ACPI: OSL: only free map once in osl.c

acpi_os_map_cleanup checks map->refcount outside of acpi_ioremap_lock
before freeing the map. This creates a race condition the can result
in the map being freed more than once.
A panic can be caused by running

for ((i=0; i<10; i++))
do
        for ((j=0; j<100000; j++))
        do
                cat /sys/firmware/acpi/tables/data/BERT >/dev/null
        done &
done

This patch makes sure that only the process that drops the reference
to 0 does the freeing.

Fixes: b7c1fadd6c2e ("ACPI: Do not use krefs under a mutex in osl.c")
Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index a2e844a8e9edb0565abab6357997e2f5cc0e14bf..41168c027a5a444d2be4b3a47f847d211c4af04d 100644 (file)
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -374,19 +374,21 @@ void *__ref acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
 }
 EXPORT_SYMBOL_GPL(acpi_os_map_memory);
 
-static void acpi_os_drop_map_ref(struct acpi_ioremap *map)
+/* Must be called with mutex_lock(&acpi_ioremap_lock) */
+static unsigned long acpi_os_drop_map_ref(struct acpi_ioremap *map)
 {
-       if (!--map->refcount)
+       unsigned long refcount = --map->refcount;
+
+       if (!refcount)
                list_del_rcu(&map->list);
+       return refcount;
 }
 
 static void acpi_os_map_cleanup(struct acpi_ioremap *map)
 {
-       if (!map->refcount) {
-               synchronize_rcu_expedited();
-               acpi_unmap(map->phys, map->virt);
-               kfree(map);
-       }
+       synchronize_rcu_expedited();
+       acpi_unmap(map->phys, map->virt);
+       kfree(map);
 }
 
 /**
@@ -406,6 +408,7 @@ static void acpi_os_map_cleanup(struct acpi_ioremap *map)
 void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
 {
        struct acpi_ioremap *map;
+       unsigned long refcount;
 
        if (!acpi_permanent_mmap) {
                __acpi_unmap_table(virt, size);
@@ -419,10 +422,11 @@ void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
                WARN(true, PREFIX "%s: bad address %p\n", __func__, virt);
                return;
        }
-       acpi_os_drop_map_ref(map);
+       refcount = acpi_os_drop_map_ref(map);
        mutex_unlock(&acpi_ioremap_lock);
 
-       acpi_os_map_cleanup(map);
+       if (!refcount)
+               acpi_os_map_cleanup(map);
 }
 EXPORT_SYMBOL_GPL(acpi_os_unmap_iomem);
 
@@ -457,6 +461,7 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
 {
        u64 addr;
        struct acpi_ioremap *map;
+       unsigned long refcount;
 
        if (gas->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY)
                return;
@@ -472,10 +477,11 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
                mutex_unlock(&acpi_ioremap_lock);
                return;
        }
-       acpi_os_drop_map_ref(map);
+       refcount = acpi_os_drop_map_ref(map);
        mutex_unlock(&acpi_ioremap_lock);
 
-       acpi_os_map_cleanup(map);
+       if (!refcount)
+               acpi_os_map_cleanup(map);
 }
 EXPORT_SYMBOL(acpi_os_unmap_generic_address);