Commit 68f24b08ee89 ("sched/core: Free the stack early if CONFIG_THREAD_INFO_IN_TASK") may cause the task->stack to be freed during kmemleak_scan() execution, leading to either a NULL pointer fault (if task->stack is NULL) or kmemleak accessing already freed memory. This patch uses the new try_get_task_stack() API to ensure that the task stack is not freed during kmemleak stack scanning.
Fixes: 68f24b08ee89 ("sched/core: Free the stack early if CONFIG_THREAD_INFO_IN_TASK") Cc: Andrew Morton <a...@linux-foundation.org> Cc: Andy Lutomirski <l...@kernel.org> Cc: CAI Qian <caiq...@redhat.com> Reported-by: CAI Qian <caiq...@redhat.com> Signed-off-by: Catalin Marinas <catalin.mari...@arm.com> --- This was reported in a subsequent comment here: https://bugzilla.kernel.org/show_bug.cgi?id=173901 However, the original bugzilla entry doesn't look related to task stack freeing as it was first reported on 4.8-rc8. Andy, sorry for cc'ing you to bugzilla, please feel free to remove your email from the bug above (I can't seem to be able to do it). mm/kmemleak.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index a5e453cf05c4..e5355a5b423f 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1453,8 +1453,11 @@ static void kmemleak_scan(void) read_lock(&tasklist_lock); do_each_thread(g, p) { - scan_block(task_stack_page(p), task_stack_page(p) + - THREAD_SIZE, NULL); + void *stack = try_get_task_stack(p); + if (stack) { + scan_block(stack, stack + THREAD_SIZE, NULL); + put_task_stack(p); + } } while_each_thread(g, p); read_unlock(&tasklist_lock); }