* gregkh@linuxfoundation.org gregkh@linuxfoundation.org:

The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Upstream commit ID 3b885ac1dc35b87a39ee176a6c7e2af9c789d8b8 was tagged to be backported to v4.0+.

It applied cleanly to v4.17 and v4.18. It did not applied to v4.14 and below (to v4.0).

Here is the backport which should apply. Thanks! Helge

diff --git a/arch/parisc/include/asm/spinlock.h b/arch/parisc/include/asm/spinlock.h index e32936cd7f10..7031483b110c 100644 --- a/arch/parisc/include/asm/spinlock.h +++ b/arch/parisc/include/asm/spinlock.h @@ -26,7 +26,6 @@ static inline void arch_spin_lock_flags(arch_spinlock_t *x, { volatile unsigned int *a;

- mb(); a = __ldcw_align(x); while (__ldcw(a) == 0) while (*a == 0) @@ -36,16 +35,15 @@ static inline void arch_spin_lock_flags(arch_spinlock_t *x, local_irq_disable(); } else cpu_relax(); - mb(); }

static inline void arch_spin_unlock(arch_spinlock_t *x) { volatile unsigned int *a; - mb(); + a = __ldcw_align(x); - *a = 1; mb(); + *a = 1; }

static inline int arch_spin_trylock(arch_spinlock_t *x) @@ -53,10 +51,8 @@ static inline int arch_spin_trylock(arch_spinlock_t *x) volatile unsigned int *a; int ret;

- mb(); a = __ldcw_align(x); ret = __ldcw(a) != 0; - mb();

return ret; }

------------------ original commit in Linus's tree ------------------

From 3b885ac1dc35b87a39ee176a6c7e2af9c789d8b8 Mon Sep 17 00:00:00 2001 From: John David Anglin dave.anglin@bell.net Date: Sun, 12 Aug 2018 16:31:17 -0400 Subject: [PATCH] parisc: Remove unnecessary barriers from spinlock.h MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

Now that mb() is an instruction barrier, it will slow performance if we issue unnecessary barriers.

The spinlock defines have a number of unnecessary barriers.  The __ldcw() define is both a hardware and compiler barrier.  The mb() barriers in the routines using __ldcw() serve no purpose.

The only barrier needed is the one in arch_spin_unlock().  We need to ensure all accesses are complete prior to releasing the lock.

Signed-off-by: John David Anglin dave.anglin@bell.net Cc: stable@vger.kernel.org # 4.0+ Signed-off-by: Helge Deller deller@gmx.de