On 29.11.22 20:35, Peter Xu wrote:
Since page_vma_mapped_walk() walks the pgtable, it needs the vma lock
to make sure the pgtable page will not be freed concurrently.
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
include/linux/rmap.h | 4 ++++
mm/page_vma_mapped.c | 5 ++++-
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index bd3504d11b15..a50d18bb86aa 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -13,6 +13,7 @@
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/memremap.h>
+#include <linux/hugetlb.h>
/*
* The anon_vma heads a list of private "related" vmas, to scan if
@@ -408,6 +409,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
pte_unmap(pvmw->pte);
if (pvmw->ptl)
spin_unlock(pvmw->ptl);
+ /* This needs to be after unlock of the spinlock */
+ if (is_vm_hugetlb_page(pvmw->vma))
+ hugetlb_vma_unlock_read(pvmw->vma);
}
bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 93e13fc17d3c..f94ec78b54ff 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -169,10 +169,13 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
if (pvmw->pte)
return not_found(pvmw);
+ hugetlb_vma_lock_read(vma);
/* when pud is not present, pte will be NULL */
pvmw->pte = huge_pte_offset(mm, pvmw->address, size);
- if (!pvmw->pte)
+ if (!pvmw->pte) {
+ hugetlb_vma_unlock_read(vma);
return false;
+ }
pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte);
if (!check_pte(pvmw))
Looking at code like mm/damon/paddr.c:__damon_pa_mkold() and reading
the doc of page_vma_mapped_walk(), this might be broken.
Can't we get page_vma_mapped_walk() called multiple times? Wouldn't we
have to remember that we already took the lock to not lock twice, and to
see if we really have to unlock in page_vma_mapped_walk_done() ?
--
Thanks,
David / dhildenb
