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	Tue, 06 May 2025 17:25:39 +0000
Date: Tue, 6 May 2025 18:25:39 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: Klara Modin <klarasmodin@gmail.com>
Cc: linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org
Subject: Re: [RFC][PATCH] btrfs_get_tree_subvol(): switch from fc_mount() to
 vfs_create_mount()
Message-ID: <20250506172539.GN2023217@ZenIV>
References: <20250505030345.GD2023217@ZenIV>
 <3qdz7ntes5ufac7ldgfsrnvotk4izalmtdf7opqox5mk3kpxus@gabtxt27uwah>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Tue, May 06, 2025 at 03:36:03PM +0200, Klara Modin wrote:

>   25:	49 8b 44 24 60       	mov    0x60(%r12),%rax
	rax = fc->root
>   2a:*	48 8b 78 68          	mov    0x68(%rax),%rdi		<-- trapping instruction
	rdi = rax->d_sb, hitting rax == 0

> > -	mnt = fc_mount(dup_fc);
> > -	if (IS_ERR(mnt)) {
> > -		put_fs_context(dup_fc);
> > -		return PTR_ERR(mnt);
> > +	ret = vfs_get_tree(dup_fc);
> > +	if (!ret) {
> > +		ret = btrfs_reconfigure_for_mount(dup_fc);
> > +		up_write(&fc->root->d_sb->s_umount);

... here.  D'oh...  Should be dup_fc, obviously - fc->root hadn't been
set yet.  Make that line
		up_write(&dup_fc->root->d_sb->s_umount);
and see if it helps.  Sorry about the braino...