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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <20220509074028.74954-4-jefflexu@linux.alibaba.com>
References: <20220509074028.74954-4-jefflexu@linux.alibaba.com> <20220509074028.74954-1-jefflexu@linux.alibaba.com>
To:     Jeffle Xu <jefflexu@linux.alibaba.com>
Cc:     dhowells@redhat.com, linux-cachefs@redhat.com, xiang@kernel.org,
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Subject: Re: [PATCH v11 03/22] cachefiles: unbind cachefiles gracefully in on-demand mode
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Content-ID: <3509260.1652187198.1@warthog.procyon.org.uk>
Date:   Tue, 10 May 2022 13:53:18 +0100
Message-ID: <3509261.1652187198@warthog.procyon.org.uk>
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Jeffle Xu <jefflexu@linux.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 cahcefiles objects getting withdrawn.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 hang forever, waiting for all objects getting withdrawn.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 The cachefiles cache gets unbound and withdrawn when the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 withdrawn as long as the fd of the device node gets closed.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@linux.alibaba.com>

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