Re: [PATCH] mm: Fix mmap_assert_locked() in follow_pte()

Bert Karwatzki
2024-07-12T12:44:19Z

diff --git a/mm/memory.c b/mm/memory.c
index 282203363177..2f4b4322ec0e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1817,6 +1817,7 @@ static void unmap_single_vma(struct mmu_gather *tlb,
{
unsigned long start = max(vma->vm_start, start_addr);
unsigned long end;
+ bool mm_read_locked;

if (start >= vma->vm_end)
return;
@@ -1829,11 +1830,11 @@ static void unmap_single_vma(struct mmu_gather *tlb,

if (unlikely(vma->vm_flags & VM_PFNMAP)) {
if (!mm_wr_locked)
- mmap_read_lock(vma->vm_mm);
+ mm_read_locked = !mmap_read_trylock(vma->vm_mm);

untrack_pfn(vma, 0, 0, mm_wr_locked);

- if (!mm_wr_locked)
+ if (!mm_wr_locked && !mm_read_locked)
mmap_read_unlock(vma->vm_mm);
}

This seems to fix the issue without completely removing the locking.

Bert Karwatzki