From 65e722a74df992719676ead85a9e93fb2b5a0983 Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" Date: Mon, 19 Oct 2026 16:57:48 +0100 Subject: [PATCH] mm/mremap: correctly uncharge accountable VMAs in error path 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) Signed-off-by: Andrew Morton Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Jann Horn Cc: Pedro Falcato Cc: Brian Geffon Cc: Dmitry Safonov <0x7f454c46@gmail.com> Cc: --- mm/mremap.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/mremap.c b/mm/mremap.c index 24827e13e617..0d06d7f37f19 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -1339,6 +1339,20 @@ static int copy_vma_and_data(struct vma_remap_struct *vrm, 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;