Commit 1b79e551 authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
Browse files

[PATCH] add probe_kernel_address() 



Add a version of __get_user() which is safe to call inside mmap_sem.

Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent aafe6c2a

include/linux/uaccess.h

+22 −0
Original line number Diff line number Diff line
@@ -19,4 +19,26 @@ static inline unsigned long __copy_from_user_nocache(void *to, 


#endif		/* ARCH_HAS_NOCACHE_UACCESS */



/**

 * probe_kernel_address(): safely attempt to read from a location

 * @addr: address to read from - its type is type typeof(retval)*

 * @retval: read into this variable

 *

 * Safely read from address @addr into variable @revtal.  If a kernel fault

 * happens, handle that and return -EFAULT.

 * We ensure that the __get_user() is executed in atomic context so that

 * do_page_fault() doesn't attempt to take mmap_sem.  This makes

 * probe_kernel_address() suitable for use within regions where the caller

 * already holds mmap_sem, or other locks which nest inside mmap_sem.

 */

#define probe_kernel_address(addr, retval)		\

	({						\

		long ret;				\

							\

		inc_preempt_count();			\

		ret = __get_user(retval, addr);		\

		dec_preempt_count();			\

		ret;					\

	})



#endif		/* __LINUX_UACCESS_H__ */