| From: Hugh Dickins <hughd@google.com> |
| Subject: shmem: fix smaps BUG sleeping while atomic |
| Date: Tue, 22 Aug 2023 22:14:47 -0700 (PDT) |
| |
| smaps_pte_hole_lookup() is calling shmem_partial_swap_usage() with page |
| table lock held: but shmem_partial_swap_usage() does cond_resched_rcu() if |
| need_resched(): "BUG: sleeping function called from invalid context". |
| |
| Since shmem_partial_swap_usage() is designed to count across a range, but |
| smaps_pte_hole_lookup() only calls it for a single page slot, just break |
| out of the loop on the last or only page, before checking need_resched(). |
| |
| Link: https://lkml.kernel.org/r/6fe3b3ec-abdf-332f-5c23-6a3b3a3b11a9@google.com |
| Fixes: 230100321518 ("mm/smaps: simplify shmem handling of pte holes") |
| Signed-off-by: Hugh Dickins <hughd@google.com> |
| Acked-by: Peter Xu <peterx@redhat.com> |
| Cc: <stable@vger.kernel.org> [5.16+] |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| mm/shmem.c | 6 ++++-- |
| 1 file changed, 4 insertions(+), 2 deletions(-) |
| |
| --- a/mm/shmem.c~shmem-fix-smaps-bug-sleeping-while-atomic |
| +++ a/mm/shmem.c |
| @@ -806,14 +806,16 @@ unsigned long shmem_partial_swap_usage(s |
| XA_STATE(xas, &mapping->i_pages, start); |
| struct page *page; |
| unsigned long swapped = 0; |
| + unsigned long max = end - 1; |
| |
| rcu_read_lock(); |
| - xas_for_each(&xas, page, end - 1) { |
| + xas_for_each(&xas, page, max) { |
| if (xas_retry(&xas, page)) |
| continue; |
| if (xa_is_value(page)) |
| swapped++; |
| - |
| + if (xas.xa_index == max) |
| + break; |
| if (need_resched()) { |
| xas_pause(&xas); |
| cond_resched_rcu(); |
| _ |
