linux-kernel - [PATCH 4.2.y-ckt 85/93] s390/spinlock: avoid yield to non existent cpu

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Date:	Tue, 26 Apr 2016 11:17:25 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 85/93] s390/spinlock: avoid yield to non existent cpu

4.2.8-ckt9 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Heiko Carstens <heiko.carstens@...ibm.com>

commit 8497695243f70fd19ed6cf28b63584f1b608b5f9 upstream.

arch_spin_lock_wait_flags() checks if a spinlock is not held before
trying a compare and swap instruction. If the lock is unlocked it
tries the compare and swap instruction, however if a different cpu
grabbed the lock in the meantime the instruction will fail as
expected.

Subsequently the arch_spin_lock_wait_flags() incorrectly tries to
figure out if the cpu that holds the lock is running. However it is
using the wrong cpu number for this (-1) and then will also yield the
current cpu to the wrong cpu.

Fix this by adding a missing continue statement.

Fixes: 470ada6b1a1d ("s390/spinlock: refactor arch_spin_lock_wait[_flags]")
Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 arch/s390/lib/spinlock.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index d6c9991..27f2651 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -90,6 +90,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
 			if (_raw_compare_and_swap(&lp->lock, 0, cpu))
 				return;
 			local_irq_restore(flags);
+			continue;
 		}
 		/* Check if the lock owner is running. */
 		if (!smp_vcpu_scheduled(~owner)) {
-- 
2.7.4