On Thu, Feb 04, 2021 at 09:11:24PM -0800, Mike Kravetz wrote: [...] > >>> @@ -3787,7 +3803,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, > >>> dst_entry = huge_ptep_get(dst_pte); > >>> if ((dst_pte == src_pte) || !huge_pte_none(dst_entry)) > >>> continue; > >>> - > >>> +again: > >>> dst_ptl = huge_pte_lock(h, dst, dst_pte); > >>> src_ptl = huge_pte_lockptr(h, src, src_pte); > >>> spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); > > > > Side question: Mike, do you know why we need this lock_nested()? Could the src > > lock be taken due to any reason already? It confused me when I read the chunk. > > I see that it was added with commit 4647875819aa. That was when huge pages > used the single per-mm ptl. Lockdep seemed to complain about taking > &mm->page_table_lock twice. Certainly, source and destination mm can not > be the same. Right? Right, at least that's my understanding.. > I do not have the full history, but it 'looks' like > lockdep might have been confused and this was added to keep it quiet. > > BTW - Copy page range for 'normal' pages has the same spin_lock_nested(). Yes. I'll need to take the same lock in v3, so I think I'll just follow. Thanks, -- Peter Xu
