>
>
> On 2023/4/11 22:19, Vlastimil Babka wrote:
> > On 4/11/23 16:08, Qi Zheng wrote:
> > >
> > >
> > > On 2023/4/11 21:40, Vlastimil Babka wrote:
> > > > On 4/11/23 15:08, Qi Zheng wrote:
> > > > > The list_lock can be held in the critical section of
> > > > > raw_spinlock, and then lockdep will complain about it
> > > > > like below:
> > > > >
> > > > > =============================
> > > > > [ BUG: Invalid wait context ]
> > > > > 6.3.0-rc6-next-20230411 #7 Not tainted
> > > > > -----------------------------
> > > > > swapper/0/1 is trying to lock:
> > > > > ffff888100055418 (&n->list_lock){....}-{3:3}, at: ___slab_alloc+0x73d/0x1330
> > > > > other info that might help us debug this:
> > > > > context-{5:5}
> > > > > 2 locks held by swapper/0/1:
> > > > > #0: ffffffff824e8160 (rcu_tasks.cbs_gbl_lock){....}-{2:2}, at: cblist_init_generic+0x22/0x2d0
> > > > > #1: ffff888136bede50 (&ACCESS_PRIVATE(rtpcp, lock)){....}-{2:2}, at: cblist_init_generic+0x232/0x2d0
> > > > > stack backtrace:
> > > > > CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.3.0-rc6-next-20230411 #7
> > > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
> > > > > Call Trace:
> > > > > <TASK>
> > > > > dump_stack_lvl+0x77/0xc0
> > > > > __lock_acquire+0xa65/0x2950
> > > > > ? arch_stack_walk+0x65/0xf0
> > > > > ? arch_stack_walk+0x65/0xf0
> > > > > ? unwind_next_frame+0x602/0x8d0
> > > > > lock_acquire+0xe0/0x300
> > > > > ? ___slab_alloc+0x73d/0x1330
> > > > > ? find_usage_forwards+0x39/0x50
> > > > > ? check_irq_usage+0x162/0xa70
> > > > > ? __bfs+0x10c/0x2c0
> > > > > _raw_spin_lock_irqsave+0x4f/0x90
> > > > > ? ___slab_alloc+0x73d/0x1330
> > > > > ___slab_alloc+0x73d/0x1330
> > > > > ? fill_pool+0x16b/0x2a0
> > > > > ? look_up_lock_class+0x5d/0x160
> > > > > ? register_lock_class+0x48/0x500
> > > > > ? __lock_acquire+0xabc/0x2950
> > > > > ? fill_pool+0x16b/0x2a0
> > > > > kmem_cache_alloc+0x358/0x3b0
> > > > > ? __lock_acquire+0xabc/0x2950
> > > > > fill_pool+0x16b/0x2a0
> > > > > ? __debug_object_init+0x292/0x560
> > > > > ? lock_acquire+0xe0/0x300
> > > > > ? cblist_init_generic+0x232/0x2d0
> > > > > __debug_object_init+0x2c/0x560
>
>This "__debug_object_init" is because INIT_WORK() is called in
>cblist_init_generic(), so..
>
> > > > > cblist_init_generic+0x147/0x2d0
> > > > > rcu_init_tasks_generic+0x15/0x190
> > > > > kernel_init_freeable+0x6e/0x3e0
> > > > > ? rest_init+0x1e0/0x1e0
> > > > > kernel_init+0x1b/0x1d0
> > > > > ? rest_init+0x1e0/0x1e0
> > > > > ret_from_fork+0x1f/0x30
> > > > > </TASK>
> > > > >
> > > > > The fill_pool() can only be called in the !PREEMPT_RT kernel
> > > > > or in the preemptible context of the PREEMPT_RT kernel, so
> > > > > the above warning is not a real issue, but it's better to
> > > > > annotate kmem_cache_node->list_lock as raw_spinlock to get
> > > > > rid of such issue.
> > > >
> > > > + CC some RT and RCU people
> > >
> > > Thanks.
> > >
> > > >
> > > > AFAIK raw_spinlock is not just an annotation, but on RT it changes the
> > > > implementation from preemptible mutex to actual spin lock, so it would be
> > >
> > > Yeah.
> > >
> > > > rather unfortunate to do that for a spurious warning. Can it be somehow
> > > > fixed in a better way?
>
>... probably a better fix is to drop locks and call INIT_WORK(), or make
>the cblist_init_generic() lockless (or part lockless), given it's just
>initializing the cblist, it's probably doable. But I haven't taken a
>careful look yet.
