         spin_unlock(&dcache_lock);