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
