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Date:   Thu, 15 Oct 2020 01:33:24 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Jan Kara <jack@...e.cz>
Cc:     Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: Re: [PATCH] ext4: Detect already used quota file early

On Oct 13, 2020, at 7:22 AM, Jan Kara <jack@...e.cz> wrote:
> 
> When we try to use file already used as a quota file again (for the same
> or different quota type), strange things can happen. At the very least
> lockdep annotations may be wrong but also inode flags may be wrongly set
> / reset. When the file is used for two quota types at once we can even
> corrupt the file and likely crash the kernel. Catch all these cases by
> checking whether passed file is already used as quota file and bail
> early in that case.
> 
> This fixes occasional generic/219 failure due to lockdep complaint.
> 
> Reported-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> Signed-off-by: Jan Kara <jack@...e.cz>

Patch looks OK, but a minor question/suggestion below...

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index ea425b49b345..49b2e6be35c4 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -6042,6 +6042,11 @@ static int ext4_quota_on(struct super_block *sb, int type, int format_id,
> 	/* Quotafile not on the same filesystem? */
> 	if (path->dentry->d_sb != sb)
> 		return -EXDEV;
> +
> +	/* Quota already enabled for this file? */
> +	if (path->dentry->d_inode->i_flags & S_NOQUOTA)
> +		return -EBUSY;

Any reason not to use IS_NOQUOTA(path->dentry->d_inode) here?  I was trying
to see where S_NOQUOTA is set, and it seems that all of the quota code is
using IS_NOQUOTA().


Cheers, Andreas






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