linux-kernel - [PATCH v2 5/8] percpu-rwsem: make percpu_free

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Date:	Fri, 21 Aug 2015 19:42:55 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 5/8] 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 VFS tree.

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

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/locking/percpu-rwsem.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index f325672..3bb2dc9 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;
+
 	free_percpu(brw->fast_read_ctr);
 	brw->fast_read_ctr = NULL; /* catch use after free bugs */
 }
-- 
1.5.5.1

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