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@linuxfoundation.org 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%3Ba=su...
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@vger.kernel.org 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.
Hugh