linux-kernel - Re: [PATCH v11 03/22] cachefiles: unbind cachefiles gracefully in on-demand mode

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Date:   Tue, 10 May 2022 13:53:18 +0100
From:   David Howells <dhowells@...hat.com>
To:     Jeffle Xu <jefflexu@...ux.alibaba.com>
Cc:     dhowells@...hat.com, linux-cachefs@...hat.com, xiang@...nel.org,
        chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        torvalds@...ux-foundation.org, gregkh@...uxfoundation.org,
        willy@...radead.org, linux-fsdevel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com, bo.liu@...ux.alibaba.com,
        tao.peng@...ux.alibaba.com, gerry@...ux.alibaba.com,
        eguan@...ux.alibaba.com, linux-kernel@...r.kernel.org,
        luodaowen.backend@...edance.com, tianzichen@...ishou.com,
        yinxin.x@...edance.com, zhangjiachen.jaycee@...edance.com,
        zhujia.zj@...edance.com
Subject: Re: [PATCH v11 03/22] cachefiles: unbind cachefiles gracefully in on-demand mode

Jeffle Xu <jefflexu@...ux.alibaba.com> wrote:

> Add a refcount to avoid the deadlock in on-demand read mode. The
> on-demand read mode will pin the corresponding cachefiles object for
> each anonymous fd. The cachefiles object is unpinned when the anonymous
> fd gets closed. When the user daemon exits and the fd of
> "/dev/cachefiles" device node gets closed, it will wait for all
> cahcefiles objects getting withdrawn. Then if there's any anonymous fd
> getting closed after the fd of the device node, the user daemon will
> hang forever, waiting for all objects getting withdrawn.
> 
> To fix this, add a refcount indicating if there's any object pinned by
> anonymous fds. The cachefiles cache gets unbound and withdrawn when the
> refcount is decreased to 0. It won't change the behaviour of the
> original mode, in which case the cachefiles cache gets unbound and
> withdrawn as long as the fd of the device node gets closed.
> 
> Signed-off-by: Jeffle Xu <jefflexu@...ux.alibaba.com>

Acked-by: David Howells <dhowells@...hat.com>