[PATCH] PM / clock_ops: Fix crash in clocks management code if !CONFIG_PM_RUNTIME

[Geert Uytterhoeven <geert+renesas@glider.be>]

Unlike the clocks management code for runtime PM, the code used for
system suspend does not check the pm_clock_entry.status field.
If pm_clk_acquire() failed, ce->status will be PCE_STATUS_ERROR, and
ce->clk will be a negative error code (e.g. 0xfffffffe = -2 = -ENOENT).

Depending on the clock implementation, suspend or resume may crash with:

    Unable to handle kernel NULL pointer dereference at virtual address 00000026

(CCF clk_disable() has an IS_ERR_OR_NULL() check, while CCF clk_enable()
 only has a NULL check; pre-CCF implementations may behave differently)

While just checking for PCE_STATUS_ERROR would be sufficient, it doesn't
hurt to use the same state machine as is done for runtime PM, as this
makes the two versions more similar, and eligible for a future
consolidation.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
This crash started to happen on armadillo-legacy during s2ram if
CONFIG_PM_RUNTIME is not set after applying "[PATCH v2 07/11] ARM:
shmobile: r8a7740/armadillo legacy: Add A4MP pm domain support"
(http://www.spinics.net/linux/lists/arm-kernel/msg365438.html), as
there's no NULL clock for the HDMI device.

Most existing code calling pm_clk_suspend()/pm_clk_resume() is protected
by a check for CONFIG_PM_RUNTIME (davinci, keystone, omap1,
drivers/sh/pm_runtime.c), so it was not affected by this bug.

Exceptions are:
  - arch/arm/mach-shmobile/pm-r8a7779.c (marzen),
  - arch/arm/mach-shmobile/pm-rmobile.c (r8a7740/armadillo and
    sh7372/mackerel),
but it's difficult to assess from the code whether the bug is really
triggered on these platforms.

Grygorii Strashko's "[PATCH v1 2/4] ARM: keystone: pm: switch to use
generic pm domains" is not affected, as pm_clk_add_clk() is only called
for existing clocks.

If it crashes on marzen or mackerel, I think this fix needs to be
applied to stable, too. I don't have access to marzen or mackerel boards,
though.

How to test:
  - Build a kernel with CONFIG_PM_SLEEP/CONFIG_SUSPEND enabled, but
    CONFIG_PM_RUNTIME disabled,
  - echo 0 > /sys/module/printk/parameters/console_suspend,
  - echo mem > /sys/power/state,
  - wake up using e.g. gpio-keys or serial console activity.
---
 drivers/base/power/clock_ops.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/base/power/clock_ops.c b/drivers/base/power/clock_ops.c
index b99e6c06ee678ecb..78369305e0698109 100644
--- a/drivers/base/power/clock_ops.c
+++ b/drivers/base/power/clock_ops.c
@@ -368,8 +368,13 @@ int pm_clk_suspend(struct device *dev)
 
 	spin_lock_irqsave(&psd->lock, flags);
 
-	list_for_each_entry_reverse(ce, &psd->clock_list, node)
-		clk_disable(ce->clk);
+	list_for_each_entry_reverse(ce, &psd->clock_list, node) {
+		if (ce->status < PCE_STATUS_ERROR) {
+			if (ce->status = PCE_STATUS_ENABLED)
+				clk_disable(ce->clk);
+			ce->status = PCE_STATUS_ACQUIRED;
+		}
+	}
 
 	spin_unlock_irqrestore(&psd->lock, flags);
 
@@ -385,6 +390,7 @@ int pm_clk_resume(struct device *dev)
 	struct pm_subsys_data *psd = dev_to_psd(dev);
 	struct pm_clock_entry *ce;
 	unsigned long flags;
+	int ret;
 
 	dev_dbg(dev, "%s()\n", __func__);
 
@@ -394,8 +400,13 @@ int pm_clk_resume(struct device *dev)
 
 	spin_lock_irqsave(&psd->lock, flags);
 
-	list_for_each_entry(ce, &psd->clock_list, node)
-		__pm_clk_enable(dev, ce->clk);
+	list_for_each_entry(ce, &psd->clock_list, node) {
+		if (ce->status < PCE_STATUS_ERROR) {
+			ret = __pm_clk_enable(dev, ce->clk);
+			if (!ret)
+				ce->status = PCE_STATUS_ENABLED;
+		}
+	}
 
 	spin_unlock_irqrestore(&psd->lock, flags);
 
-- 
1.9.1