linux-ext4 - Re: [PATCH] ext4: Add periodic superblock update check

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Message-ID: <20230804205809.GE903325@mit.edu>
Date:   Fri, 4 Aug 2023 16:58:09 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Vitaliy Kuznetsov <vk.en.mail@...il.com>
Cc:     linux-ext4@...r.kernel.org, adilger@...ger.ca
Subject: Re: [PATCH] ext4: Add periodic superblock update check

On Mon, Jul 31, 2023 at 04:25:26PM +0400, Vitaliy Kuznetsov wrote:
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index 6d332dff79dd..9f334de4f636 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -515,7 +515,8 @@ static const struct kobj_type ext4_feat_ktype = {
> 
>  void ext4_notify_error_sysfs(struct ext4_sb_info *sbi)
>  {
> -	sysfs_notify(&sbi->s_kobj, NULL, "errors_count");
> +	if (sbi->s_add_error_count > 0)
> +		sysfs_notify(&sbi->s_kobj, NULL, "errors_count");
>  }

The problem is that ext4_notify_error_sysfs() is called in
flush_stashed_error_work() **after** that function calls
ext4_update_super() --- and ext4_update_super will zero out
s_add_error_count.  So this will result in the sysfs_notify call
*never* getting called, which would be a regression.  So
unfortunately, I can't accept this patch as currently written.

Fortunately, only flush_stashed_error_work() calls
ext4_notify_error_sysfs(), so it should be easy enough to sample
s_add_error_count before calling ext4_update_super(), and then
conditionally call sysfs_notify() if it is non-zero.

	      	   		     	   - Ted