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, 5 insertions, 1 deletions

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index 571f270dca0f..2c924e8d85fe 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -113,6 +113,7 @@ static int __dcache_readdir(struct file *filp,
              last);
 
         spin_lock(&dcache_lock);
+        spin_lock(&parent->d_lock);
 
         /* start at beginning? */
         if (filp->f_pos == 2 || last == NULL ||
@@ -136,7 +137,7 @@ more:
                         fi->at_end = 1;
                         goto out_unlock;
                 }
-                spin_lock(&dentry->d_lock);
+                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
                 if (!d_unhashed(dentry) && dentry->d_inode &&
                     ceph_snap(dentry->d_inode) != CEPH_SNAPDIR &&
                     ceph_ino(dentry->d_inode) != CEPH_INO_CEPH &&
@@ -154,6 +155,7 @@ more:
 
         dget_dlock(dentry);
         spin_unlock(&dentry->d_lock);
+        spin_unlock(&parent->d_lock);
         spin_unlock(&dcache_lock);
 
         dout(" %llu (%llu) dentry %p %.*s %p\n", di->offset, filp->f_pos,
@@ -188,10 +190,12 @@ more:
         }
 
         spin_lock(&dcache_lock);
+        spin_lock(&parent->d_lock);
         p = p->prev;    /* advance to next dentry */
         goto more;
 
 out_unlock:
+        spin_unlock(&parent->d_lock);
         spin_unlock(&dcache_lock);
 out:
         if (last)