linux-kernel - [PATCH] locking/pvqspinlock: restore/set vcpu_hashed state after failing adaptive locking spinning

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 14 Jul 2016 15:53:46 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Wanpeng Li <wanpeng.li@...mail.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Waiman Long <Waiman.Long@....com>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: [PATCH] locking/pvqspinlock: restore/set vcpu_hashed state after failing adaptive locking spinning

From: Wanpeng Li <wanpeng.li@...mail.com>

When the lock holder vCPU is racing with the queue head:

   CPU 0 (lock holder)    CPU1 (queue head)
   ===================    =================
   spin_lock();           spin_lock();
    pv_kick_node();        pv_wait_head_or_lock();
                            if (!lp) {
                             lp = pv_hash(lock, pn);
							 xchg(&l->locked, _Q_SLOW_VAL);
							}
						    WRITE_ONCE(pn->state, vcpu_halted);
     cmpxchg(&pn->state, 
      vcpu_halted, vcpu_hashed);
     WRITE_ONCE(l->locked, _Q_SLOW_VAL);
     (void)pv_hash(lock, pn);

In this case, lock holder inserts the pv_node of queue head into the 
hash table and set _Q_SLOW_VAL unnecessary. This patch avoids it by 
restoring/setting vcpu_halted state after failing adaptive locking 
spinning.

Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Waiman Long <Waiman.Long@....com>
Cc: Davidlohr Bueso <dave@...olabs.net>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 kernel/locking/qspinlock_paravirt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 21ede57..ac7d20b 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -450,7 +450,7 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
 				goto gotlock;
 			}
 		}
-		WRITE_ONCE(pn->state, vcpu_halted);
+		WRITE_ONCE(pn->state, vcpu_hashed);
 		qstat_inc(qstat_pv_wait_head, true);
 		qstat_inc(qstat_pv_wait_again, waitcnt);
 		pv_wait(&l->locked, _Q_SLOW_VAL);
-- 
1.9.1