>
This is just one of the paths that triggers an invalid wait, the following paths can also trigger:
[ 129.914547] [ BUG: Invalid wait context ]
[ 129.914775] 6.3.0-rc1-yocto-standard+ #2 Not tainted
[ 129.915044] -----------------------------
[ 129.915272] kworker/2:0/28 is trying to lock:
[ 129.915516] ffff88815660f570 (&c->lock){-.-.}-{3:3}, at: ___slab_alloc+0x68/0x12e0
[ 129.915967] other info that might help us debug this:
[ 129.916241] context-{5:5}
[ 129.916392] 3 locks held by kworker/2:0/28:
[ 129.916642] #0: ffff888100084d48 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x515/0xba0
[ 129.917145] #1: ffff888100c17dd0 ((work_completion)(&(&krcp->monitor_work)->work)){+.+.}-{0:0}, at: process_on0
[ 129.917758] #2: ffff8881565f8508 (krc.lock){....}-{2:2}, at: kfree_rcu_monitor+0x29f/0x810
[ 129.918207] stack backtrace:
[ 129.918374] CPU: 2 PID: 28 Comm: kworker/2:0 Not tainted 6.3.0-rc1-yocto-standard+ #2
[ 129.918784] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.1-0-g3208b098f51a-prebuilt.qemu.o4
[ 129.919397] Workqueue: events kfree_rcu_monitor
[ 129.919662] Call Trace:
[ 129.919812] <TASK>
[ 129.919941] dump_stack_lvl+0x64/0xb0
[ 129.920171] dump_stack+0x10/0x20
[ 129.920372] __lock_acquire+0xeb8/0x3a80
[ 129.920603] ? ret_from_fork+0x2c/0x50
[ 129.920824] ? __pfx___lock_acquire+0x10/0x10
[ 129.921068] ? unwind_next_frame.part.0+0x1ba/0x3c0
[ 129.921343] ? ret_from_fork+0x2c/0x50
[ 129.921573] ? __this_cpu_preempt_check+0x13/0x20
[ 129.921847] lock_acquire+0x194/0x480
[ 129.922060] ? ___slab_alloc+0x68/0x12e0
[ 129.922293] ? __pfx_lock_acquire+0x10/0x10
[ 129.922529] ? __pfx_mark_lock.part.0+0x10/0x10
[ 129.922778] ? __kasan_check_read+0x11/0x20
[ 129.922998] ___slab_alloc+0x9a/0x12e0
[ 129.923222] ? ___slab_alloc+0x68/0x12e0
[ 129.923452] ? __pfx_mark_lock.part.0+0x10/0x10
[ 129.923706] ? __kasan_check_read+0x11/0x20
[ 129.923937] ? fill_pool+0x22a/0x370
[ 129.924161] ? __lock_acquire+0xf5b/0x3a80
[ 129.924387] ? fill_pool+0x22a/0x370
[ 129.924590] __slab_alloc.constprop.0+0x5b/0x90
[ 129.924832] kmem_cache_alloc+0x296/0x3d0
[ 129.925073] ? fill_pool+0x22a/0x370
[ 129.925291] fill_pool+0x22a/0x370
[ 129.925495] ? __pfx_fill_pool+0x10/0x10
[ 129.925718] ? __pfx___lock_acquire+0x10/0x10
[ 129.926034] ? __kasan_check_read+0x11/0x20
[ 129.926269] ? check_chain_key+0x200/0x2b0
[ 129.926503] __debug_object_init+0x82/0x8c0
[ 129.926734] ? __pfx_lock_release+0x10/0x10
[ 129.926984] ? __pfx___debug_object_init+0x10/0x10
[ 129.927249] ? __kasan_check_read+0x11/0x20
[ 129.927498] ? do_raw_spin_unlock+0x9c/0x100
[ 129.927758] debug_object_activate+0x2d1/0x2f0
[ 129.928022] ? __pfx_debug_object_activate+0x10/0x10
[ 129.928300] ? __this_cpu_preempt_check+0x13/0x20
[ 129.928583] __call_rcu_common.constprop.0+0x94/0xeb0
[ 129.928897] ? __this_cpu_preempt_check+0x13/0x20
[ 129.929186] ? __pfx_rcu_work_rcufn+0x10/0x10
[ 129.929459] ? __pfx___call_rcu_common.constprop.0+0x10/0x10
[ 129.929803] ? __pfx_lock_acquired+0x10/0x10
[ 129.930067] ? __pfx_do_raw_spin_trylock+0x10/0x10
[ 129.930363] ? kfree_rcu_monitor+0x29f/0x810
[ 129.930627] call_rcu+0xe/0x20
[ 129.930821] queue_rcu_work+0x4f/0x60
[ 129.931050] kfree_rcu_monitor+0x5d3/0x810
[ 129.931302] ? __pfx_kfree_rcu_monitor+0x10/0x10
[ 129.931587] ? __this_cpu_preempt_check+0x13/0x20
[ 129.931878] process_one_work+0x607/0xba0
[ 129.932129] ? __pfx_process_one_work+0x10/0x10
[ 129.932408] ? worker_thread+0xd6/0x710
[ 129.932653] worker_thread+0x2d4/0x710
[ 129.932888] ? __pfx_worker_thread+0x10/0x10
[ 129.933154] kthread+0x18b/0x1c0
[ 129.933363] ? __pfx_kthread+0x10/0x10
[ 129.933598] ret_from_fork+0x2c/0x50
[ 129.933825] </TASK>
Maybe no need to convert ->list_lock to raw_spinlock.
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -562,10 +562,10 @@ __debug_object_init(void *addr, const struct debug_obj_descr *descr, int onstack
unsigned long flags;
/*
- * On RT enabled kernels the pool refill must happen in preemptible
+ * The pool refill must happen in preemptible
* context:
*/
- if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible())
+ if (preemptible())
fill_pool();
db = get_bucket((unsigned long) addr);
Thanks
Zqiang
>
>
>Regards,
>Boqun
>
> > >
> > > It's indeed unfortunate for the warning in the commit message. But
> > > functions like kmem_cache_alloc(GFP_ATOMIC) may indeed be called
> > > in the critical section of raw_spinlock or in the hardirq context, which
> >
> > Hmm, I thought they may not, actually.
> >
> > > will cause problem in the PREEMPT_RT kernel. So I still think it is
> > > reasonable to convert kmem_cache_node->list_lock to raw_spinlock type.
> >
> > It wouldn't be the complete solution anyway. Once we allow even a GFP_ATOMIC
> > slab allocation for such context, it means also page allocation can happen
> > to refill the slabs, so lockdep will eventually complain about zone->lock,
> > and who knows what else.
>
> Oh, indeed. :(
>
> >
> > > In addition, there are many fix patches for this kind of warning in the
> > > git log, so I also think there should be a general and better solution. :)
> >
> > Maybe, but given above, I doubt it's this one.
> >
> > >
> > > >
> > >
> >
>
> --
> Thanks,
> Qi
