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sched/core: Disable page allocation in task_tick_mm_cid()

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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 223baf9d17 ("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: 223baf9d17 ("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
This commit is contained in:
Waiman Long 2024-10-09 21:44:32 -04:00 committed by Peter Zijlstra
parent d16b7eb6f5
commit 73ab05aa46
3 changed files with 20 additions and 4 deletions
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5
include/linux/task_work.h
View File

@ -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)

4
kernel/sched/core.c
View File

@ -10458,7 +10458,9 @@ void task_tick_mm_cid(struct rq *rq, struct task_struct *curr)
return;
if (time_before(now, READ_ONCE(curr->mm->mm_cid_next_scan)))
return;
task_work_add(curr, work, TWA_RESUME);
/* No page allocation under rq lock */
task_work_add(curr, work, TWA_RESUME | TWAF_NO_ALLOC);
}
void sched_mm_cid_exit_signals(struct task_struct *t)

13
kernel/task_work.c
View File

@ -55,14 +55,25 @@ 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 */
/*
* 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);
}