Message-ID: <20210810235336.GQ4126399@paulmck-ThinkPad-P17-Gen-1>
Date:   Tue, 10 Aug 2021 16:53:36 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Mike Galbraith <efault@....de>,
        Qian Cai <quic_qiancai@...cinc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v4 29/35] mm: slub: Move flush_cpu_slab() invocations
 __free_slab() invocations out of IRQ context

On Wed, Aug 11, 2021 at 12:36:00AM +0200, Vlastimil Babka wrote:
> On 8/10/2021 10:31 PM, Paul E. McKenney wrote:
> > On Tue, Aug 10, 2021 at 01:47:42PM +0200, Mike Galbraith wrote:
> >> On Tue, 2021-08-10 at 11:03 +0200, Vlastimil Babka wrote:
> >>> On 8/9/21 3:41 PM, Qian Cai wrote:
> >>>>>  
> >>>>> +static DEFINE_MUTEX(flush_lock);
> >>>>> +static DEFINE_PER_CPU(struct slub_flush_work, slub_flush);
> >>>>> +
> >>>>>  static void flush_all(struct kmem_cache *s)
> >>>>>  {
> >>>>> -       on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1);
> >>>>> +       struct slub_flush_work *sfw;
> >>>>> +       unsigned int cpu;
> >>>>> +
> >>>>> +       mutex_lock(&flush_lock);
> >>>>
> >>>> Vlastimil, taking the lock here could trigger a warning during memory offline/online due to the locking order:
> >>>>
> >>>> slab_mutex -> flush_lock
> >>>>
> >>>> [   91.374541] WARNING: possible circular locking dependency detected
> >>>> [   91.381411] 5.14.0-rc5-next-20210809+ #84 Not tainted
> >>>> [   91.387149] ------------------------------------------------------
> >>>> [   91.394016] lsbug/1523 is trying to acquire lock:
> >>>> [   91.399406] ffff800018e76530 (flush_lock){+.+.}-{3:3}, at: flush_all+0x50/0x1c8
> >>>> [   91.407425]
> >>>>                but task is already holding lock:
> >>>> [   91.414638] ffff800018e48468 (slab_mutex){+.+.}-{3:3}, at: slab_memory_callback+0x44/0x280
> >>>> [   91.423603]
> >>>>                which lock already depends on the new lock.
> >>>>
> >>>
> >>> OK, managed to reproduce in qemu and this fixes it for me on top of
> >>> next-20210809. Could you test as well, as your testing might be more
> >>> comprehensive? I will format is as a fixup for the proper patch in the series then.
> >>
> >> As it appeared it should, moving cpu_hotplug_lock outside slab_mutex in
> >> kmem_cache_destroy() on top of that silenced the cpu offline gripe.
> > 
> > And this one got rid of the remainder of the deadlock, but gets me the
> > splat shown at the end of this message.  So some sort of middle ground
> > may be needed.
> > 
> > (Same reproducer as in my previous reply to Vlastimil.)
> > 
> > 							Thanx, Paul
> > 
> >> ---
> >>  mm/slab_common.c |    2 ++
> >>  mm/slub.c        |    2 +-
> >>  2 files changed, 3 insertions(+), 1 deletion(-)
> >>
> >> --- a/mm/slab_common.c
> >> +++ b/mm/slab_common.c
> >> @@ -502,6 +502,7 @@ void kmem_cache_destroy(struct kmem_cach
> >>  	if (unlikely(!s))
> >>  		return;
> >>
> >> +	cpus_read_lock();
> >>  	mutex_lock(&slab_mutex);
> >>
> >>  	s->refcount--;
> >> @@ -516,6 +517,7 @@ void kmem_cache_destroy(struct kmem_cach
> >>  	}
> >>  out_unlock:
> >>  	mutex_unlock(&slab_mutex);
> >> +	cpus_read_unlock();
> >>  }
> >>  EXPORT_SYMBOL(kmem_cache_destroy);
> >>
> >> --- a/mm/slub.c
> >> +++ b/mm/slub.c
> >> @@ -4234,7 +4234,7 @@ int __kmem_cache_shutdown(struct kmem_ca
> >>  	int node;
> >>  	struct kmem_cache_node *n;
> >>
> >> -	flush_all(s);
> >> +	flush_all_cpus_locked(s);
> >>  	/* Attempt to free all objects */
> >>  	for_each_kmem_cache_node(s, node, n) {
> >>  		free_partial(s, n);
> > 
> > [  602.539109] ------------[ cut here ]------------
> > [  602.539804] WARNING: CPU: 3 PID: 88 at kernel/cpu.c:335 lockdep_assert_cpus_held+0x29/0x30
> 
> So this says the assert failed and we don't have the cpus_read_lock(), right, but...
> 
> > [  602.540940] Modules linked in:
> > [  602.541377] CPU: 3 PID: 88 Comm: torture_shutdow Not tainted 5.14.0-rc5-next-20210809+ #3299
> > [  602.542536] Hardware name: Red Hat KVM/RHEL-AV, BIOS 1.13.0-2.module_el8.5.0+746+bbd5d70c 04/01/2014
> > [  602.543786] RIP: 0010:lockdep_assert_cpus_held+0x29/0x30
> > [  602.544524] Code: 00 83 3d 4d f1 a4 01 01 76 0a 8b 05 4d 23 a5 01 85 c0 75 01 c3 be ff ff ff ff 48 c7 c7 b0 86 66 a3 e8 9b 05 c9 00 85 c0 75 ea <0f> 0b c3 0f 1f 40 00 41 57 41 89 ff 41 56 4d 89 c6 41 55 49 89 cd
> > [  602.547051] RSP: 0000:ffffb382802efdb8 EFLAGS: 00010246
> > [  602.547783] RAX: 0000000000000000 RBX: ffffa23301a44000 RCX: 0000000000000001
> > [  602.548764] RDX: 0000000000000001 RSI: ffffffffa335f5c0 RDI: ffffffffa33adbbf[  602.549747] RBP: ffffa23301a44000 R08: ffffa23302810000 R09: 974cf0ba5c48ad3c
> > [  602.550727] R10: ffffb382802efe78 R11: 0000000000000001 R12: ffffa23301a44000[  602.551709] R13: 00000000000249c0 R14: 00000000ffffffff R15: 0000000fffffffe0
> > [  602.552694] FS:  0000000000000000(0000) GS:ffffa2331f580000(0000) knlGS:0000000000000000
> > [  602.553805] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [  602.554606] CR2: 0000000000000000 CR3: 0000000017222000 CR4: 00000000000006e0
> > [  602.555601] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [  602.556590] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > [  602.557585] Call Trace:
> > [  602.557927]  flush_all_cpus_locked+0x29/0x140
> > [  602.558535]  __kmem_cache_shutdown+0x26/0x200
> > [  602.559145]  ? lock_is_held_type+0xd6/0x130
> > [  602.559739]  ? torture_onoff+0x260/0x260
> > [  602.560284]  kmem_cache_destroy+0x38/0x110
> 
> It should have been taken here. I don't understand. It's as if only the
> mm/slub.c was patched by Mike's patch, but mm/slab_common.c not?

