linux-kernel - Re: [fuse-devel] [PATCH] fuse: avoid deadlock when write fuse inode

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Date:   Wed, 24 Mar 2021 16:28:35 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Huang Jianan <huangjianan@...o.com>
Cc:     linux-kernel@...r.kernel.org, guoweichao@...o.com,
        zhangshiming@...o.com, linux-fsdevel@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>,
        Ed Tsai (蔡宗軒) <Ed.Tsai@...iatek.com>
Subject: Re: [fuse-devel] [PATCH] fuse: avoid deadlock when write fuse inode

On Tue, Feb 2, 2021 at 5:41 AM Huang Jianan via fuse-devel
<fuse-devel@...ts.sourceforge.net> wrote:
>
> We found the following deadlock situations in low memory scenarios:
> Thread A                         Thread B
> - __writeback_single_inode
>  - fuse_write_inode
>   - fuse_simple_request
>    - __fuse_request_send
>     - request_wait_answer
>                                  - fuse_dev_splice_read
>                                   - fuse_copy_fill
>                                    - __alloc_pages_direct_reclaim
>                                     - do_shrink_slab
>                                      - super_cache_scan
>                                       - shrink_dentry_list
>                                        - dentry_unlink_inode
>                                         - iput_final
>                                          - inode_wait_for_writeback

On what kernel are you seeing this?

I don't see how it can happen on upstream kernels, since there's a
"write_inode_now(inode, 1)" call in fuse_release() and nothing can
dirty the inode after the file has been released.

Thanks,
Miklos