SUNRPC: move cache_detail->cache_request callback call to cache_read()

The reason to move cache_request() callback call from
sunrpc_cache_pipe_upcall() to cache_read() is that this garantees, that cache
access will be done userspace process context (only userspace process have
proper root context).
This is required for NFSd support in container: svc_export_request() (which is
cache_request callback) calls d_path(), which, in turn, traverse dentry up to
current->fs->root. Kernel threads always have global root, while container
have be in "root jail" - i.e. have it's own nested root.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 20 insertions, 12 deletions

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 8ffec5aebeff..55024714f001 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -750,6 +750,18 @@ struct cache_reader {
         int                     offset; /* if non-0, we have a refcnt on next request */
 };
 
+static int cache_request(struct cache_detail *detail,
+                               struct cache_request *crq)
+{
+        char *bp = crq->buf;
+        int len = PAGE_SIZE;
+
+        detail->cache_request(detail, crq->item, &bp, &len);
+        if (len < 0)
+                return -EAGAIN;
+        return PAGE_SIZE - len;
+}
+
 static ssize_t cache_read(struct file *filp, char __user *buf, size_t count,
                           loff_t *ppos, struct cache_detail *cd)
 {
@@ -784,6 +796,13 @@ static ssize_t cache_read(struct file *filp, char __user *buf, size_t count,
                 rq->readers++;
         spin_unlock(&queue_lock);
 
+        if (rq->len == 0) {
+                err = cache_request(cd, rq);
+                if (err < 0)
+                        goto out;
+                rq->len = err;
+        }
+
         if (rp->offset == 0 && !test_bit(CACHE_PENDING, &rq->item->flags)) {
                 err = -EAGAIN;
                 spin_lock(&queue_lock);
@@ -1145,8 +1164,6 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
 
         char *buf;
         struct cache_request *crq;
-        char *bp;
-        int len;
 
         if (!detail->cache_request)
                 return -EINVAL;
@@ -1166,19 +1183,10 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
                 return -EAGAIN;
         }
 
-        bp = buf; len = PAGE_SIZE;
-
-        detail->cache_request(detail, h, &bp, &len);
-
-        if (len < 0) {
-                kfree(buf);
-                kfree(crq);
-                return -EAGAIN;
-        }
         crq->q.reader = 0;
         crq->item = cache_get(h);
         crq->buf = buf;
-        crq->len = PAGE_SIZE - len;
+        crq->len = 0;
         crq->readers = 0;
         spin_lock(&queue_lock);
         list_add_tail(&crq->q.list, &detail->queue);