Re: [PATCH] locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN

[Waiman Long]

On 1/15/20 10:16 AM, David Laight wrote:
> From: linux-kernel-owner@xxxxxxxxxxxxxxx <linux-kernel-owner@xxxxxxxxxxxxxxx> On Behalf Of Waiman Long
>> Sent: 15 January 2020 14:27
> ...
>>>>  		if ((wstate == WRITER_HANDOFF) &&
>>>> -		    (rwsem_spin_on_owner(sem, 0) == OWNER_NULL))
>>>> +		    rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
>>> Nit: the inner braces in the first half of the conditional aren't required
>>> either.
>> I typically over-parenthesize the code to make it easier to read as we
>> don't need to think too much about operator precedence to see if it is
>> doing the right thing.
> The problem is it actually makes it harder to read.
> It is difficult for the 'mark 1 eyeball' to follow lots of sets of brackets.
> Since == (etc) are the lowest priority operators (apart from ?:) they
> never need ().
>
> 	David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>
It depends. I find it hard to read an expression with "&" and "&&"
without parentheses. Anyway, I will admit that the above code is
inconsistent in term of how parentheses are used. So I will change that.

Cheers,
Longman