The open-coded mutex implementation for ARMv6+ cores suffers from a
severe lack of barriers, so in the uncontended case we don't actually
protect any accesses performed during the critical section.

Furthermore, the code is largely a duplication of the ARMv6+ atomic_dec
code but optimised to remove a branch instruction, as the mutex fastpath
was previously inlined. Now that this is executed out-of-line, we can
reuse the atomic access code for the locking (in fact, we use the xchg
code as this produces shorter critical sections).

This patch uses the generic xchg based implementation for mutexes on
ARMv6+, which introduces barriers to the lock/unlock operations and also
has the benefit of removing a fair amount of inline assembly code.

Cc: <stable@vger.kernel.org>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NNicolas Pitre <nico@linaro.org>
Reported-by: NShan Kang <kangshan0910@gmail.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Move platform independent header files to arch/arm/include/asm, leaving
those in asm/arch* and asm/plat* alone.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Signed-off-by: NHarvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch from Nicolas Pitre

Since:

	if (unlikely(__res || __ex_flag))

produces worse code on ARM than:

	if (unlikely(__res | __ex_flag))

I therefore made it more explicit:

	__res |= __ex_flag;
	if (unlikely(__res != 0))

so it is not seen as a typo again.

Also made everything static inline rather than macros for better readability
(both produce the same code after all).

And finally added missing \t from multi-line assembly code.
Signed-off-by: NNicolas Pitre <nico@cam.org>
Acked-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

add the ARM version of mutex.h, which is optimized in assembly for
ARMv6, and uses the xchg implementation on pre-ARMv6.
Signed-off-by: NIngo Molnar <mingo@elte.hu>