From 73ab05aa46b02d96509cb029a8d04fca7bbde8c7 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Wed, 9 Oct 2024 21:44:32 -0400 Subject: sched/core: Disable page allocation in task_tick_mm_cid() With KASAN and PREEMPT_RT enabled, calling task_work_add() in task_tick_mm_cid() may cause the following splat. [ 63.696416] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48 [ 63.696416] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 610, name: modprobe [ 63.696416] preempt_count: 10001, expected: 0 [ 63.696416] RCU nest depth: 1, expected: 1 This problem is caused by the following call trace. sched_tick() [ acquire rq->__lock ] -> task_tick_mm_cid() -> task_work_add() -> __kasan_record_aux_stack() -> kasan_save_stack() -> stack_depot_save_flags() -> alloc_pages_mpol_noprof() -> __alloc_pages_noprof() -> get_page_from_freelist() -> rmqueue() -> rmqueue_pcplist() -> __rmqueue_pcplist() -> rmqueue_bulk() -> rt_spin_lock() The rq lock is a raw_spinlock_t. We can't sleep while holding it. IOW, we can't call alloc_pages() in stack_depot_save_flags(). The task_tick_mm_cid() function with its task_work_add() call was introduced by commit 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid") in v6.4 kernel. Fortunately, there is a kasan_record_aux_stack_noalloc() variant that calls stack_depot_save_flags() while not allowing it to allocate new pages. To allow task_tick_mm_cid() to use task_work without page allocation, a new TWAF_NO_ALLOC flag is added to enable calling kasan_record_aux_stack_noalloc() instead of kasan_record_aux_stack() if set. The task_tick_mm_cid() function is modified to add this new flag. The possible downside is the missing stack trace in a KASAN report due to new page allocation required when task_work_add_noallloc() is called which should be rare. Fixes: 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid") Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20241010014432.194742-1-longman@redhat.com --- kernel/task_work.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) (limited to 'kernel/task_work.c') diff --git a/kernel/task_work.c b/kernel/task_work.c index 5d14d639ac71..c969f1f26be5 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -55,15 +55,26 @@ int task_work_add(struct task_struct *task, struct callback_head *work, enum task_work_notify_mode notify) { struct callback_head *head; + int flags = notify & TWA_FLAGS; + notify &= ~TWA_FLAGS; if (notify == TWA_NMI_CURRENT) { if (WARN_ON_ONCE(task != current)) return -EINVAL; if (!IS_ENABLED(CONFIG_IRQ_WORK)) return -EINVAL; } else { - /* record the work call stack in order to print it in KASAN reports */ - kasan_record_aux_stack(work); + /* + * Record the work call stack in order to print it in KASAN + * reports. + * + * Note that stack allocation can fail if TWAF_NO_ALLOC flag + * is set and new page is needed to expand the stack buffer. + */ + if (flags & TWAF_NO_ALLOC) + kasan_record_aux_stack_noalloc(work); + else + kasan_record_aux_stack(work); } head = READ_ONCE(task->task_works); -- cgit