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SubjectRe: [PATCH] fuse: avoid deadlock when write fuse inode
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Hi all,


This patch works well in our product, but I am not sure this is the correct

way to solve this problem. I think that the inode->i_count shouldn't be

zero after iput is executed in dentry_unlink_inode, then the inode won't

be writeback. But i haven't found where iget is missing.


Thanks,

Jianan

On 2021/2/2 12:08, Huang Jianan 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
>
> The request and inode processed by Thread A and B are the same, which
> causes a deadlock. To avoid this, we remove the __GFP_FS flag when
> allocating memory in fuse_copy_fill, so there will be no memory
> reclaimation in super_cache_scan.
>
> Signed-off-by: Huang Jianan <huangjianan@oppo.com>
> Signed-off-by: Guo Weichao <guoweichao@oppo.com>
> ---
> fs/fuse/dev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 588f8d1240aa..e580b9d04c25 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -721,7 +721,7 @@ static int fuse_copy_fill(struct fuse_copy_state *cs)
> if (cs->nr_segs >= cs->pipe->max_usage)
> return -EIO;
>
> - page = alloc_page(GFP_HIGHUSER);
> + page = alloc_page(GFP_HIGHUSER & ~__GFP_FS);
> if (!page)
> return -ENOMEM;
>

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