linux-kernel - Re: [PATCH v2 1/2] fscache: Use wait_on_bit() to wait for the freeing of relinquished volume

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Message-ID: <4e839278-fadb-24da-3a4e-50e58a0e7cc6@huaweicloud.com>
Date:   Thu, 12 Jan 2023 09:05:22 +0800
From:   Hou Tao <houtao@...weicloud.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-cachefs@...hat.com, Jeff Layton <jlayton@...nel.org>,
        linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Jingbo Xu <jefflexu@...ux.alibaba.com>, houtao1@...wei.com
Subject: Re: [PATCH v2 1/2] fscache: Use wait_on_bit() to wait for the freeing
 of relinquished volume

Hi,

On 1/12/2023 12:06 AM, David Howells wrote:
> Hou Tao <houtao@...weicloud.com> wrote:
>
>>  			clear_bit(FSCACHE_VOLUME_ACQUIRE_PENDING, &cursor->flags);
>> +			/*
>> +			 * Paired with barrier in wait_on_bit(). Check
>> +			 * wake_up_bit() and waitqueue_active() for details.
>> +			 */
>> +			smp_mb__after_atomic();
>>  			wake_up_bit(&cursor->flags, FSCACHE_VOLUME_ACQUIRE_PENDING);
> What two values are you applying a partial ordering to?
cursor->flags and wq->head. fscache_wake_pending_volume() will write
cursor->flags and read wq->head through waitqueue_active(), and the wait will
write wq->head then read cursor->flags.
>
> David
>