linux-kernel - Re: [PATCH] writeback: safer lock nesting

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Message-ID: <20180406080714.GG8286@dhcp22.suse.cz>
Date:   Fri, 6 Apr 2018 10:07:14 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Greg Thelen <gthelen@...gle.com>
Cc:     Wang Long <wanglong19@...tuan.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, npiggin@...il.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] writeback: safer lock nesting

On Fri 06-04-18 01:03:24, Greg Thelen wrote:
[...]
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index d4d04fee568a..d51bae5a53e2 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -746,10 +746,11 @@ int inode_congested(struct inode *inode, int cong_bits)
>  	if (inode && inode_to_wb_is_valid(inode)) {
>  		struct bdi_writeback *wb;
>  		bool locked, congested;
> +		unsigned long flags;
>  
> -		wb = unlocked_inode_to_wb_begin(inode, &locked);
> +		wb = unlocked_inode_to_wb_begin(inode, &locked, &flags);

Wouldn't it be better to have a cookie (struct) rather than 2 parameters
and let unlocked_inode_to_wb_end DTRT?

>  		congested = wb_congested(wb, cong_bits);
> -		unlocked_inode_to_wb_end(inode, locked);
> +		unlocked_inode_to_wb_end(inode, locked, flags);
>  		return congested;
>  	}
-- 
Michal Hocko
SUSE Labs