On Wed, Aug 16, 2023 at 08:25:49AM -0400, Joel Fernandes wrote:
> > On Aug 16, 2023, at 5:30 AM, Z qiang <qiang.zhang1211@xxxxxxxxx> wrote:
> >>>> On Tue, Aug 15, 2023 at 1:44 AM Z qiang <qiang.zhang1211@xxxxxxxxx> wrote:
> >>>>>
> >>>>> Hello, Paul
> >>>>>
> >>>>> when running the rcutorture test with rcutorture.object_debug=1 in
> >>>>> PREEMPT_RT kernel.
> >>>>>
> >>>>> BUG: sleeping function called from invalid context at
> >>>>> kernel/locking/spinlock_rt.c:48
> >>>>> [ 3.116503] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid:
> >>>>> 1, name: swapper/0
> >>>>> [ 3.116503] preempt_count: 1, expected: 0
> >>>>> [ 3.116503] RCU nest depth: 1, expected: 1
> >>>>> [ 3.116503] 3 locks held by swapper/0/1:
> >>>>> [ 3.116503] #0: ffffffff8f862d80 (fullstop_mutex){+.+.}-{4:4}, at:
> >>>>> torture_init_begin+0x24/0xa0
> >>>>> [ 3.116503] #1: ffffffff8f7b1400 (rcu_read_lock){....}-{1:3}, at:
> >>>>> rcu_torture_init+0x20b9/0x2380
> >>>>> [ 3.116503] #2: ffffffff8f89fa20 (vmap_area_lock){+.+.}-{3:3}, at:
> >>>>> find_vmap_area+0x21/0x90
> >>>>> [ 3.116503] irq event stamp: 571506
> >>>>> [ 3.116503] hardirqs last enabled at (571505):
> >>>>> [<ffffffff8d422ff5>] __call_rcu_common+0x3a5/0xdc0
> >>>>> [ 3.116503] hardirqs last disabled at (571506):
> >>>>> [<ffffffff900487f7>] rcu_torture_init+0x22b7/0x2380
> >>>>> [ 3.116503] softirqs last enabled at (406916):
> >>>>> [<ffffffff8d2e91f2>] __local_bh_enable_ip+0x132/0x170
> >>>>> [ 3.116503] softirqs last disabled at (406910):
> >>>>> [<ffffffff8e658e79>] inet_register_protosw+0x9/0x190
> >>>>> [ 3.116503] Preemption disabled at:
> >>>>> [ 3.116503] [<ffffffff9004865a>] rcu_torture_init+0x211a/0x2380
> >>>>> [ 3.116503] CPU: 2 PID: 1 Comm: swapper/0 Tainted: G W
> >>>>> 6.5.0-rc4-rt2-yocto-preempt-rt+ #7
> >>>>> [ 3.116503] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
> >>>>> BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014
> >>>>> [ 3.116503] Call Trace:
> >>>>> [ 3.116503] <TASK>
> >>>>> [ 3.116503] dump_stack_lvl+0x68/0xb0
> >>>>> [ 3.116503] dump_stack+0x14/0x20
> >>>>> [ 3.116503] __might_resched+0x221/0x2f0
> >>>>> [ 3.116503] rt_spin_lock+0x60/0x130
> >>>>> [ 3.116503] ? find_vmap_area+0x21/0x90
> >>>>> [ 3.116503] find_vmap_area+0x21/0x90
> >>>>> [ 3.116503] vmalloc_dump_obj+0x25/0xa0
> >>>>> [ 3.116503] mem_dump_obj+0x22/0x90
> >>>>> [ 3.116503] __call_rcu_common+0x920/0xdc0
> >>>>> [ 3.116503] ? __pfx_rcu_torture_err_cb+0x10/0x10
> >>>>> [ 3.116503] ? __pfx___call_rcu_common+0x10/0x10
> >>>>> [ 3.116503] ? rcu_torture_init+0x22b7/0x2380
> >>>>> [ 3.116503] ? debug_smp_processor_id+0x1b/0x30
> >>>>> [ 3.116503] ? rcu_is_watching+0x3e/0xc0
> >>>>> [ 3.116503] call_rcu_hurry+0x14/0x20
> >>>>> [ 3.116503] rcu_torture_init+0x2186/0x2380
> >>>>> [ 3.116503] ? __pfx_rcu_torture_init+0x10/0x10
> >>>>> [ 3.116503] ? __pfx_rt_mutex_slowunlock+0x10/0x10
> >>>>> [ 3.116503] ? __pfx_irq_debugfs_init+0x10/0x10
> >>>>> [ 3.116503] ? __pfx_rcu_torture_leak_cb+0x10/0x10
> >>>>> [ 3.116503] ? rt_spin_unlock+0x50/0xa0
> >>>>> [ 3.116503] ? add_device_randomness+0xb1/0xe0
> >>>>> [ 3.116503] ? __pfx_rcu_torture_leak_cb+0x10/0x10
> >>>>> [ 3.116503] ? __pfx_rcu_torture_init+0x10/0x10
> >>>>> [ 3.116503] do_one_initcall+0xd8/0x430
