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From:   Davidlohr Bueso <dave@stgolabs.net>
To:     eric@anholt.net, wahrenst@gmx.net
Cc:     gregkh@linuxfoundation.org, dave@stgolabs.net,
        linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org
Subject: [PATCH resend] staging: vc04_services: replace g_free_fragments_mutex with spinlock
Date:   Fri,  1 Nov 2019 11:29:49 -0700
Message-Id: <20191101182949.21225-1-dave@stgolabs.net>
In-Reply-To: <20191028165909.GA469472@kroah.com>
References: <20191028165909.GA469472@kroah.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

There is no need to be using a semaphore, or a sleeping lock
in the first place: critical region is extremely short, does not
call into any blocking calls and furthermore lock and unlocking
operations occur in the same context.

Get rid of another semaphore user by replacing it with a spinlock.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
---
This is in an effort to further reduce semaphore users in the kernel.

This is a resend, which just seems simpler given the confusions.

 .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
index 8dc730cfe7a6..710d21654128 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
@@ -63,7 +63,7 @@ static char *g_free_fragments;
 static struct semaphore g_free_fragments_sema;
 static struct device *g_dev;
 
-static DEFINE_SEMAPHORE(g_free_fragments_mutex);
+static DEFINE_SPINLOCK(g_free_fragments_lock);
 
 static irqreturn_t
 vchiq_doorbell_irq(int irq, void *dev_id);
@@ -528,11 +528,11 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
 
 		WARN_ON(g_free_fragments == NULL);
 
-		down(&g_free_fragments_mutex);
+		spin_lock(&g_free_fragments_lock);
 		fragments = g_free_fragments;
 		WARN_ON(fragments == NULL);
 		g_free_fragments = *(char **) g_free_fragments;
-		up(&g_free_fragments_mutex);
+		spin_unlock(&g_free_fragments_lock);
 		pagelist->type = PAGELIST_READ_WITH_FRAGMENTS +
 			(fragments - g_fragments_base) / g_fragments_size;
 	}
@@ -591,10 +591,10 @@ free_pagelist(struct vchiq_pagelist_info *pagelistinfo,
 			kunmap(pages[num_pages - 1]);
 		}
 
-		down(&g_free_fragments_mutex);
+		spin_lock(&g_free_fragments_lock);
 		*(char **)fragments = g_free_fragments;
 		g_free_fragments = fragments;
-		up(&g_free_fragments_mutex);
+		spin_unlock(&g_free_fragments_lock);
 		up(&g_free_fragments_sema);
 	}
 
-- 
2.16.4