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, 3 insertions, 0 deletions

diff --git a/fs/ncpfs/dir.c b/fs/ncpfs/dir.c
index bbbf7922f422..102278ed38bd 100644
--- a/fs/ncpfs/dir.c
+++ b/fs/ncpfs/dir.c
@@ -392,6 +392,7 @@ ncp_dget_fpos(struct dentry *dentry, struct dentry *parent, unsigned long fpos)
 
         /* If a pointer is invalid, we search the dentry. */
         spin_lock(&dcache_lock);
+        spin_lock(&parent->d_lock);
         next = parent->d_subdirs.next;
         while (next != &parent->d_subdirs) {
                 dent = list_entry(next, struct dentry, d_u.d_child);
@@ -400,11 +401,13 @@ ncp_dget_fpos(struct dentry *dentry, struct dentry *parent, unsigned long fpos)
                                 dget_locked(dent);
                         else
                                 dent = NULL;
+                        spin_unlock(&parent->d_lock);
                         spin_unlock(&dcache_lock);
                         goto out;
                 }
                 next = next->next;
         }
+        spin_unlock(&parent->d_lock);
         spin_unlock(&dcache_lock);
         return NULL;