linux-ext4 - Re: [PATCH 1/2] ext4: use XATTR_CREATE in ext4

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Date:   Thu, 10 May 2018 11:54:27 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Eryu Guan <guaneryu@...il.com>
Cc:     linux-ext4@...r.kernel.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Tahsin Erdogan <tahsin@...gle.com>
Subject: Re: [PATCH 1/2] ext4: use XATTR_CREATE in ext4_initxattrs()

On Thu, Apr 26, 2018 at 07:20:26PM +0800, Eryu Guan wrote:
> I hit ENOSPC error when creating new file in a newly created ext4
> with ea_inode feature enabled, if selinux is enabled and ext4 is
> mounted without any selinux context. e.g.
> 
>   mkfs -t ext4 -O ea_inode -F /dev/sda5
>   mount /dev/sda5 /mnt/ext4
>   touch /mnt/ext4/testfile  # got ENOSPC here
> 
> It turns out that we run out of journal credits in
> ext4_xattr_set_handle() when creating new selinux label for the
> newly created inode.
> 
> This is because that in __ext4_new_inode() we use
> __ext4_xattr_set_credits() to calculate the reserved credits for new
> xattr, with the 'is_create' argument being true, which implies less
> credits in the ea_inode case. But we calculate the required credits
> in ext4_xattr_set_handle() with 'is_create' being false, which means
> we need more credits if ea_inode feature is enabled. So we don't
> have enough credits and error out with ENOSPC.
> 
> Fix it by simply calling ext4_xattr_set_handle() with XATTR_CREATE
> flag in ext4_initxattrs(), so we end up with requiring less credits
> than reserved. The semantic of XATTR_CREATE is "Perform a pure
> create, which fails if the named attribute exists already." (from
> setxattr(2)), which is fine in this case, because we only call
> ext4_initxattrs() on newly created inode.
> 
> Fixes: af65207c76ce ("ext4: fix __ext4_new_inode() journal credits calculation")
> Cc: Tahsin Erdogan <tahsin@...gle.com>
> Signed-off-by: Eryu Guan <guaneryu@...il.com>

Thanks, applied.

					- Ted