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Groups > linux.kernel > #1215676

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

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From: Oleg Nesterov <oleg@redhat.com>

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>
---
 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;
+
 	free_percpu(brw->fast_read_ctr);
 	brw->fast_read_ctr = NULL; /* catch use after free bugs */
 }
-- 
1.8.1.5

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[PATCH RFC tip/core/rcu 1/9] rcu: Create rcu_sync infrastructure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 6/9] locking/percpu-rwsem: Make use of the rcu_sync infrastructure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 2/9] rcu_sync: Simplify rcu_sync using new rcu_sync_ops structure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 5/9] locking/percpu-rwsem: Make percpu_free_rwsem() after kzalloc() safe "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 7/9] locking/percpu-rwsem: Fix the comments outdated by rcu_sync "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 8/9] locking/percpu-rwsem: Clean up the lockdep annotations in percpu_down_read() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200
  [PATCH RFC tip/core/rcu 3/9] rcu_sync: Add CONFIG_PROVE_RCU checks "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-29 05:50 +0200

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