Re: [PATCH v2 1/3] seqlock: add raw_seqcount_try_begin

[David Hildenbrand <david@redhat.com>]

On 22.11.24 12:19, Peter Zijlstra wrote:
> On Fri, Nov 22, 2024 at 12:10:29PM +0100, David Hildenbrand wrote:
> 
>> In gup_fast(), we simply do
>>
>> seq = raw_read_seqcount(&current->mm->write_protect_seq);
>> if (seq & 1)
>> 	return 0;
>>
>> Should we be using that there as well?
>>
>> if (!raw_seqcount_try_begin(&current->mm->write_protect_seqs, seq))
>> 	return 0;
> 
> Might as well. A quick grep doesn't find me another instance of this
> pattern, but does find me something 'funny' in net/netfilter/x_tables.c.
> Let's pretend I didn't see that for now ... *sigh*

:)

I'm also not 100% sure about barriers in gup_fast() around the 
raw_seqcount .... and I'm pretending I didn't see any of that as well ...

> 
> Want me to stick a patch like this on, or do you want to do that later,
> when the dust has settled?

Feel free to add a patch to just change that as well, it's an easy change.

For this patch

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb