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

[Marco Elver]

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@xxxxxxxxxxxxxxxxxxx

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