Re: [PATCH v2 0/6] stackdepot, kasan, workqueue: Avoid expanding stackdepot slabs when holding raw_spin_lock

Andrey Konovalov
2021-10-03T17:53:28Z

On Mon, Sep 13, 2021 at 1:26 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 ]
>
> 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.
>
> [1] https://lkml.kernel.org/r/20210902200134.25603-1-skhan@linuxfoundation.org
>
> v2:
> * Refer to __stack_depot_save() in comment of stack_depot_save().
>
> 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 | 52 ++++++++++++++++++++++++++++++--------
> mm/kasan/common.c | 6 ++---
> mm/kasan/generic.c | 14 ++++++++--
> mm/kasan/kasan.h | 2 +-
> 7 files changed, 66 insertions(+), 18 deletions(-)
>
> --
> 2.33.0.309.g3052b89438-goog
>

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>

for the series.