On Fri, Aug 21, 2020 at 06:26:15PM -0700, Hugh Dickins wrote:
On Wed, 19 Aug 2020, Greg KH wrote:
On Wed, Aug 19, 2020 at 06:32:26AM -0700, Hugh Dickins wrote:
> On Wed, 19 Aug 2020, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> >
> > This is a note to let you know that I've just added the patch titled
> >
> > khugepaged: khugepaged_test_exit() check mmget_still_valid()
> >
> > to the 5.8-stable tree which can be found at:
> > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> >
> > The filename of the patch is:
> > khugepaged-khugepaged_test_exit-check-mmget_still_valid.patch
> > and it can be found in the queue-5.8 subdirectory.
> >
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@xxxxxxxxxxxxxxx> know about it.
>
> Please hold this one back for the moment: we shall want it, but syzbot
> detected one place where it can lead to a VM_BUG_ON_MM(). The fix to
> that is currently in Andrew's tree, but not yet in Linus's - when it
> gets there, I'll send you its git commit id in reply to this mail.
>
> This patch failed to apply to earlier releases: I'll send the fixup for
> those at that time. (Fixups for another patch to follow later today.)
Now dropped, thanks!
f3f99d63a815 khugepaged: adjust VM_BUG_ON_MM() in __khugepaged_enter()
has now reached Linus's tree, so will reach your tree when you next pull.
When that one is ready, please reinstate this commit that we held back:
bbe98f9cadff khugepaged: khugepaged_test_exit() check mmget_still_valid()
The mmap_sem->mmap_lock change means I must then send you a backport of
bbe98f9cadff for 5.7, 5.4, 4.19, 4.14, 4.9: one backport will do for all
of those, and f3f99d63a815 should cherry-pick cleanly into them all.
But you also marked bbe98f9cadff for 4.4: I had not expected that,
but I think you're right - for whatever reason (probably inertia,
it was tiresome because khugepaged.c got split from huge_memory.c),
4.4 lacks a backport of 59ea6d06cfa9 (though it does have the commit
that depended on), and backports of these two will serve just as well
to fix what it was required to fix: I'll send them too.
Thanks: I'm sorry that this is all so confusing,
kudos to syzbot for catching my error as quickly as it did.
I've followed your instructions and backported the patches:
bbe98f9cadff ("khugepaged: khugepaged_test_exit() check
mmget_still_valid()") - to all branches.
f3f99d63a815 ("khugepaged: adjust VM_BUG_ON_MM() in
__khugepaged_enter()") - to all branches.
59ea6d06cfa9 ("coredump: fix race condition between collapse_huge_page()
and core dumping") - for 4.4.
Thanks!
--
Thanks,
Sasha
