ARM: 6975/1: pmu: reject duplicate PMU registrations

Currently, the PMU reservation framework allows for multiple PMUs of
the same type to register themselves. This can lead to a bug with the
sequence:

register_pmu(pmu1);
reserve_pmu(pmu_type);
register_pmu(pmu2);
release_pmu(pmu1);

Here, pmu1 cannot be released, and pmu2 cannot be reserved.

This patch modifies register_pmu to reject registrations where a PMU is
already present, preventing this problem. PMUs which can have multiple
instances should not use the PMU reservation framework.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 6 insertions, 6 deletions

diff --git a/arch/arm/kernel/pmu.c b/arch/arm/kernel/pmu.c
index 87942b931c6..de6b1b0860c 100644
--- a/arch/arm/kernel/pmu.c
+++ b/arch/arm/kernel/pmu.c
@@ -34,13 +34,13 @@ static int __devinit pmu_register(struct platform_device *pdev,
                 return -EINVAL;
         }
 
-        if (pmu_devices[type])
-                pr_warning("registering new PMU device type %d overwrites "
-                                "previous registration!\n", type);
-        else
-                pr_info("registered new PMU device of type %d\n",
-                                type);
+        if (pmu_devices[type]) {
+                pr_warning("rejecting duplicate registration of PMU device "
+                        "type %d.", type);
+                return -ENOSPC;
+        }
 
+        pr_info("registered new PMU device of type %d\n", type);
         pmu_devices[type] = pdev;
         return 0;
 }