SUNRPC: Fix a potential race in rpc_wake_up_task()

Use RCU to ensure that we can safely call rpc_finish_wakeup after we've
called __rpc_do_wake_up_task. If not, there is a theoretical race, in which
the rpc_task finishes executing, and gets freed first.

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

1 files changed, 16 insertions, 4 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 883dd4a1c157..29d88209199d 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -102,13 +102,19 @@ struct nfs_write_data *nfs_commit_alloc(void)
         return p;
 }
 
-void nfs_commit_free(struct nfs_write_data *p)
+void nfs_commit_rcu_free(struct rcu_head *head)
 {
+        struct nfs_write_data *p = container_of(head, struct nfs_write_data, task.u.tk_rcu);
         if (p && (p->pagevec != &p->page_array[0]))
                 kfree(p->pagevec);
         mempool_free(p, nfs_commit_mempool);
 }
 
+void nfs_commit_free(struct nfs_write_data *wdata)
+{
+        call_rcu_bh(&wdata->task.u.tk_rcu, nfs_commit_rcu_free);
+}
+
 struct nfs_write_data *nfs_writedata_alloc(size_t len)
 {
         unsigned int pagecount = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -131,13 +137,19 @@ struct nfs_write_data *nfs_writedata_alloc(size_t len)
         return p;
 }
 
-static void nfs_writedata_free(struct nfs_write_data *p)
+static void nfs_writedata_rcu_free(struct rcu_head *head)
 {
+        struct nfs_write_data *p = container_of(head, struct nfs_write_data, task.u.tk_rcu);
         if (p && (p->pagevec != &p->page_array[0]))
                 kfree(p->pagevec);
         mempool_free(p, nfs_wdata_mempool);
 }
 
+static void nfs_writedata_free(struct nfs_write_data *wdata)
+{
+        call_rcu_bh(&wdata->task.u.tk_rcu, nfs_writedata_rcu_free);
+}
+
 void nfs_writedata_release(void *wdata)
 {
         nfs_writedata_free(wdata);
@@ -258,7 +270,7 @@ static int nfs_writepage_sync(struct nfs_open_context *ctx, struct inode *inode,
 io_error:
         nfs_end_data_update(inode);
         end_page_writeback(page);
-        nfs_writedata_free(wdata);
+        nfs_writedata_release(wdata);
         return written ? written : result;
 }
 
@@ -1043,7 +1055,7 @@ out_bad:
         while (!list_empty(&list)) {
                 data = list_entry(list.next, struct nfs_write_data, pages);
                 list_del(&data->pages);
-                nfs_writedata_free(data);
+                nfs_writedata_release(data);
         }
         nfs_mark_request_dirty(req);
         nfs_clear_page_writeback(req);