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

* + hugetlb-userfaultfd-fix-reservation-restore-on-userfaultfd-error.patch added to -mm tree
@ 2021-11-18 22:04 akpm
  0 siblings, 0 replies; 3+ messages in thread
From: akpm @ 2021-11-18 22:04 UTC (permalink / raw)
  To: almasrymina, jthoughton, mm-commits, stable, weixugc


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 <almasrymina@google.com>
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().  Rename new_pagecache_page to
page_in_pagecache to make that clear.

Link: https://lkml.kernel.org/r/20211117193825.378528-1-almasrymina@google.com
Fixes: c7b1850dfb41 ("hugetlb: don't pass page cache pages to restore_reserve_on_error")
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reported-by: James Houghton <jthoughton@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/mm/hugetlb.c~hugetlb-userfaultfd-fix-reservation-restore-on-userfaultfd-error
+++ a/mm/hugetlb.c
@@ -5734,13 +5734,14 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 	int ret = -ENOMEM;
 	struct page *page;
 	int writable;
-	bool new_pagecache_page = false;
+	bool page_in_pagecache = false;
 
 	if (is_continue) {
 		ret = -EFAULT;
 		page = find_lock_page(mapping, idx);
 		if (!page)
 			goto out;
+		page_in_pagecache = true;
 	} else if (!*pagep) {
 		/* If a page already exists, then it's UFFDIO_COPY for
 		 * a non-missing case. Return -EEXIST.
@@ -5828,7 +5829,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 		ret = huge_add_to_page_cache(page, mapping, idx);
 		if (ret)
 			goto out_release_nounlock;
-		new_pagecache_page = true;
+		page_in_pagecache = true;
 	}
 
 	ptl = huge_pte_lockptr(h, dst_mm, dst_pte);
@@ -5892,7 +5893,7 @@ out_release_unlock:
 	if (vm_shared || is_continue)
 		unlock_page(page);
 out_release_nounlock:
-	if (!new_pagecache_page)
+	if (!page_in_pagecache)
 		restore_reserve_on_error(h, dst_vma, dst_addr, page);
 	put_page(page);
 	goto out;
_

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

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


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