vm: fix move_vma() memory accounting being off

3cec5049 · Linus Torvalds <[email protected]> · 2023-09-16 12:31:42 -07:00

Commit 408579cd627a ("mm: Update do_vmi_align_munmap() return
semantics") seems to have updated one of the callers of do_vmi_munmap()
incorrectly: it used to check for the error case (which didn't
change: negative means error).

That commit changed the check to the success case (which did change:
before that commit, 0 was success, and 1 was "success and lock
downgraded".  After the change, it's always 0 for success, and the lock
will have been released if requested).

This didn't change any actual VM behavior _except_ for memory accounting
when 'VM_ACCOUNT' was set on the vma.  Which made the wrong return value
test fairly subtle, since everything continues to work.

Or rather - it continues to work but the "Committed memory" accounting
goes all wonky (Committed_AS value in /proc/meminfo), and depending on
settings that then causes problems much much later as the VM relies on
bogus statistics for its heuristics.

Revert that one line of the change back to the original logic.

Fixes: 408579cd627a ("mm: Update do_vmi_align_munmap() return semantics")
Reported-by: Christoph Biedl <[email protected]>
Reported-bisected-and-tested-by: Michael Labiuk <[email protected]>
Cc: Bagas Sanjaya <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 3cec50490969afd4a76ccee441f747d869ccff77
Parents: ad8a69f3

Changes

1 files changed · +1 −1

File	Status	Add	Del	Content
mm/mremap.c	modified	+1	−1	View file

mm/mremap.c

View file

diff --git a/mm/mremap.c b/mm/mremap.c
index 056478c..382e81c 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -715,7 +715,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	}
 
 	vma_iter_init(&vmi, mm, old_addr);
-	if (!do_vmi_munmap(&vmi, mm, old_addr, old_len, uf_unmap, false)) {
+	if (do_vmi_munmap(&vmi, mm, old_addr, old_len, uf_unmap, false) < 0) {
 		/* OOM: unable to split vma, just get accounts right */
 		if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP))
 			vm_acct_memory(old_len >> PAGE_SHIFT);