From 4b20db3de8dab005b07c74161cb041db8c5ff3a7 Mon Sep 17 00:00:00 2001 From: Thomas Hellstrom Date: Tue, 6 Nov 2012 11:31:49 +0000 Subject: kref: Implement kref_get_unless_zero v3 This function is intended to simplify locking around refcounting for objects that can be looked up from a lookup structure, and which are removed from that lookup structure in the object destructor. Operations on such objects require at least a read lock around lookup + kref_get, and a write lock around kref_put + remove from lookup structure. Furthermore, RCU implementations become extremely tricky. With a lookup followed by a kref_get_unless_zero *with return value check* locking in the kref_put path can be deferred to the actual removal from the lookup structure and RCU lookups become trivial. v2: Formatting fixes. v3: Invert the return value. Signed-off-by: Thomas Hellstrom Signed-off-by: Dave Airlie --- include/linux/kref.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'include/linux') diff --git a/include/linux/kref.h b/include/linux/kref.h index 65af6887872f..4972e6e9ca93 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -111,4 +111,25 @@ static inline int kref_put_mutex(struct kref *kref, } return 0; } + +/** + * kref_get_unless_zero - Increment refcount for object unless it is zero. + * @kref: object. + * + * Return non-zero if the increment succeeded. Otherwise return 0. + * + * This function is intended to simplify locking around refcounting for + * objects that can be looked up from a lookup structure, and which are + * removed from that lookup structure in the object destructor. + * Operations on such objects require at least a read lock around + * lookup + kref_get, and a write lock around kref_put + remove from lookup + * structure. Furthermore, RCU implementations become extremely tricky. + * With a lookup followed by a kref_get_unless_zero *with return value check* + * locking in the kref_put path can be deferred to the actual removal from + * the lookup structure and RCU lookups become trivial. + */ +static inline int __must_check kref_get_unless_zero(struct kref *kref) +{ + return atomic_add_unless(&kref->refcount, 1, 0); +} #endif /* _KREF_H_ */ -- cgit v1.2.3 From 4b9347dcbe3b426d19bda99b2061a2d1fe5a2dce Mon Sep 17 00:00:00 2001 From: Marek Szyprowski Date: Mon, 15 Oct 2012 16:03:51 +0200 Subject: common: DMA-mapping: add DMA_ATTR_FORCE_CONTIGUOUS attribute This patch adds DMA_ATTR_FORCE_CONTIGUOUS attribute to the DMA-mapping subsystem. By default DMA-mapping subsystem is allowed to assemble the buffer allocated by dma_alloc_attrs() function from individual pages if it can be mapped as contiguous chunk into device dma address space. By specifing this attribute the allocated buffer is forced to be contiguous also in physical memory. Signed-off-by: Marek Szyprowski --- Documentation/DMA-attributes.txt | 9 +++++++++ include/linux/dma-attrs.h | 1 + 2 files changed, 10 insertions(+) (limited to 'include/linux') diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt index f50309081ac7..e59480db9ee0 100644 --- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -91,3 +91,12 @@ transferred to 'device' domain. This attribute can be also used for dma_unmap_{single,page,sg} functions family to force buffer to stay in device domain after releasing a mapping for it. Use this attribute with care! + +DMA_ATTR_FORCE_CONTIGUOUS +------------------------- + +By default DMA-mapping subsystem is allowed to assemble the buffer +allocated by dma_alloc_attrs() function from individual pages if it can +be mapped as contiguous chunk into device dma address space. By +specifing this attribute the allocated buffer is forced to be contiguous +also in physical memory. diff --git a/include/linux/dma-attrs.h b/include/linux/dma-attrs.h index f83f793223ff..c8e1831d7572 100644 --- a/include/linux/dma-attrs.h +++ b/include/linux/dma-attrs.h @@ -17,6 +17,7 @@ enum dma_attr { DMA_ATTR_NON_CONSISTENT, DMA_ATTR_NO_KERNEL_MAPPING, DMA_ATTR_SKIP_CPU_SYNC, + DMA_ATTR_FORCE_CONTIGUOUS, DMA_ATTR_MAX, }; -- cgit v1.2.3