diff options
| author | SeongJae Park <sj@kernel.org> | 2025-09-29 17:44:09 -0700 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-10-07 14:01:12 -0700 |
| commit | b93af2cc8e036754c0d9970d9ddc47f43cc94b9f (patch) | |
| tree | 54c50ec8e45ab23f41404cfbddcfa3f5d899c4e7 | |
| parent | 9658d698a8a83540bf6a6c80d13c9a61590ee985 (diff) | |
mm/damon/vaddr: do not repeat pte_offset_map_lock() until success
DAMON's virtual address space operation set implementation (vaddr) calls
pte_offset_map_lock() inside the page table walk callback function. This
is for reading and writing page table accessed bits. If
pte_offset_map_lock() fails, it retries by returning the page table walk
callback function with ACTION_AGAIN.
pte_offset_map_lock() can continuously fail if the target is a pmd
migration entry, though. Hence it could cause an infinite page table walk
if the migration cannot be done until the page table walk is finished.
This indeed caused a soft lockup when CPU hotplugging and DAMON were
running in parallel.
Avoid the infinite loop by simply not retrying the page table walk. DAMON
is promising only a best-effort accuracy, so missing access to such pages
is no problem.
Link: https://lkml.kernel.org/r/20250930004410.55228-1-sj@kernel.org
Fixes: 7780d04046a2 ("mm/pagewalkers: ACTION_AGAIN if pte_offset_map_lock() fails")
Signed-off-by: SeongJae Park <sj@kernel.org>
Reported-by: Xinyu Zheng <zhengxinyu6@huawei.com>
Closes: https://lore.kernel.org/20250918030029.2652607-1-zhengxinyu6@huawei.com
Acked-by: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org> [6.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | mm/damon/vaddr.c | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index 8c048f9b129e..7e834467b2d8 100644 --- a/mm/damon/vaddr.c +++ b/mm/damon/vaddr.c @@ -328,10 +328,8 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr, } pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); - if (!pte) { - walk->action = ACTION_AGAIN; + if (!pte) return 0; - } if (!pte_present(ptep_get(pte))) goto out; damon_ptep_mkold(pte, walk->vma, addr); @@ -481,10 +479,8 @@ regular_page: #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); - if (!pte) { - walk->action = ACTION_AGAIN; + if (!pte) return 0; - } ptent = ptep_get(pte); if (!pte_present(ptent)) goto out; |