fs-dcache-scale-d_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).

XXX: probably don't need parent lock in inotify (because child lock
should stabilize parent). Also, possibly some filesystems don't need so
much locking (eg. of child dentry when modifying d_child, so long as
parent is locked)... but be on the safe side. Hmm, maybe we should just
say d_child list is protected by d_parent->d_lock. d_parent could remain
protected with d_lock.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
index d0a3de247458..cf6192583b73 100644
--- a/fs/autofs4/inode.c
+++ b/fs/autofs4/inode.c
@@ -113,6 +113,7 @@ static void autofs4_force_release(struct autofs_sb_info *sbi)
 
         spin_lock(&dcache_lock);
 repeat:
+        spin_lock(&this_parent->d_lock);
         next = this_parent->d_subdirs.next;
 resume:
         while (next != &this_parent->d_subdirs) {
@@ -125,11 +126,13 @@ resume:
                 }
 
                 if (!list_empty(&dentry->d_subdirs)) {
+                        spin_unlock(&this_parent->d_lock);
                         this_parent = dentry;
                         goto repeat;
                 }
 
                 next = next->next;
+                spin_unlock(&this_parent->d_lock);
                 spin_unlock(&dcache_lock);
 
                 DPRINTK("dentry %p %.*s",
@@ -137,20 +140,24 @@ resume:
 
                 dput(dentry);
                 spin_lock(&dcache_lock);
+                spin_lock(&this_parent->d_lock);
         }
 
         if (this_parent != sbi->sb->s_root) {
                 struct dentry *dentry = this_parent;
 
                 next = this_parent->d_u.d_child.next;
+                spin_unlock(&this_parent->d_lock);
                 this_parent = this_parent->d_parent;
                 spin_unlock(&dcache_lock);
                 DPRINTK("parent dentry %p %.*s",
                         dentry, (int)dentry->d_name.len, dentry->d_name.name);
                 dput(dentry);
                 spin_lock(&dcache_lock);
+                spin_lock(&this_parent->d_lock);
                 goto resume;
         }
+        spin_unlock(&this_parent->d_lock);
         spin_unlock(&dcache_lock);
 }