From: Konstantin Khlebnikov Date: Sun, 9 Nov 2014 09:53:37 +0000 (+0400) Subject: ACPI / osl: speedup grace period in acpi_os_map_cleanup X-Git-Tag: omap-for-v3.19/fixes-rc1~136^2~8^3~1 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=74b51ee152b6d99e61ba329799a039453fb9438f;p=pandora-kernel.git ACPI / osl: speedup grace period in acpi_os_map_cleanup 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 Reported-and-tested-by: Alexander Monakov Reviewed-by: Paul E. McKenney Signed-off-by: Rafael J. Wysocki --- Reading git-diff-tree failed