Re: [Xen-devel] [PATCH v5 6/8] mm: Keep heap accessible to others while scrubbing

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> 07/23/17 4:28 AM >>>
>On 06/27/2017 03:28 PM, Jan Beulich wrote:
>>>>> Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> 06/22/17 8:56 PM >>>
>>> +static void check_and_stop_scrub(struct page_info *head)
>>> +{
>>> +    if ( head->u.free.scrub_state == BUDDY_SCRUBBING )
>>> +    {
>>> +        struct page_info pg;
>>> +
>>> +        head->u.free.scrub_state = BUDDY_SCRUB_ABORT;
>>> +        spin_lock_kick();
>>> +        for ( ; ; )
>>> +        {
>>> +            /* Can't ACCESS_ONCE() a bitfield. */
>>> +            pg.u.free.val = ACCESS_ONCE(head->u.free.val);
>> 
>> Something like ACCESS_ONCE(head->u.free).val ought to work (or read_atomic(),
>> due to the questionable scalar type check in ACCESS_ONCE()).
>
>Hmm... I couldn't get this to work with either suggestion.
>
>page_alloc.c:751:13: error: conversion to non-scalar type requested
>pg.u.free = read_atomic(&head->u.free);
>
>page_alloc.c:753:6: error: conversion to non-scalar type requested
>if ( ACCESS_ONCE(head->u.free).scrub_state != BUDDY_SCRUB_ABORT )

Oh, indeed. That's rather unfortunate.

Jan


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