ACPI maintains cache of ioremap regions to speed up operations and
access to them from irq context where ioremap() calls aren't allowed.
This code abuses synchronize_rcu() on unmap path for synchronization
with fast-path in acpi_os_read/write_memory which uses this cache.
Since v3.10 CPUs are allowed to enter idle state even if they have RCU
callbacks queued, see commit c0f4dfd4f90f1667d234d21f15153ea09a2eaa66
("rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks").
That change caused problems with nvidia proprietary driver which calls
acpi_os_map/unmap_generic_address several times during initialization.
Each unmap calls synchronize_rcu and adds significant delay. Totally
initialization is slowed for a couple of seconds and that is enough to
trigger timeout in hardware, gpu decides to "fell off the bus". Widely
spread workaround is reducing "rcu_idle_gp_delay" from 4 to 1 jiffy.
This patch replaces synchronize_rcu with per-acpi_ioremap atomic counter
of side users and wait-queue which signals when counter falls to zero.
List of struct acpi_ioremap is still protected by RCU but they're freed
asynchronously using kfree_rcu.
Signed-off-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Reported-and-tested-by: Alexander Monakov <amonakov@xxxxxxxxx>
Tested-by: Tom Boshoven <tomboshoven@xxxxxxxxx>
Link: https://devtalk.nvidia.com/default/topic/567297/linux/linux-3-10-driver-crash/
---
drivers/acpi/osl.c | 71 ++++++++++++++++++++++++++--------------------------
1 file changed, 36 insertions(+), 35 deletions(-)
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 9964f70..222252a 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -94,10 +94,13 @@ struct acpi_ioremap {
acpi_physical_address phys;
acpi_size size;
unsigned long refcount;
+ atomic_t active;
+ struct rcu_head rcu_head;
};
static LIST_HEAD(acpi_ioremaps);
static DEFINE_MUTEX(acpi_ioremap_lock);
+static DECLARE_WAIT_QUEUE_HEAD(acpi_ioremap_wq);
static void __init acpi_osi_setup_late(void);
@@ -293,17 +296,31 @@ acpi_map_lookup(acpi_physical_address phys, acpi_size size)
return NULL;
}
-/* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
-static void __iomem *
-acpi_map_vaddr_lookup(acpi_physical_address phys, unsigned int size)
+static void __iomem *acpi_get_ioremap(acpi_physical_address phys,
+ acpi_size size, struct acpi_ioremap **pmap)
{
struct acpi_ioremap *map;
+ rcu_read_lock();
map = acpi_map_lookup(phys, size);
- if (map)
+ if (map && atomic_inc_not_zero(&map->active)) {
+ rcu_read_unlock();
+ *pmap = map;
return map->virt + (phys - map->phys);
+ }
+ rcu_read_unlock();
- return NULL;
+ *pmap = NULL;
+ return acpi_os_ioremap(phys, size);
+}
+
+static void acpi_put_ioremap(void __iomem *virt, struct acpi_ioremap *map)
+{
+ if (map) {
+ if (atomic_dec_and_test(&map->active))
+ wake_up_all(&acpi_ioremap_wq);
+ } else
+ iounmap(virt);
}
void __iomem *acpi_os_get_iomem(acpi_physical_address phys, unsigned int size)
@@ -411,6 +428,7 @@ acpi_os_map_iomem(acpi_physical_address phys, acpi_size size)
map->phys = pg_off;
map->size = pg_sz;
map->refcount = 1;
+ atomic_set(&map->active, 1);
list_add_tail_rcu(&map->list, &acpi_ioremaps);
@@ -436,9 +454,10 @@ static void acpi_os_drop_map_ref(struct acpi_ioremap *map)
static void acpi_os_map_cleanup(struct acpi_ioremap *map)
{
if (!map->refcount) {
- synchronize_rcu();
+ atomic_dec(&map->active);
+ wait_event(acpi_ioremap_wq, !atomic_read(&map->active));
acpi_unmap(map->phys, map->virt);
- kfree(map);
+ kfree_rcu(map, rcu_head);
}
}
@@ -947,20 +966,14 @@ static inline u64 read64(const volatile void __iomem *addr)
acpi_status
acpi_os_read_memory(acpi_physical_address phys_addr, u64 *value, u32 width)
{
+ struct acpi_ioremap *map;
void __iomem *virt_addr;
unsigned int size = width / 8;
- bool unmap = false;
u64 dummy;
- rcu_read_lock();
- virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
- if (!virt_addr) {
- rcu_read_unlock();
- virt_addr = acpi_os_ioremap(phys_addr, size);
- if (!virt_addr)
- return AE_BAD_ADDRESS;
- unmap = true;
- }
+ virt_addr = acpi_get_ioremap(phys_addr, size, &map);
+ if (!virt_addr)
+ return AE_BAD_ADDRESS;
if (!value)
value = &dummy;
@@ -982,10 +995,7 @@ acpi_os_read_memory(acpi_physical_address phys_addr, u64 *value, u32 width)
BUG();
}
- if (unmap)
- iounmap(virt_addr);
- else
- rcu_read_unlock();
+ acpi_put_ioremap(virt_addr, map);
return AE_OK;
}
@@ -1006,19 +1016,13 @@ static inline void write64(u64 val, volatile void __iomem *addr)
acpi_status
acpi_os_write_memory(acpi_physical_address phys_addr, u64 value, u32 width)
{
+ struct acpi_ioremap *map;
void __iomem *virt_addr;
unsigned int size = width / 8;
- bool unmap = false;
- rcu_read_lock();
- virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
- if (!virt_addr) {
- rcu_read_unlock();
- virt_addr = acpi_os_ioremap(phys_addr, size);
- if (!virt_addr)
- return AE_BAD_ADDRESS;
- unmap = true;
- }
+ virt_addr = acpi_get_ioremap(phys_addr, size, &map);
+ if (!virt_addr)
+ return AE_BAD_ADDRESS;
switch (width) {
case 8:
@@ -1037,10 +1041,7 @@ acpi_os_write_memory(acpi_physical_address phys_addr, u64 value, u32 width)
BUG();
}
- if (unmap)
- iounmap(virt_addr);
- else
- rcu_read_unlock();
+ acpi_put_ioremap(virt_addr, map);
return AE_OK;
}
--
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