linux-kernel - [PATCH 3.12 069/176] ACPI / osl: speedup grace period in acpi_os_map

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Message-Id: <b3959c772ebaf1efedb44085c5bc43129704274b.1422455352.git.jslaby@suse.cz>
Date:	Wed, 28 Jan 2015 15:28:19 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Konstantin Khlebnikov <koct9i@...il.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 069/176] ACPI / osl: speedup grace period in acpi_os_map_cleanup

From: Konstantin Khlebnikov <koct9i@...il.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 74b51ee152b6d99e61ba329799a039453fb9438f upstream.

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 synchronize_rcu_expedited()
which is much faster.

Link: https://devtalk.nvidia.com/default/topic/567297/linux/linux-3-10-driver-crash/
Signed-off-by: Konstantin Khlebnikov <koct9i@...il.com>
Reported-and-tested-by: Alexander Monakov <amonakov@...il.com>
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/acpi/osl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index e5f416c7f66e..d73f85247272 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -421,7 +421,7 @@ 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();
+		synchronize_rcu_expedited();
 		acpi_unmap(map->phys, map->virt);
 		kfree(map);
 	}
-- 
2.2.2

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