locking in fs/9p ->readdir()

	... is really excessive.  First of all, ->readdir() is serialized by
file->f_path.dentry->d_inode->i_mutex; playing with file->f_path.dentry->d_lock
is not buying you anything.  Moreover, rdir->mutex is pointless for exactly
the same reason - you'll never see contention on it.

	While we are at it, there's no point in having rdir->buf a pointer -
you have it point just past the end of rdir, so it might as well be a flex
array (and no, it's not a gccism).

	Absolutely untested patch follows:

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

1 files changed, 23 insertions, 69 deletions

diff --git a/fs/9p/vfs_dir.c b/fs/9p/vfs_dir.c
index ff911e779651..be1e34adc3c6 100644
--- a/fs/9p/vfs_dir.c
+++ b/fs/9p/vfs_dir.c
@@ -52,10 +52,9 @@
  */
 
 struct p9_rdir {
-        struct mutex mutex;
         int head;
         int tail;
-        uint8_t *buf;
+        uint8_t buf[];
 };
 
 /**
@@ -93,33 +92,12 @@ static void p9stat_init(struct p9_wstat *stbuf)
  *
  */
 
-static int v9fs_alloc_rdir_buf(struct file *filp, int buflen)
+static struct p9_rdir *v9fs_alloc_rdir_buf(struct file *filp, int buflen)
 {
-        struct p9_rdir *rdir;
-        struct p9_fid *fid;
-        int err = 0;
-
-        fid = filp->private_data;
-        if (!fid->rdir) {
-                rdir = kmalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);
-
-                if (rdir == NULL) {
-                        err = -ENOMEM;
-                        goto exit;
-                }
-                spin_lock(&filp->f_dentry->d_lock);
-                if (!fid->rdir) {
-                        rdir->buf = (uint8_t *)rdir + sizeof(struct p9_rdir);
-                        mutex_init(&rdir->mutex);
-                        rdir->head = rdir->tail = 0;
-                        fid->rdir = (void *) rdir;
-                        rdir = NULL;
-                }
-                spin_unlock(&filp->f_dentry->d_lock);
-                kfree(rdir);
-        }
-exit:
-        return err;
+        struct p9_fid *fid = filp->private_data;
+        if (!fid->rdir)
+                fid->rdir = kzalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);
+        return fid->rdir;
 }
 
 /**
@@ -145,20 +123,16 @@ static int v9fs_dir_readdir(struct file *filp, void *dirent, filldir_t filldir)
 
         buflen = fid->clnt->msize - P9_IOHDRSZ;
 
-        err = v9fs_alloc_rdir_buf(filp, buflen);
-        if (err)
-                goto exit;
-        rdir = (struct p9_rdir *) fid->rdir;
+        rdir = v9fs_alloc_rdir_buf(filp, buflen);
+        if (!rdir)
+                return -ENOMEM;
 
-        err = mutex_lock_interruptible(&rdir->mutex);
-        if (err)
-                return err;
-        while (err == 0) {
+        while (1) {
                 if (rdir->tail == rdir->head) {
                         err = v9fs_file_readn(filp, rdir->buf, NULL,
                                                         buflen, filp->f_pos);
                         if (err <= 0)
-                                goto unlock_and_exit;
+                                return err;
 
                         rdir->head = 0;
                         rdir->tail = err;
@@ -169,9 +143,8 @@ static int v9fs_dir_readdir(struct file *filp, void *dirent, filldir_t filldir)
                                           rdir->tail - rdir->head, &st);
                         if (err) {
                                 p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
-                                err = -EIO;
                                 p9stat_free(&st);
-                                goto unlock_and_exit;
+                                return -EIO;
                         }
                         reclen = st.size+2;
 
@@ -180,19 +153,13 @@ static int v9fs_dir_readdir(struct file *filp, void *dirent, filldir_t filldir)
 
                         p9stat_free(&st);
 
-                        if (over) {
-                                err = 0;
-                                goto unlock_and_exit;
-                        }
+                        if (over)
+                                return 0;
+
                         rdir->head += reclen;
                         filp->f_pos += reclen;
                 }
         }
-
-unlock_and_exit:
-        mutex_unlock(&rdir->mutex);
-exit:
-        return err;
 }
 
 /**
@@ -218,21 +185,16 @@ static int v9fs_dir_readdir_dotl(struct file *filp, void *dirent,
 
         buflen = fid->clnt->msize - P9_READDIRHDRSZ;
 
-        err = v9fs_alloc_rdir_buf(filp, buflen);
-        if (err)
-                goto exit;
-        rdir = (struct p9_rdir *) fid->rdir;
+        rdir = v9fs_alloc_rdir_buf(filp, buflen);
+        if (!rdir)
+                return -ENOMEM;
 
-        err = mutex_lock_interruptible(&rdir->mutex);
-        if (err)
-                return err;
-
-        while (err == 0) {
+        while (1) {
                 if (rdir->tail == rdir->head) {
                         err = p9_client_readdir(fid, rdir->buf, buflen,
                                                 filp->f_pos);
                         if (err <= 0)
-                                goto unlock_and_exit;
+                                return err;
 
                         rdir->head = 0;
                         rdir->tail = err;
@@ -245,8 +207,7 @@ static int v9fs_dir_readdir_dotl(struct file *filp, void *dirent,
                                             &curdirent);
                         if (err < 0) {
                                 p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
-                                err = -EIO;
-                                goto unlock_and_exit;
+                                return -EIO;
                         }
 
                         /* d_off in dirent structure tracks the offset into
@@ -261,20 +222,13 @@ static int v9fs_dir_readdir_dotl(struct file *filp, void *dirent,
                                         curdirent.d_type);
                         oldoffset = curdirent.d_off;
 
-                        if (over) {
-                                err = 0;
-                                goto unlock_and_exit;
-                        }
+                        if (over)
+                                return 0;
 
                         filp->f_pos = curdirent.d_off;
                         rdir->head += err;
                 }
         }
-
-unlock_and_exit:
-        mutex_unlock(&rdir->mutex);
-exit:
-        return err;
 }