[merged mm-stable] mm-mremap-correctly-uncharge-accountable-vmas-in-error-path.patch removed from -mm tree

[merged mm-stable] mm-mremap-correctly-uncharge-accountable-vmas-in-error-path.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/mremap: correctly uncharge accountable VMAs in error path
has been removed from the -mm tree.  Its filename was
     mm-mremap-correctly-uncharge-accountable-vmas-in-error-path.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/mremap: correctly uncharge accountable VMAs in error path
Date: Mon, 19 Oct 2026 16:57:48 +0100

The mremap error path is a fragile and unwieldy beast - it reverses the
page table move then updates vma_remap_struct state to swap VMA, length and
address between old and new VMAs in copy_vma_and_data().

If the mremap() operation didn't specify MREMAP_DONTUNMAP then its caller,
move_vma(), invokes unmap_source_vma(), which unmaps the new VMA rather
than the old one.

For accountable VMAs when MREMAP_DONTUNMAP is not specified,
unmap_source_vma() unsets VMA_ACCOUNT_BIT during this unmap in order that
only the delta of a VMA expansion is charged (performed by
vrm_calc_charge() earlier).

Therefore nothing uncharges the expanded VMA size, and there is a permanent
leak in global Committed_AS.

Resolve the issue by uncharging when MREMAP_DONTUNMAP is not specified.

Link: https://lore.kernel.org/20261019-other-mremap-charge-leak-v1-1-d94477fe6545@kernel.org
Fixes: fdbef6149135 ("mm/mremap: don't account pages in vma_to_resize()")
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: <stable@vger.kernel.org>
---

 mm/mremap.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/mm/mremap.c~mm-mremap-correctly-uncharge-accountable-vmas-in-error-path
+++ a/mm/mremap.c
@@ -1339,6 +1339,20 @@ static int copy_vma_and_data(struct vma_
 		pmc_revert.need_rmap_locks = true;
 		move_page_tables(&pmc_revert);
 
+		/*
+		 * When copy_vma_and_data() returns, the new VMA will be
+		 * unmapped rather than the old one.
+		 *
+		 * When an accountable move is being performed, this unmapping
+		 * will not uncharge any expansion, so do that now.
+		 *
+		 * A move is accountable if the VMA is accountable and
+		 * MREMAP_DONTUNMAP is not specified, so only do so if the
+		 * latter is true.
+		 */
+		if (!(vrm->flags & MREMAP_DONTUNMAP))
+			vrm_uncharge(vrm);
+
 		vrm->vma = new_vma;
 		vrm->old_len = vrm->new_len;
 		vrm->addr = vrm->new_addr;
_

Patches currently in -mm which might be from ljs@kernel.org are

mm-vma-fix-expansion-of-vma_mixedmap_bit-vmas.patch
mm-do-not-unintentionally-overwrite-atomic-vma-flags.patch
mm-vma-avoid-losing-atomic-vma-flags-when-setting-sticky-vma-flags.patch