Re: [PATCH v2] mm/gup: fix try_grab_compound_head() race with split_huge_page()

[Vlastimil Babka]

On 6/16/21 8:40 PM, Yang Shi wrote:
> On Wed, Jun 16, 2021 at 10:27 AM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>>
>> On 6/16/21 1:10 AM, Yang Shi wrote:
>> > On Tue, Jun 15, 2021 at 5:10 AM Jann Horn <jannh@xxxxxxxxxx> wrote:
>> >>
>> >
>> > It might be possible after Mel's "mm/page_alloc: Allow high-order
>> > pages to be stored on the per-cpu lists" patch
>> > (https://patchwork.kernel.org/project/linux-mm/patch/20210611135753.GC30378@xxxxxxxxxxxxxxxxxxx/).
>>
>> Those would be percpu indeed, but not "lockless, non-atomic", no? They are
>> protected by a local_lock.
> 
> The local_lock is *not* a lock on non-PREEMPT_RT kernel IIUC. It
> disables preempt and IRQ. But preempt disable is no-op on non-preempt
> kernel. IRQ disable can guarantee it is atomic context, but I'm not
> sure if it is equivalent to "atomic freelists" in Jann's context.

Hm right, I thought all locks had the acquire/release semantics, but this one is
just a barrier().