[PATCH linux dev-4.13 10/16] hwmon (p9_sbe): Convert client_lock from a spinlock to a mutex

[Andrew Jeffery]

The hwmon occ implementation allocates GFP_KERNEL memory in occ_open_common(),
therefore we cannot call it under a spinlock as it may sleep. Compiling with
lock debugging enabled gives us the following warning:

[    4.420000] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2879 lockdep_trace_alloc+0xf0/0x124
[    4.420000] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
[    4.420000] CPU: 0 PID: 1 Comm: swapper Not tainted 4.10.17-00526-g1cbacc6bd3a1 #2334
[    4.420000] Hardware name: ASpeed SoC
[    4.420000] [<80010eec>] (unwind_backtrace) from [<8000e664>] (show_stack+0x20/0x24)
[    4.420000] [<8000e664>] (show_stack) from [<80249160>] (dump_stack+0x20/0x28)
[    4.420000] [<80249160>] (dump_stack) from [<8001d3a0>] (__warn+0xe0/0x108)
[    4.420000] [<8001d3a0>] (__warn) from [<8001d40c>] (warn_slowpath_fmt+0x44/0x4c)
[    4.420000] [<8001d40c>] (warn_slowpath_fmt) from [<8005d2cc>] (lockdep_trace_alloc+0xf0/0x124)
[    4.420000] [<8005d2cc>] (lockdep_trace_alloc) from [<8012bb1c>] (kmem_cache_alloc_trace+0x3c/0x284)
[    4.420000] [<8012bb1c>] (kmem_cache_alloc_trace) from [<8034fa2c>] (occ_open_common+0x30/0xac)
[    4.420000] [<8034fa2c>] (occ_open_common) from [<80350bac>] (occ_drv_open+0x24/0x28)
[    4.420000] [<80350bac>] (occ_drv_open) from [<803638fc>] (p9_sbe_occ_send_cmd+0x44/0x13c)
[    4.420000] [<803638fc>] (p9_sbe_occ_send_cmd) from [<803615b8>] (occ_poll+0x6c/0x1c0)
[    4.420000] [<803615b8>] (occ_poll) from [<80363a84>] (p9_sbe_occ_probe+0x90/0x178)
[    4.420000] [<80363a84>] (p9_sbe_occ_probe) from [<802b9850>] (platform_drv_probe+0x60/0xbc)
[    4.420000] [<802b9850>] (platform_drv_probe) from [<802b76b0>] (driver_probe_device+0x114/0x430)
[    4.420000] [<802b76b0>] (driver_probe_device) from [<802b7a98>] (__driver_attach+0xcc/0x10c)
[    4.420000] [<802b7a98>] (__driver_attach) from [<802b5770>] (bus_for_each_dev+0x5c/0xac)
[    4.420000] [<802b5770>] (bus_for_each_dev) from [<802b7c74>] (driver_attach+0x28/0x30)
[    4.420000] [<802b7c74>] (driver_attach) from [<802b6268>] (bus_add_driver+0x19c/0x25c)
[    4.420000] [<802b6268>] (bus_add_driver) from [<802b8abc>] (driver_register+0x88/0x104)
[    4.420000] [<802b8abc>] (driver_register) from [<802ba468>] (__platform_driver_register+0x3c/0x50)
[    4.420000] [<802ba468>] (__platform_driver_register) from [<8066d804>] (p9_sbe_occ_driver_init+0x18/0x20)
[    4.420000] [<8066d804>] (p9_sbe_occ_driver_init) from [<8064ae7c>] (do_one_initcall+0xa8/0x168)
[    4.420000] [<8064ae7c>] (do_one_initcall) from [<8064b04c>] (kernel_init_freeable+0x110/0x1c8)
[    4.420000] [<8064b04c>] (kernel_init_freeable) from [<804a9034>] (kernel_init+0x18/0x104)
[    4.420000] [<804a9034>] (kernel_init) from [<8000a888>] (ret_from_fork+0x14/0x2c)

Avoid the warning (or the need for GFP_ATOMIC) and allow for reduced system
latency by using a mutex instead. Mutual exclusion is the only requirement, we
do not need to block pre-emption.

Signed-off-by: Andrew Jeffery <andrew at aj.id.au>
---
 drivers/hwmon/occ/p9_sbe.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/hwmon/occ/p9_sbe.c b/drivers/hwmon/occ/p9_sbe.c
index 51bdfa89f1a6..38cf57ad1bb8 100644
--- a/drivers/hwmon/occ/p9_sbe.c
+++ b/drivers/hwmon/occ/p9_sbe.c
@@ -34,34 +34,32 @@ struct p9_sbe_occ {
 	 * open, close and NULL assignment. This prevents simultaneous opening
 	 * and closing of the client, or closing multiple times.
 	 */
-	spinlock_t client_lock;
+	struct mutex client_lock;
 };
 
 #define to_p9_sbe_occ(x)	container_of((x), struct p9_sbe_occ, occ)
 
 static void p9_sbe_occ_close_client(struct p9_sbe_occ *ctx)
 {
-	unsigned long flags;
 	struct occ_client *tmp_client;
 
-	spin_lock_irqsave(&ctx->client_lock, flags);
+	mutex_lock(&ctx->client_lock);
 	tmp_client = ctx->client;
 	ctx->client = NULL;
 	occ_drv_release(tmp_client);
-	spin_unlock_irqrestore(&ctx->client_lock, flags);
+	mutex_unlock(&ctx->client_lock);
 }
 
 static int p9_sbe_occ_send_cmd(struct occ *occ, u8 *cmd)
 {
 	int rc;
-	unsigned long flags;
 	struct occ_response *resp = &occ->resp;
 	struct p9_sbe_occ *ctx = to_p9_sbe_occ(occ);
 
-	spin_lock_irqsave(&ctx->client_lock, flags);
+	mutex_lock(&ctx->client_lock);
 	if (ctx->sbe)
 		ctx->client = occ_drv_open(ctx->sbe, 0);
-	spin_unlock_irqrestore(&ctx->client_lock, flags);
+	mutex_unlock(&ctx->client_lock);
 
 	if (!ctx->client)
 		return -ENODEV;
@@ -115,7 +113,7 @@ static int p9_sbe_occ_probe(struct platform_device *pdev)
 	if (!ctx)
 		return -ENOMEM;
 
-	spin_lock_init(&ctx->lock);
+	mutex_init(&ctx->client_lock);
 	ctx->sbe = pdev->dev.parent;
 	occ = &ctx->occ;
 	occ->bus_dev = &pdev->dev;
-- 
2.14.1