locking/percpu-rwsem: Make percpu_free_rwsem() after kzalloc() safe

This is the temporary ugly hack which will be reverted later. We only
need it to ensure that the next patch will not break "change sb_writers
to use percpu_rw_semaphore" patches routed via the VFS tree.

The alloc_super()->destroy_super() error path assumes that it is safe
to call percpu_free_rwsem() after kzalloc() without percpu_init_rwsem(),
so let's not disappoint it.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index e2621fbbcbd16f60db09e09ae614a8a87fda4791..9529a30ec57b44ef46496435c4578907138a8b70 100644 (file)
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -26,6 +26,13 @@ EXPORT_SYMBOL_GPL(__percpu_init_rwsem);
 
 void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
 {
+       /*
+        * XXX: temporary kludge. The error path in alloc_super()
+        * assumes that percpu_free_rwsem() is safe after kzalloc().
+        */
+       if (!brw->fast_read_ctr)
+               return;
+
        free_percpu(brw->fast_read_ctr);
        brw->fast_read_ctr = NULL; /* catch use after free bugs */
 }