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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Mon, 5 Sep 2022 15:28:21 +0200
Message-ID: <CAJfpegs6Jbr8eF9ZNycEjfCtJNVQJECjFnOC9-v8WSXHvpWxCg@mail.gmail.com>
Subject: Re: [PATCH] fuse: fix the deadlock in race of reclaim path with kswapd
To:     Kassey Li <quic_yingangl@quicinc.com>
Cc:     linux-fsdevel@vger.kernel.org, quic_maow@quicinc.com,
        linux-kernel@vger.kernel.org
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On Mon, 5 Sept 2022 at 09:17, Kassey Li <quic_yingangl@quicinc.com> wrote:
>
> Task A wait for writeback, while writeback Task B send request to fuse.
> Task C is expected to serve this request, here it is in direct reclaim
> path cause deadlock when system is in low memory.
>
> without __GFP_FS in Task_C break throttle_direct_reclaim with an
> HZ timeout.
>
> kswpad (Task_A):                    writeback(Task_B):
>     __switch_to+0x14c                   schedule+0x70
>     __schedule+0xb5c                    __fuse_request_send+0x154
>     schedule+0x70                       fuse_simple_request+0x184
>     bit_wait+0x18                       fuse_flush_times+0x114
>     __wait_on_bit+0x74                  fuse_write_inode+0x60
>     inode_wait_for_writeback+0xa4       __writeback_single_inode+0x3d8
>     evict+0xa8                          writeback_sb_inodes+0x4c0
>     iput+0x248                          __writeback_inodes_wb+0xb0
>     dentry_unlink_inode+0xdc            wb_writeback+0x270
>     __dentry_kill[jt]+0x110             wb_workfn+0x37c
>     shrink_dentry_list+0x17c            process_one_work+0x284
>     prune_dcache_sb+0x5c
>     super_cache_scan+0x11c
>     do_shrink_slab+0x248
>     shrink_slab+0x260
>     shrink_node+0x678
>     kswapd+0x8ec
>     kthread+0x140
>     ret_from_fork+0x10
>
> Task_C:
>     __switch_to+0x14c
>     __schedule+0xb5c
>     schedule+0x70
>     throttle_direct_reclaim
>     try_to_free_pages
>     __perform_reclaim
>     __alloc_pages_direct_reclaim
>     __alloc_pages_slowpath
>     __alloc_pages_nodemask
>     alloc_pages
>     fuse_copy_fill+0x168
>     fuse_dev_do_read+0x37c
>     fuse_dev_splice_read+0x94

Should already be fixed in v5.16 by commit 5c791fe1e2a4 ("fuse: make
sure reclaim doesn't write the inode").

Thanks,
Miklos