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Groups > linux.kernel > #1240720

[PATCH tip/core/rcu 09/13] 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 e2621fbbcbd1..9529a30ec57b 100644
--- 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 */
 }
-- 
2.5.2

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Thread

[PATCH tip/core/rcu 0/13] percpu-rwsem patches for 4.4 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
  [PATCH tip/core/rcu 02/13] locking/percpu-rwsem: Export symbols for locktorture "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
  [PATCH tip/core/rcu 07/13] rcu_sync: Add CONFIG_PROVE_RCU checks "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
  [PATCH tip/core/rcu 05/13] rcu: Create rcu_sync infrastructure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
  [PATCH tip/core/rcu 01/13] locktorture: Support rtmutex torturing "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
    [PATCH tip/core/rcu 09/13] locking/percpu-rwsem: Make percpu_free_rwsem() after kzalloc() safe "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
    [PATCH tip/core/rcu 04/13] torture: Consolidate cond_resched_rcu_qs() into stutter_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
    [PATCH tip/core/rcu 12/13] locking/percpu-rwsem: Clean up the lockdep annotations in percpu_down_read() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
    [PATCH tip/core/rcu 08/13] rcu_sync: Introduce rcu_sync_dtor() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
    [PATCH tip/core/rcu 06/13] rcu_sync: Simplify rcu_sync using new rcu_sync_ops structure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
    [PATCH tip/core/rcu 11/13] locking/percpu-rwsem: Fix the comments outdated by rcu_sync "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:50 +0200
    [PATCH tip/core/rcu 13/13] rcu_sync: Cleanup the CONFIG_PROVE_RCU checks "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 19:00 +0200
    [PATCH tip/core/rcu 03/13] locktorture: Add torture tests for percpu_rwsem "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 19:00 +0200
    [PATCH tip/core/rcu 10/13] locking/percpu-rwsem: Make use of the rcu_sync infrastructure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 19:00 +0200
  Re: [PATCH tip/core/rcu 0/13] percpu-rwsem patches for 4.4 Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:50 +0200
    Re: [PATCH tip/core/rcu 0/13] percpu-rwsem patches for 4.4 Oleg Nesterov <oleg@redhat.com> - 2015-10-06 21:00 +0200
      Re: [PATCH tip/core/rcu 0/13] percpu-rwsem patches for 4.4 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 21:40 +0200
        Re: [PATCH tip/core/rcu 0/13] percpu-rwsem patches for 4.4 Josh Triplett <josh@joshtriplett.org> - 2015-10-06 22:40 +0200

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