Messages in this thread | | | From | Suren Baghdasaryan <> | Date | Thu, 8 Sep 2022 16:57:17 -0700 | Subject | Re: [RFC PATCH RESEND 07/28] kernel/fork: mark VMAs as locked before copying pages during fork |
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On Tue, Sep 6, 2022 at 7:38 AM Laurent Dufour <ldufour@linux.ibm.com> wrote: > > Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit : > > Protect VMAs from concurrent page fault handler while performing > > copy_page_range for VMAs having VM_WIPEONFORK flag set. > > I'm wondering why is that necessary. > The copied mm is write locked, and the destination one is not reachable. > If any other readers are using the VMA, this is only for page fault handling.
Correct, this is done to prevent page faulting in the VMA being duplicated. I assume we want to prevent the pages in that VMA from changing when we are calling copy_page_range(). Am I wrong?
> I should have miss something because I can't see any need to mark the lock > VMA here. > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com> > > --- > > kernel/fork.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/fork.c b/kernel/fork.c > > index bfab31ecd11e..1872ad549fed 100644 > > --- a/kernel/fork.c > > +++ b/kernel/fork.c > > @@ -709,8 +709,10 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, > > rb_parent = &tmp->vm_rb; > > > > mm->map_count++; > > - if (!(tmp->vm_flags & VM_WIPEONFORK)) > > + if (!(tmp->vm_flags & VM_WIPEONFORK)) { > > + vma_mark_locked(mpnt); > > retval = copy_page_range(tmp, mpnt); > > + } > > > > if (tmp->vm_ops && tmp->vm_ops->open) > > tmp->vm_ops->open(tmp); >
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