> >>>>> [ 3.116503] ? __pfx_do_one_initcall+0x10/0x10
> >>>>> [ 3.116503] ? __kasan_check_read+0x15/0x20
> >>>>> [ 3.116503] kernel_init_freeable+0x3a0/0x670
> >>>>> [ 3.116503] ? rt_spin_unlock+0x50/0xa0
> >>>>> [ 3.116503] ? __pfx_kernel_init+0x10/0x10
> >>>>> [ 3.116503] kernel_init+0x23/0x160
> >>>>> [ 3.116503] ? __pfx_kernel_init+0x10/0x10
> >>>>> [ 3.116503] ret_from_fork+0x40/0x60
> >>>>> [ 3.116503] ? __pfx_kernel_init+0x10/0x10
> >>>>> [ 3.116503] ret_from_fork_asm+0x1b/0x30
> >>>>> [ 3.116503] </TASK>
> >>>>> [ 3.116503] non-slab/vmalloc memory
> >>>>>
> >>>>>
> >>>>> as described by Lei Zhen:
> >>>>>
> >>>>> v2 --> v3:
> >>>>> 1. I made statistics about the source of 'rhp'. kmem_valid_obj() accounts for
> >>>>> more than 97.5%, and vmalloc accounts for less than 1%. So change call
> >>>>> mem_dump_obj() to call kmem_dump_obj() can meet debugging requirements and
> >>>>> avoid the potential deadlock risk of vmalloc_dump_obj().
> >>>>> - mem_dump_obj(rhp);
> >>>>> + if (kmem_valid_obj(rhp))
> >>>>> + kmem_dump_obj(rhp);
> >>>>>
> >>>
> >>> I kind of dislike that even if it is just 1%.
> >>>
> >>> Another option is, Could you do the object dump from irq_work if it is
> >>> a vmalloc address? That way there will be no vmap area lock held and
> >>> no need to use workqueue or depend on schedule. And also disable the
> >>> dump for PREEMPT_RT (since that's SWA violation).
> >>
> >>>
> >>
> >> Hello Joel
> >>
> >> Actually I want to know, is it necessary to dump the information of vmalloc
>
> I see. That is worth looking into..
>
> >>
> >>
> >>>
> >>> I feel like this is a PREEMPT_RT problem and we should not make the
> >>> !PREEMPT_RT debugging less effective for their sake.
> >>>
> >>> Maybe soemthing like:
> >>>
> >>> if (kmem_valid_obj(rhp)) {
> >>> kmem_dump_obj(rhp);
> >>> } else if (!in_interrupt() && !IS_ENABLED(CONFIG_PREEMPT_RT) {
> >>> mem_dump_obj(rhp);
> >>> } else if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
> >>> // Queue an irq work to dump, drop CB list on the floor like Paul
> >>> suggested and adjust RCU
> >>> }
> >>
> >> I did something like this earlier:
> >>
> >> https://lore.kernel.org/lkml/20221118003441.3980437-1-qiang1.zhang@xxxxxxxxx/
>
> Cool.
>
> >>
> >>>
> >>> ?
> >>>
> >>> Perhaps the above can be wrapped in a helper and generically used...
> >>>
> >>>> The discussion about vmap_area_lock deadlock in v2:
> >>>> https://lkml.org/lkml/2022/11/11/493
> >>>>
> >>>> so whether mem_dump_obj() should also be replaced by kmem_dump_obj() in
> >>>> __call_rcu_common(), since the call_rcu() can be called in interrupt context,
> >>>> this may issue recursive spin vmap_area_lock lock calls.
> >>>
> >>> That's why it could be done from irq_work.
> >>>
> >>> Thoughts?
> >
> > Even with irq_work to dump vmalloc info also need held vmap_area_lock spinlock,
> > need to make sure that the vm_struct object is not freed
>
> This is true, I realized only after just sending my email. The trick I was referring
> to was avoidance of deadlocks for irq disabled spin locks but this one is not.
>
> So perhaps WQ it is then.. or dropping vmalloc debug..
But only for PREEMPT_RT, correct? Or does the problem also extend to
!PREEMPT_RT?
Thanx, Paul
