linux-kernel - Re: [PATCH -next RFC v2 8/8] sbitmap: wake up the number of threads based on required tags

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Date:   Mon, 11 Apr 2022 20:20:32 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     "yukuai (C)" <yukuai3@...wei.com>, axboe@...nel.dk,
        andriy.shevchenko@...ux.intel.com, john.garry@...wei.com,
        ming.lei@...hat.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH -next RFC v2 8/8] sbitmap: wake up the number of threads
 based on required tags

On 4/9/22 00:01, yukuai (C) wrote:
> For the race that new threads are waited after get_wake_nr() and before
> wake_up_nr() in situation (b), I can't figure out how this can be
> problematic [ ... ]

If the atomic_dec_return() statement in __sbq_wake_up() returns a value 
that is less than or equal to zero, wake_batch waiters should be woken 
up or I/O will hang until sbitmap_queue_wake_all() is called. That last 
function should not be called unless there is no alternative.

Thanks,

Bart.