linux-kernel - Re: [PATCH] ext4: use rcu API in debug_print

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Message-ID: <20191213113510.GG15474@quack2.suse.cz>
Date:   Fri, 13 Dec 2019 12:35:10 +0100
From:   Jan Kara <jack@...e.cz>
To:     Phong Tran <tranmanphong@...il.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca, paulmck@...nel.org,
        joel@...lfernandes.org, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org, rcu@...r.kernel.org
Subject: Re: [PATCH] ext4: use rcu API in debug_print_tree

On Sun 01-12-19 10:51:07, Phong Tran wrote:
> struct ext4_sb_info.system_blks was marked __rcu.
> But access the pointer without using RCU lock and dereference.
> Sparse warning with __rcu notation:
> 
> block_validity.c:139:29: warning: incorrect type in argument 1 (different address spaces)
> block_validity.c:139:29:    expected struct rb_root const *
> block_validity.c:139:29:    got struct rb_root [noderef] <asn:4> *
> 
> Signed-off-by: Phong Tran <tranmanphong@...il.com>

Thanks for the patch. It looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/block_validity.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
> index d4d4fdfac1a6..1ee04e76bbe0 100644
> --- a/fs/ext4/block_validity.c
> +++ b/fs/ext4/block_validity.c
> @@ -133,10 +133,13 @@ static void debug_print_tree(struct ext4_sb_info *sbi)
>  {
>  	struct rb_node *node;
>  	struct ext4_system_zone *entry;
> +	struct ext4_system_blocks *system_blks;
>  	int first = 1;
>  
>  	printk(KERN_INFO "System zones: ");
> -	node = rb_first(&sbi->system_blks->root);
> +	rcu_read_lock();
> +	system_blks = rcu_dereference(sbi->system_blks);
> +	node = rb_first(&system_blks->root);
>  	while (node) {
>  		entry = rb_entry(node, struct ext4_system_zone, node);
>  		printk(KERN_CONT "%s%llu-%llu", first ? "" : ", ",
> @@ -144,6 +147,7 @@ static void debug_print_tree(struct ext4_sb_info *sbi)
>  		first = 0;
>  		node = rb_next(node);
>  	}
> +	rcu_read_unlock();
>  	printk(KERN_CONT "\n");
>  }
>  
> -- 
> 2.20.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR