+ mm-swapfile-make-security_vm_enough_memory_mm-work-as-expected.patch added to mm-unstable branch

+ mm-swapfile-make-security_vm_enough_memory_mm-work-as-expected.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/swapfile: make security_vm_enough_memory_mm() work as expected
has been added to the -mm mm-unstable branch.  Its filename is
     mm-swapfile-make-security_vm_enough_memory_mm-work-as-expected.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swapfile-make-security_vm_enough_memory_mm-work-as-expected.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Miaohe Lin <linmiaohe@huawei.com>
Subject: mm/swapfile: make security_vm_enough_memory_mm() work as expected
Date: Wed, 8 Jun 2022 22:40:29 +0800

Patch series "A few cleanup and fixup patches for swap", v2.

This series contains a cleaup patch to remove unneeded swap_cache_info
statistics, and two bugfix patches to avoid possible data races of
inuse_pages and so on.  More details can be found in the respective
changelogs.


This patch (of 3):

security_vm_enough_memory_mm() checks whether a process has enough memory
to allocate a new virtual mapping.  And total_swap_pages is considered as
available memory while swapoff tries to make sure there's enough memory
that can hold the swapped out memory.  But total_swap_pages contains the
swap space that is being swapoff.  So security_vm_enough_memory_mm() will
success even if there's no memory to hold the swapped out memory because
total_swap_pages always greater than or equal to p->pages.

In order to fix it, p->pages should be subtracted from total_swap_pages
first and then check whether there's enough memory for inuse swap pages.

Link: https://lkml.kernel.org/r/20220608144031.829-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20220608144031.829-2-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/swapfile.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/mm/swapfile.c~mm-swapfile-make-security_vm_enough_memory_mm-work-as-expected
+++ a/mm/swapfile.c
@@ -2398,6 +2398,7 @@ SYSCALL_DEFINE1(swapoff, const char __us
 	struct filename *pathname;
 	int err, found = 0;
 	unsigned int old_block_size;
+	unsigned int inuse_pages;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -2428,9 +2429,13 @@ SYSCALL_DEFINE1(swapoff, const char __us
 		spin_unlock(&swap_lock);
 		goto out_dput;
 	}
-	if (!security_vm_enough_memory_mm(current->mm, p->pages))
-		vm_unacct_memory(p->pages);
+
+	total_swap_pages -= p->pages;
+	inuse_pages = READ_ONCE(p->inuse_pages);
+	if (!security_vm_enough_memory_mm(current->mm, inuse_pages))
+		vm_unacct_memory(inuse_pages);
 	else {
+		total_swap_pages += p->pages;
 		err = -ENOMEM;
 		spin_unlock(&swap_lock);
 		goto out_dput;
@@ -2453,7 +2458,6 @@ SYSCALL_DEFINE1(swapoff, const char __us
 	}
 	plist_del(&p->list, &swap_active_head);
 	atomic_long_sub(p->pages, &nr_swap_pages);
-	total_swap_pages -= p->pages;
 	p->flags &= ~SWP_WRITEOK;
 	spin_unlock(&p->lock);
 	spin_unlock(&swap_lock);
_

Patches currently in -mm which might be from linmiaohe@huawei.com are

maintainers-add-myself-as-a-memory-failure-reviewer.patch
mm-shmemc-clean-up-comment-of-shmem_swapin_folio.patch
mm-reduce-the-rcu-lock-duration.patch
mm-migration-remove-unneeded-lock-page-and-pagemovable-check.patch
mm-migration-return-errno-when-isolate_huge_page-failed.patch
mm-migration-fix-potential-pte_unmap-on-an-not-mapped-pte.patch
mm-memremap-fix-wrong-function-name-above-memremap_pages.patch
mm-swapfile-make-security_vm_enough_memory_mm-work-as-expected.patch
mm-swapfile-fix-possible-data-races-of-inuse_pages.patch
mm-swap-remove-swap_cache_info-statistics.patch
mm-vmscan-dont-try-to-reclaim-freed-folios.patch
lib-test_hmm-avoid-accessing-uninitialized-pages.patch
mm-memremap-fix-memunmap_pages-race-with-get_dev_pagemap.patch
mm-khugepaged-remove-unneeded-shmem_huge_enabled-check.patch
mm-khugepaged-stop-swapping-in-page-when-vm_fault_retry-occurs.patch
mm-khugepaged-trivial-typo-and-codestyle-cleanup.patch
mm-khugepaged-minor-cleanup-for-collapse_file.patch
mm-khugepaged-use-helper-macro-__attr_rw.patch
mm-khugepaged-remove-unneeded-return-value-of-khugepaged_add_pte_mapped_thp.patch
mm-khugepaged-try-to-free-transhuge-swapcache-when-possible.patch
mm-page_alloc-minor-clean-up-for-memmap_init_compound.patch