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Message-ID: <CADrL8HXzV2fF3OHf3pk6EJn8Z0=b8NHpRCD9GBcw9y1UTc5goA@mail.gmail.com>
Date: Mon, 21 Nov 2022 10:11:23 -0800
From: James Houghton <jthoughton@...gle.com>
To: Peter Xu <peterx@...hat.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>,
Muchun Song <songmuchun@...edance.com>,
David Hildenbrand <david@...hat.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Mina Almasry <almasrymina@...gle.com>,
"Zach O'Keefe" <zokeefe@...gle.com>,
Manish Mishra <manish.mishra@...anix.com>,
Naoya Horiguchi <naoya.horiguchi@....com>,
"Dr . David Alan Gilbert" <dgilbert@...hat.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Vlastimil Babka <vbabka@...e.cz>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Yang Shi <shy828301@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 05/47] hugetlb: make hugetlb_vma_lock_alloc return
its failure reason
On Wed, Nov 16, 2022 at 9:08 AM Peter Xu <peterx@...hat.com> wrote:
>
> No objection on the patch itself, but I am just wondering what guarantees
> thread-safety for this function to not leak vm_private_data when two
> threads try to allocate at the same time.
>
> I think it should be the write mmap lock. I saw that in your latest code
> base there's:
>
> /*
> * We must hold the mmap lock for writing so that callers can rely on
> * hugetlb_hgm_enabled returning a consistent result while holding
> * the mmap lock for reading.
> */
> mmap_assert_write_locked(vma->vm_mm);
>
> /* HugeTLB HGM requires the VMA lock to synchronize collapsing. */
> ret = hugetlb_vma_data_alloc(vma);
> if (ret)
> return ret;
>
> So that's covered there. The rest places are hugetlb_vm_op_open() and
> hugetlb_reserve_pages() and they all seem fine too: hugetlb_vm_op_open() is
> during mmap(), the latter has vma==NULL so allocation will be skipped.
>
> I'm wondering whether it would make sense to move this assert to be inside
> of hugetlb_vma_data_alloc() after the !vma check, or just add the same
> assert too but for different reason.
I think leaving the assert here and adding a new assert inside
hugetlb_vma_data_alloc() makes sense. Thanks Peter.
- James
>
> >
> > vma_lock = kmalloc(sizeof(*vma_lock), GFP_KERNEL);
> > if (!vma_lock) {
> > @@ -7026,13 +7026,14 @@ static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
> > * allocation failure.
> > */
> > pr_warn_once("HugeTLB: unable to allocate vma specific lock\n");
> > - return;
> > + return -ENOMEM;
> > }
> >
> > kref_init(&vma_lock->refs);
> > init_rwsem(&vma_lock->rw_sema);
> > vma_lock->vma = vma;
> > vma->vm_private_data = vma_lock;
> > + return 0;
> > }
> >
> > /*
> > @@ -7160,8 +7161,9 @@ static void hugetlb_vma_lock_free(struct vm_area_struct *vma)
> > {
> > }
> >
> > -static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
> > +static int hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
> > {
> > + return 0;
> > }
> >
> > pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
> > --
> > 2.38.0.135.g90850a2211-goog
> >
> >
>
> --
> Peter Xu
>
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