linux-kernel - Re: [RFC 1/3] x86/vdso: create vdso file, use it for mapping

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Message-ID: <20160903002051.GA2356@ZenIV.linux.org.uk>
Date:   Sat, 3 Sep 2016 01:20:52 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        luto@...capital.net, tglx@...utronix.de, hpa@...or.com,
        x86@...nel.org, 0x7f454c46@...il.com, oleg@...hat.com,
        rostedt@...dmis.org
Subject: Re: [RFC 1/3] x86/vdso: create vdso file, use it for mapping

On Thu, Aug 25, 2016 at 06:21:08PM +0300, Dmitry Safonov wrote:
> +		unsigned long n_addr = mmap_region(vdso_file_64, text_start,
> +				image->size, VM_READ|VM_EXEC|
> +				VM_DONTEXPAND|VM_SOFTDIRTY|
> +				VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0);
> +		if (text_start != n_addr) {
> +			pr_err("Failed to mmap vdso file at %lx, mmap_region returned %lx\n",
> +					text_start, n_addr);
> +			goto old_way;
> +		}
> +		vma = find_vma(mm, text_start);
> +		if (IS_ERR(vma) || vma->vm_start != text_start) {
> +			pr_err("Failed to find vdso mapped vma at %lx\n",
> +					text_start);
> +			goto old_way;

Umm...  Since when can find_vma() return ERR_PTR()?

> +	d_set_d_op(path.dentry, &vdso_dops);

Nope.  Set ->s_d_op to &vdso_dops and be done with that.

> +static struct file_system_type vdso_fs_type = {
> +	.name		= "vdsofs",
> +	.mount		= ramfs_mount,

Probably the wrong thing here.  Just use a simple wrapper using mount_pseudo()
for all work; see fs/aio.c:aio_mount().

> +	ret = register_filesystem(&vdso_fs_type);

Do you really want it user-mountable?  If not, no need to register...