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

[Shuah Khan]

On 9/7/21 8:13 AM, Marco Elver 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@xxxxxxxxxxxxxxxxxxx
>
> 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
>
>   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(-)

Thank you. Tested all the 6 patches in this series on Linux 5.14. This problem
exists in 5.13 and needs to be marked for both 5.14 and 5.13 stable releases.

Here is my

Tested-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>

thanks,
-- Shuah