On 9/7/21 22:05, Shuah Khan wrote: > 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. I think if this problem manifests only with CONFIG_PROVE_RAW_LOCK_NESTING then it shouldn't be backported to stable. CONFIG_PROVE_RAW_LOCK_NESTING is an experimental/development option to earlier discover what will collide with RT lock semantics, without needing the full RT tree. Thus, good to fix going forward, but not necessary to stable backport. > Here is my > > Tested-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx> > > thanks, > -- Shuah >
