Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753624AbaKHJr2 (ORCPT ); Sat, 8 Nov 2014 04:47:28 -0500 Received: from mail-la0-f51.google.com ([209.85.215.51]:58746 "EHLO mail-la0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753486AbaKHJrY (ORCPT ); Sat, 8 Nov 2014 04:47:24 -0500 Subject: [PATCH] ACPI/osl: speedup grace period in acpi_os_map_cleanup From: Konstantin Khlebnikov To: linux-acpi@vger.kernel.org, "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, Len Brown Cc: Tom Boshoven , "Paul E. McKenney" , x86@kernel.org, Josh Triplett , Alexander Monakov Date: Sat, 08 Nov 2014 12:47:17 +0400 Message-ID: <20141108094717.9388.34638.stgit@zurg> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Reported-and-tested-by: Alexander Monakov Tested-by: Tom Boshoven 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; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/