+ hugetlb-userfaultfd-fix-reservation-restore-on-userfaultfd-error.patch added to -mm tree

The patch titled
     Subject: hugetlb, userfaultfd: fix reservation restore on userfaultfd error
has been added to the -mm tree.  Its filename is
     hugetlb-userfaultfd-fix-reservation-restore-on-userfaultfd-error.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/hugetlb-userfaultfd-fix-reservation-restore-on-userfaultfd-error.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/hugetlb-userfaultfd-fix-reservation-restore-on-userfaultfd-error.patch

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------------------------------------------------------
From: Mina Almasry <redacted>
Subject: hugetlb, userfaultfd: fix reservation restore on userfaultfd error

Currently in the is_continue case in hugetlb_mcopy_atomic_pte(), if we
bail out using "goto out_release_unlock;" in the cases where idx >= size,
or !huge_pte_none(), the code will detect that new_pagecache_page ==
false, and so call restore_reserve_on_error().  In this case I see
restore_reserve_on_error() delete the reservation, and the following call
to remove_inode_hugepages() will increment h->resv_hugepages causing a
100% reproducible leak.

We should treat the is_continue case similar to adding a page into the
pagecache and set new_pagecache_page to true, to indicate that there is no
reservation to restore on the error path, and we need not call
restore_reserve_on_error().

Link: https://lkml.kernel.org/r/20211116235733.3774702-1-almasrymina@google.com
Fixes: c7b1850dfb41 ("hugetlb: don't pass page cache pages to restore_reserve_on_error")
Signed-off-by: Mina Almasry <redacted>
Reported-by: James Houghton <redacted>
Cc: Wei Xu <weixugc@google.com>
Cc: Mike Kravetz <redacted>
Cc: <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/mm/hugetlb.c~hugetlb-userfaultfd-fix-reservation-restore-on-userfaultfd-error
+++ a/mm/hugetlb.c

@@ -5743,6 +5743,14 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 		page = find_lock_page(mapping, idx);
 		if (!page)
 			goto out;
+		/*
+		 * Set new_pagecache_page to true, as we've added a page to the
+		 * pagecache, but userfaultfd hasn't set up a mapping for this
+		 * page yet. If we bail out before setting up the mapping, we
+		 * want to indicate to restore_reserve_on_error() that we've
+		 * added the page to the page cache.
+		 */
+		new_pagecache_page = true;
 	} else if (!*pagep) {
 		/* If a page already exists, then it's UFFDIO_COPY for
 		 * a non-missing case. Return -EEXIST.

_

Patches currently in -mm which might be from almasrymina@google.com are

hugetlb-userfaultfd-fix-reservation-restore-on-userfaultfd-error.patch