Re: [PATCH 1/4] bitops: Introduce assign_bit()

[Bart Van Assche <Bart.VanAssche@wdc.com>]

On Wed, 2017-08-23 at 09:32 +0200, Linus Walleij wrote:
> Can someone explain when I use the bitop_foo() and when I
> use the __bitop_foo(). I am asking so I can understand patch
> 2/4 in this series.

That's easy. From Documentation/core-api/atomic_ops.rst:

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Finally, there are non-atomic versions of the bitmask operations
provided.  They are used in contexts where some other higher-level SMP
locking scheme is being used to protect the bitmask, and thus less
expensive non-atomic operations may be used in the implementation.
They have names similar to the above bitmask operation interfaces,
except that two underscores are prefixed to the interface name. ::

	void __set_bit(unsigned long nr, volatile unsigned long *addr);
	void __clear_bit(unsigned long nr, volatile unsigned long *addr);
	void __change_bit(unsigned long nr, volatile unsigned long *addr);
	int __test_and_set_bit(unsigned long nr, volatile unsigned long *addr);
	int __test_and_clear_bit(unsigned long nr, volatile unsigned long *addr);
	int __test_and_change_bit(unsigned long nr, volatile unsigned long *addr);

These non-atomic variants also do not require any special memory
barrier semantics.
----------------------------------------------------------------------

Bart.