Re: [PATCH v6] sbitmap: fix io hung due to race on sbitmap_word::cleared

[YangYang]

On 2024/7/11 0:41, Bart Van Assche wrote:
> On 7/9/24 11:56 PM, Yang Yang wrote:
> > +    spin_lock_irqsave(&map->swap_lock, flags);
>
> Please use guard(spinlock_irqsave) in new code instead of spin_lock_irqsave() + goto out_unlock 
> + spin_unlock_irqrestore().
> That will make this function significantly easier to read and to
> maintain.

Got it.

> > +
> > +    if (!map->cleared) {
> > +        if (depth > 0) {
> > +            word_mask = (~0UL) >> (BITS_PER_LONG - depth);
> > +            /*
> > +             * The current behavior is to always retry after moving
> > +             * ->cleared to word, and we change it to retry in case
> > +             * of any free bits. To avoid dead loop, we need to take
>
> What is a "dead loop"? Did you perhaps want to write "infinite loop"?

Yeah. I suppose so.

> > +             * wrap & alloc_hint into account. Without this, a soft
> > +             * lockup was detected in our test environment.
>
> Source code comments should not refer to "our test environment". Code
> that is intended for upstream inclusion should work for all setups.

Got it.

> > +             */
> > +            if (!wrap && alloc_hint)
> > +                word_mask &= ~((1UL << alloc_hint) - 1);
>
> Above I see an open-coded __clear_bit() operation. Has it been
> considered to use __clear_bit() instead of open-coding it?

It is meant to reset multiple bits to zero, but __clear_bit() is only
capable of resetting one bit to zero.

Thanks.

> Thanks,
>
> Bart.