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

[YangYang <yang.yang@vivo.com>]

On 2024/7/11 3:54, Bart Van Assche wrote:
> On 7/9/24 11:56 PM, Yang Yang wrote:
>> +    /**
>> +     * @swap_lock: Held while swapping word <-> cleared
>> +     */
>> +    spinlock_t swap_lock;
> 
> Why is only swapping 'word' with 'cleared' protected by the spinlock?
> If all 'cleared' changes would be protected by this spinlock then
> that would allow to eliminate the expensive xchg() call from
> sbitmap_deferred_clear().

The spinlock was initially introduced in ea86ea2cdced ("sbitmap:
ammortize cost of clearing bits").
I think if all 'cleared' changes are protected by the spinlock, the
overhead of clearing tags would definitely increase.

Thanks.

> 
> Thanks,
> 
> Bart.