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Re: [PATCH v4 10/12] xen/spinlock: split recursive spinlocks from normal ones
- To: Juergen Gross <jgross@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 4 Mar 2024 08:25:23 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 04 Mar 2024 07:25:40 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 01.03.2024 15:37, Juergen Gross wrote:
> On 29.02.24 16:32, Jan Beulich wrote:
>> On 12.12.2023 10:47, Juergen Gross wrote:
>>> +#define nrspin_lock_irqsave(l, f) \
>>> + ({ \
>>> + BUILD_BUG_ON(sizeof(f) != sizeof(unsigned long)); \
>>> + ((f) = __nrspin_lock_irqsave(l)); \
>>
>> I don't think the outer pair of parentheses is needed here.
>
> Turns out it is needed. Otherwise something like:
>
>
> if ( a )
> nrspin_lock_irqsave(l, f);
> else
> ...
>
> will fail with "else without a previous if".
That's for "outer" in the whole #define I suppose, when I commented on
just a specific line inside the construct. The ({ ... }) may better be
avoided here too, for there being no reason to use a compiler
extension when do { ... } while ( false ) would also do. Things would
be different in the construct "returned" the flags value, in a more
function-like manner. But that would be inconsistent with related
similar functions.
Jan
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