Re: [PATCH v4 64/66] nommu: Remove uses of VMA linked list

[Liam Howlett]

* Vlastimil Babka <vbabka@xxxxxxx> [220120 12:06]:
> On 1/20/22 16:54, Matthew Wilcox wrote:
> > On Thu, Jan 20, 2022 at 04:06:21PM +0100, Vlastimil Babka wrote:
> >> On 12/1/21 15:30, Liam Howlett wrote:
> >> > From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> >> > 
> >> > Use the maple tree or VMA iterator instead.  This is faster and will
> >> > allow us to shrink the VMA.
> >> > 
> >> > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> >> > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> >> 
> >> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> >> 
> >> But I think some fixup needed:
> >> 
> >> > @@ -1456,12 +1458,14 @@ void exit_mmap(struct mm_struct *mm)
> >> >  
> >> >  	mm->total_vm = 0;
> >> >  
> >> > -	while ((vma = mm->mmap)) {
> >> > -		mm->mmap = vma->vm_next;
> >> > +	mmap_write_lock(mm);
> >> 
> >> If locking was missing, should have been added sooner than now?
> > 
> > I don't think so?  This is the exit_mmap() path, so we know nobody
> > has access to the mm.  We didn't need to hold the lock at this point
> > before, but now for_each_vma() will check we're holding the mmap_lock.
> 
> It has crossed my mind that it is there to make asserts happy, in which case
> a clarifying comment would be useful.

I will add the comment.

> 
> >> > +	for_each_vma(vmi, vma) {
> >> >  		delete_vma_from_mm(vma);
> >> >  		delete_vma(mm, vma);
> >> >  		cond_resched();
> >> >  	}
> >> > +	__mt_destroy(&mm->mm_mt);
> >> 
> >> And this at the point mm_mt was added?
> > 
> > You mean we should have been calling __mt_destroy() earlier in the
> > patch series?
> 
> Yeah.
> 
> > Umm ... I'll defer to Liam on that one.

Yes, I will move this to the correct patch.