Messages in this thread | | | From | Marco Elver <> | Date | Thu, 2 Sep 2021 23:58:12 +0200 | Subject | Re: [PATCH v2] workqueue: Don't record workqueue stack holding raw_spin_lock |
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On Thu, 2 Sept 2021 at 22:01, Shuah Khan <skhan@linuxfoundation.org> wrote: > > 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 ] > > Fix it by calling kasan_record_aux_stack() conditionally only when > CONFIG_PROVE_RAW_LOCK_NESTING is not enabled. After exploring other > options such as calling kasan_record_aux_stack() after releasing the > pool lock, opting for a least disruptive path of stubbing this record > function to avoid nesting raw spinlock and spinlock. > > ============================= > [ BUG: Invalid wait context ] > 5.14.0-rc7+ #8 Not tainted > ----------------------------- > snap/532 is trying to lock: > ffff888374f32ba0 (lock#2){..-.}-{3:3}, at: get_page_from_freelist (mm/page_alloc.c:3665 mm/page_alloc.c:3703 mm/page_alloc.c:4165) > other info that might help us debug this: > context-{5:5} > 3 locks held by snap/532: > #0: ffff888139fa4408 (&type->i_mutex_dir_key#10){.+.+}-{4:4}, at: walk_component (fs/namei.c:1663 fs/namei.c:1959) > #1: ffffffffab870c40 (rcu_read_lock){....}-{1:3}, at: __queue_work (./arch/x86/include/asm/preempt.h:80 ./include/linux/rcupdate.h:68 ./include/linux/rcupdate.h:685 kernel/workqueue.c:1421) > #2: ffff888374f36cd8 (&pool->lock){-.-.}-{2:2}, at: __queue_work (kernel/workqueue.c:1466) > stack backtrace: > CPU: 14 PID: 532 Comm: snap Not tainted 5.14.0-rc7+ #8 > Hardware name: LENOVO 90Q30008US/3728, BIOS O4ZKT1CA 09/16/2020 > Call Trace: > dump_stack_lvl (lib/dump_stack.c:106 (discriminator 4)) > dump_stack (lib/dump_stack.c:113) > __lock_acquire.cold (kernel/locking/lockdep.c:4666 kernel/locking/lockdep.c:4727 kernel/locking/lockdep.c:4965) > ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4873) > ? lock_is_held_type (kernel/locking/lockdep.c:5368 kernel/locking/lockdep.c:5668) > lock_acquire (kernel/locking/lockdep.c:438 kernel/locking/lockdep.c:5627 kernel/locking/lockdep.c:5590) > ? get_page_from_freelist (mm/page_alloc.c:3665 mm/page_alloc.c:3703 mm/page_alloc.c:4165) > ? lock_release (kernel/locking/lockdep.c:5593) > ? __kasan_check_read (mm/kasan/shadow.c:32) > ? __lock_acquire (kernel/locking/lockdep.c:5019) > ? __zone_watermark_ok (./include/linux/list.h:282 ./include/linux/mmzone.h:111 mm/page_alloc.c:3908) > get_page_from_freelist (./include/linux/local_lock_internal.h:43 mm/page_alloc.c:3665 mm/page_alloc.c:3703 mm/page_alloc.c:4165) > ? get_page_from_freelist (mm/page_alloc.c:3665 mm/page_alloc.c:3703 mm/page_alloc.c:4165) > ? lock_is_held_type (kernel/locking/lockdep.c:5368 kernel/locking/lockdep.c:5668) > ? is_bpf_text_address (./arch/x86/include/asm/preempt.h:85 ./include/linux/rcupdate.h:73 ./include/linux/rcupdate.h:719 kernel/bpf/core.c:708) > ? lock_downgrade (kernel/locking/lockdep.c:5633) > ? __zone_watermark_ok (mm/page_alloc.c:4054) > __alloc_pages (mm/page_alloc.c:5391) > ? __alloc_pages_slowpath.constprop.0 (mm/page_alloc.c:5354) > ? create_prof_cpu_mask (kernel/stacktrace.c:82) > ? _find_first_bit (lib/find_bit.c:83) > alloc_pages (mm/mempolicy.c:2249) > stack_depot_save (lib/stackdepot.c:304) > ? lock_is_held_type (kernel/locking/lockdep.c:5368 kernel/locking/lockdep.c:5668) > kasan_save_stack (mm/kasan/common.c:41) > ? kasan_save_stack (mm/kasan/common.c:39) > ? kasan_record_aux_stack (mm/kasan/generic.c:348) > ? insert_work (./include/linux/instrumented.h:71 ./include/asm-generic/bitops/instrumented-non-atomic.h:134 kernel/workqueue.c:616 kernel/workqueue.c:623 kernel/workqueue.c:1335) > ? __queue_work (kernel/workqueue.c:1501) > ? __queue_delayed_work (kernel/workqueue.c:1657) > ? mod_delayed_work_on (kernel/workqueue.c:1720) > ? kblockd_mod_delayed_work_on (block/blk-core.c:1633) > ? __blk_mq_delay_run_hw_queue (block/blk-mq.c:1567) > ? blk_mq_run_hw_queue (block/blk-mq.c:1610) > ? blk_mq_sched_insert_request (block/blk-mq-sched.c:480) > ? blk_mq_submit_bio (block/blk-mq.c:2276) > > Fixes: e89a85d63fb2 ("workqueue: kasan: record workqueue stack") > Signed-off-by: Shuah Khan <skhan@linuxfoundation.org> > --- > Changes since v1: > -- Instead of changing when record happens, disable record > when CONFIG_PROVE_RAW_LOCK_NESTING=y > > kernel/workqueue.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index f148eacda55a..435970ef81ae 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -1328,8 +1328,16 @@ static void insert_work(struct pool_workqueue *pwq, struct work_struct *work, > { > struct worker_pool *pool = pwq->pool; > > - /* record the work call stack in order to print it in KASAN reports */ > + /* > + * record the work call stack in order to print it in KASAN reports > + * Doing this when CONFIG_PROVE_RAW_LOCK_NESTING is enabled results > + * in nesting raw spinlock with page allocation spinlock. > + * > + * Avoid recording when CONFIG_PROVE_RAW_LOCK_NESTING is enabled. > + */ > +#if !defined(CONFIG_PROVE_RAW_LOCK_NESTING)
Just "if (!IS_ENABLED(CONFIG_PROVE_RAW_LOCK_NESTING))" should work here, however...
... PROVE_RAW_LOCK_NESTING exists for PREEMPT_RT's benefit. I don't think silencing the debugging tool is the solution, because the bug still exists in a PREEMPT_RT kernel.
+Cc Sebastian for advice. I may have missed something obvious. :-)
I have a suspicion that kasan_record_aux_stack() (via stack_depot_save()) is generally unsound on PREEMPT_RT kernels, because allocating memory cannot be done within raw-locked critical sections because memory allocation is preemptible on RT. Even using GWP_NOWAIT/ATOMIC doesn't help (which kasan_record_aux_stack() uses).
It follows that if we do not know what type of locks may be held when calling kasan_record_aux_stack() we have a bug in RT.
I see 3 options:
1. Try to move kasan_record_aux_stack() where no raw lock is held. (Seems complicated per v1 attempt?)
But ideally we make kasan_record_aux_stack() more robust on RT:
2. Make kasan_record_aux_stack() a no-op on RT (and if PROVE_RAW_LOCK_NESTING). Perhaps overkill?
3. Try to not allocate memory in stackdepot. Not sure this is feasible without telling stackdepot to preallocate the max slabs on boot if RT.
Anything else? Because I don't think any of the options are satisfying.
Thanks, -- Marco
> kasan_record_aux_stack(work); > +#endif > > /* we own @work, set data and link */ > set_work_pwq(work, pwq, extra_flags); > -- > 2.30.2 >
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