sched/core: Disable page allocation in task_tick_mm_cid()

[ Upstream commit 73ab05aa46b02d96509cb029a8d04fca7bbde8c7 ]

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 <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20241010014432.194742-1-longman@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index cf5e7e891a77..2964171856e0 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -14,11 +14,14 @@ init_task_work(struct callback_head *twork, task_work_func_t func)
 }
 
 enum task_work_notify_mode {
-	TWA_NONE,
+	TWA_NONE = 0,
 	TWA_RESUME,
 	TWA_SIGNAL,
 	TWA_SIGNAL_NO_IPI,
 	TWA_NMI_CURRENT,
+
+	TWA_FLAGS = 0xff00,
+	TWAF_NO_ALLOC = 0x0100,
 };
 
 static inline bool task_work_pending(struct task_struct *task)