Re: [PATCH 0/6] stackdepot, kasan, workqueue: Avoid expanding stackdepot slabs when holding raw_spin_lock

[Alexander Potapenko <glider@google.com>]

On Tue, Sep 7, 2021 at 4:14 PM Marco Elver <elver@google.com> wrote:
>
> Shuah Khan reported [1]:
>
>  | When CONFIG_PROVE_RAW_LOCK_NESTING=y and CONFIG_KASAN are enabled,
>  | kasan_record_aux_stack() runs into "BUG: Invalid wait context" when
>  | it tries to allocate memory attempting to acquire spinlock in page
>  | allocation code while holding workqueue pool raw_spinlock.
>  |
>  | There are several instances of this problem when block layer tries
>  | to __queue_work(). Call trace from one of these instances is below:
>  |
>  |     kblockd_mod_delayed_work_on()
>  |       mod_delayed_work_on()
>  |         __queue_delayed_work()
>  |           __queue_work() (rcu_read_lock, raw_spin_lock pool->lock held)
>  |             insert_work()
>  |               kasan_record_aux_stack()
>  |                 kasan_save_stack()
>  |                   stack_depot_save()
>  |                     alloc_pages()
>  |                       __alloc_pages()
>  |                         get_page_from_freelist()
>  |                           rm_queue()
>  |                             rm_queue_pcplist()
>  |                               local_lock_irqsave(&pagesets.lock, flags);
>  |                               [ BUG: Invalid wait context triggered ]
>
> [1] https://lkml.kernel.org/r/20210902200134.25603-1-skhan@linuxfoundation.org
>
> PROVE_RAW_LOCK_NESTING is pointing out that (on RT kernels) the locking
> rules are being violated. More generally, memory is being allocated from
> a non-preemptive context (raw_spin_lock'd c-s) where it is not allowed.
>
> To properly fix this, we must prevent stackdepot from replenishing its
> "stack slab" pool if memory allocations cannot be done in the current
> context: it's a bug to use either GFP_ATOMIC nor GFP_NOWAIT in certain
> non-preemptive contexts, including raw_spin_locks (see gfp.h and
> ab00db216c9c7).
>
> The only downside is that saving a stack trace may fail if: stackdepot
> runs out of space AND the same stack trace has not been recorded before.
> I expect this to be unlikely, and a simple experiment (boot the kernel)
> didn't result in any failure to record stack trace from insert_work().
>
> The series includes a few minor fixes to stackdepot that I noticed in
> preparing the series. It then introduces __stack_depot_save(), which
> exposes the option to force stackdepot to not allocate any memory.
> Finally, KASAN is changed to use the new stackdepot interface and
> provide kasan_record_aux_stack_noalloc(), which is then used by
> workqueue code.
>
> Marco Elver (6):
>   lib/stackdepot: include gfp.h
>   lib/stackdepot: remove unused function argument
>   lib/stackdepot: introduce __stack_depot_save()
>   kasan: common: provide can_alloc in kasan_save_stack()
>   kasan: generic: introduce kasan_record_aux_stack_noalloc()
>   workqueue, kasan: avoid alloc_pages() when recording stack

Acked-by: Alexander Potapenko <glider@google.com>

for the whole series.

>
>  include/linux/kasan.h      |  2 ++
>  include/linux/stackdepot.h |  6 +++++
>  kernel/workqueue.c         |  2 +-
>  lib/stackdepot.c           | 51 ++++++++++++++++++++++++++++++--------
>  mm/kasan/common.c          |  6 ++---
>  mm/kasan/generic.c         | 14 +++++++++--
>  mm/kasan/kasan.h           |  2 +-
>  7 files changed, 65 insertions(+), 18 deletions(-)
>
> --
> 2.33.0.153.gba50c8fa24-goog
>


-- 
Alexander Potapenko
Software Engineer

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