[PATCH RFC tip/core/rcu 5/9] locking/percpu-rwsem: Make percpu_free_rwsem() after kzalloc() safe

From: Paul E. McKenney
Date: Fri Aug 28 2015 - 23:45:33 EST

From: Oleg Nesterov <oleg@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
kernel/locking/percpu-rwsem.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 652a8ee8efe9..67a758df1d7c 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -25,6 +25,13 @@ int __percpu_init_rwsem(struct percpu_rw_semaphore *brw,

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;
brw->fast_read_ctr = NULL; /* catch use after free bugs */

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