linux-kernel - Re: [PATCH v4 1/3] btrfs: add might_sleep() to some places in update_qgroup_limit

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Date:   Tue, 15 Nov 2022 18:41:22 +0100
From:   David Sterba <dsterba@...e.cz>
To:     ChenXiaoSong <chenxiaosong2@...wei.com>
Cc:     clm@...com, josef@...icpanda.com, dsterba@...e.com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhangxiaoxu5@...wei.com, yanaijie@...wei.com,
        quwenruo.btrfs@....com, wqu@...e.com
Subject: Re: [PATCH v4 1/3] btrfs: add might_sleep() to some places in
 update_qgroup_limit_item()

On Wed, Nov 16, 2022 at 01:17:07AM +0800, ChenXiaoSong wrote:
> As the potential sleeping under spin lock is hard to spot, we should add
> might_sleep() to some places.
> 
> Signed-off-by: ChenXiaoSong <chenxiaosong2@...wei.com>
> ---
>  fs/btrfs/ctree.c  | 2 ++
>  fs/btrfs/qgroup.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index a9543f01184c..809053e9cfde 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -1934,6 +1934,8 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>  	int min_write_lock_level;
>  	int prev_cmp;
>  
> +	might_sleep();

This needs some explanation in the changelog, the reason was mentioned
in some past patch iteration that it's due to potential IO fi the blocks
are not cached.

> +
>  	lowest_level = p->lowest_level;
>  	WARN_ON(lowest_level && ins_len > 0);
>  	WARN_ON(p->nodes[0] != NULL);
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 9334c3157c22..d0480b9c6c86 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -779,6 +779,8 @@ static int update_qgroup_limit_item(struct btrfs_trans_handle *trans,
>  	int ret;
>  	int slot;
>  
> +	might_sleep();

This one is redundant, no? There's call to btrfs_search_slot a few lines
below.

> +
>  	key.objectid = 0;
>  	key.type = BTRFS_QGROUP_LIMIT_KEY;
>  	key.offset = qgroup->qgroupid;
> -- 
> 2.31.1
>