From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Xu <peterx@redhat.com>
Cc: Linux MM Mailing List <linux-mm@kvack.org>,
Jason Gunthorpe <jgg@nvidia.com>,
John Hubbard <jhubbard@nvidia.com>, Jan Kara <jack@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: Possible race with page_maybe_dma_pinned?
Date: Wed, 29 Sep 2021 15:47:05 -0700 [thread overview]
Message-ID: <CAHk-=wjdiXyXFukBUwLKdSXRrwTzyRnynLFvJUe1BM4D6wBvsw@mail.gmail.com> (raw)
In-Reply-To: <YVTFEAwHEZfUrSCT@t490s>
On Wed, Sep 29, 2021 at 12:57 PM Peter Xu <peterx@redhat.com> wrote:
>
> Now we have 3 callers of page_maybe_dma_pinned():
>
> 1. page_needs_cow_for_dma
> 2. pte_is_pinned
> 3. shrink_page_list
>
> The 1st one is good as it takes the seqlock for write properly. The 2nd & 3rd
> are missing, we may need to add them.
Well, the pte_is_pinned() case at least could do the seqlock in
clear_soft_dirty() - it has the vma and mm available.
The page shrinker has always been problematic since it doesn't have
the vm (and by "always" I mean "modern times" - long ago we used to
scan virtually, in the days before rmap)
One option might be for fast-gup to give up on locked pages. I think
the page lock is the only thing that shrink_page_list() serializes
with.
Linus
next prev parent reply other threads:[~2021-09-29 22:47 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 19:57 Peter Xu
2021-09-29 22:47 ` Linus Torvalds [this message]
2021-09-30 1:57 ` John Hubbard
2021-09-30 11:11 ` Jan Kara
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