Re: [PATCH 2.6.21-rc3-mm2 3/4] futex_requeue_pi optimization

[Pierre Peiffer]

Peter Zijlstra a écrit :
> > +static void *get_futex_address(union futex_key *key)
> > +{
> > +	void *uaddr;
> > +
> > +	if (key->both.offset & 1) {
> > +		/* shared mapping */
> > +		uaddr = (void*)((key->shared.pgoff << PAGE_SHIFT)
> > +				+ key->shared.offset - 1);
> > +	} else {
> > +		/* private mapping */
> > +		uaddr = (void*)(key->private.address + key->private.offset);
> > +	}
> > +
> > +	return uaddr;
> > +}
>
> This will not work for nonlinear vmas, granted, not a lot of ppl stick
> futexes in nonlinear vmas, but the futex_key stuff handles it, this
> doesn't.

Indeed ! Thanks for pointing me to this.

Since I'm not familiar with vmm, does this code look more correct to you ?

static void *get_futex_address(union futex_key *key)
{
	void *uaddr;
	struct vm_area_struct *vma = current->mm->mmap;

	if (key->both.offset & 1) {
		/* shared mapping */
		struct file * vmf;

		do {
			if ((vmf = vma->vm_file)
			    && (key->shared.inode == vmf->f_dentry->d_inode))
				break;
			vma = vma->vm_next;
		} while (vma);

		if (likely(!(vma->vm_flags & VM_NONLINEAR)))
			uaddr = (void*)((key->shared.pgoff << PAGE_SHIFT)
					+ key->shared.offset - 1);
		else
			uaddr = (void*) vma->vm_start
				+ ((key->shared.pgoff - vma->vm_pgoff)
				   << PAGE_SHIFT)
				+ key->shared.offset - 1;
	} else {
		/* private mapping */
		uaddr = (void*)(key->private.address + key->private.offset);
	}

	return uaddr;
}

Or is there a more direct way to retrieve the vma corresponding to the given inode ?

Thanks,

--
Pierre
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