NFS: Fix put_nfs_open_context

We need to grab the inode->i_lock atomically with the last reference put in
order to remove the open context that is being freed from the
nfsi->open_files list.

Fix by converting the kref to a standard atomic counter and then using
atomic_dec_and_lock()...

Thanks to Arnd Bergmann for pointing out the problem.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 8 insertions, 16 deletions

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index bca6cdcb9f0d..71a49c3acabd 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -468,7 +468,7 @@ static struct nfs_open_context *alloc_nfs_open_context(struct vfsmount *mnt, str
                 ctx->lockowner = current->files;
                 ctx->error = 0;
                 ctx->dir_cookie = 0;
-                kref_init(&ctx->kref);
+                atomic_set(&ctx->count, 1);
         }
         return ctx;
 }
@@ -476,21 +476,18 @@ static struct nfs_open_context *alloc_nfs_open_context(struct vfsmount *mnt, str
 struct nfs_open_context *get_nfs_open_context(struct nfs_open_context *ctx)
 {
         if (ctx != NULL)
-                kref_get(&ctx->kref);
+                atomic_inc(&ctx->count);
         return ctx;
 }
 
-static void nfs_free_open_context(struct kref *kref)
+void put_nfs_open_context(struct nfs_open_context *ctx)
 {
-        struct nfs_open_context *ctx = container_of(kref,
-                        struct nfs_open_context, kref);
+        struct inode *inode = ctx->path.dentry->d_inode;
 
-        if (!list_empty(&ctx->list)) {
-                struct inode *inode = ctx->path.dentry->d_inode;
-                spin_lock(&inode->i_lock);
-                list_del(&ctx->list);
-                spin_unlock(&inode->i_lock);
-        }
+        if (!atomic_dec_and_lock(&ctx->count, &inode->i_lock))
+                return;
+        list_del(&ctx->list);
+        spin_unlock(&inode->i_lock);
         if (ctx->state != NULL)
                 nfs4_close_state(&ctx->path, ctx->state, ctx->mode);
         if (ctx->cred != NULL)
@@ -500,11 +497,6 @@ static void nfs_free_open_context(struct kref *kref)
         kfree(ctx);
 }
 
-void put_nfs_open_context(struct nfs_open_context *ctx)
-{
-        kref_put(&ctx->kref, nfs_free_open_context);
-}
-
 /*
  * Ensure that mmap has a recent RPC credential for use when writing out
  * shared pages