Patch "mm/hugetlb: fix missing hugetlb_lock for resv uncharge" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    mm/hugetlb: fix missing hugetlb_lock for resv uncharge

to the 6.6-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:
     mm-hugetlb-fix-missing-hugetlb_lock-for-resv-uncharge.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From b76b46902c2d0395488c8412e1116c2486cdfcb2 Mon Sep 17 00:00:00 2001
From: Peter Xu <peterx@xxxxxxxxxx>
Date: Wed, 17 Apr 2024 17:18:35 -0400
Subject: mm/hugetlb: fix missing hugetlb_lock for resv uncharge

From: Peter Xu <peterx@xxxxxxxxxx>

commit b76b46902c2d0395488c8412e1116c2486cdfcb2 upstream.

There is a recent report on UFFDIO_COPY over hugetlb:

https://lore.kernel.org/all/000000000000ee06de0616177560@xxxxxxxxxx/

350:	lockdep_assert_held(&hugetlb_lock);

Should be an issue in hugetlb but triggered in an userfault context, where
it goes into the unlikely path where two threads modifying the resv map
together.  Mike has a fix in that path for resv uncharge but it looks like
the locking criteria was overlooked: hugetlb_cgroup_uncharge_folio_rsvd()
will update the cgroup pointer, so it requires to be called with the lock
held.

Link: https://lkml.kernel.org/r/20240417211836.2742593-3-peterx@xxxxxxxxxx
Fixes: 79aa925bf239 ("hugetlb_cgroup: fix reservation accounting")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reported-by: syzbot+4b8077a5fccc61c385a1@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Mina Almasry <almasrymina@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/hugetlb.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3153,9 +3153,12 @@ struct folio *alloc_hugetlb_folio(struct
 
 		rsv_adjust = hugepage_subpool_put_pages(spool, 1);
 		hugetlb_acct_memory(h, -rsv_adjust);
-		if (deferred_reserve)
+		if (deferred_reserve) {
+			spin_lock_irq(&hugetlb_lock);
 			hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
 					pages_per_huge_page(h), folio);
+			spin_unlock_irq(&hugetlb_lock);
+		}
 	}
 	return folio;
 


Patches currently in stable-queue which might be from peterx@xxxxxxxxxx are

queue-6.6/mm-hugetlb-fix-missing-hugetlb_lock-for-resv-uncharge.patch




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