You know, you would think that I would have learned how to reliably
apply a patch by now.  Apparently not this morning.

Anyway, right in one!  I will try again with the full patch later.

							Thanx, Paul

> > [  602.560859]  rcu_torture_cleanup.cold.36+0x192/0x421
> > [  602.561539]  ? wait_woken+0x60/0x60
> > [  602.562035]  ? torture_onoff+0x260/0x260
> > [  602.562591]  torture_shutdown+0xdd/0x1c0
> > [  602.563131]  kthread+0x132/0x160
> > [  602.563592]  ? set_kthread_struct+0x40/0x40
> > [  602.564172]  ret_from_fork+0x22/0x30
> > [  602.564696] irq event stamp: 1307
> > [  602.565161] hardirqs last  enabled at (1315): [<ffffffffa1eddced>] __up_console_sem+0x4d/0x50
> > [  602.566321] hardirqs last disabled at (1324): [<ffffffffa1eddcd2>] __up_console_sem+0x32/0x50
> > [  602.567479] softirqs last  enabled at (1304): [<ffffffffa2e00311>] __do_softirq+0x311/0x473
> > [  602.568616] softirqs last disabled at (1299): [<ffffffffa1e72eb8>] irq_exit_rcu+0xe8/0xf0
> > [  602.569735] ---[ end trace 26fd643e1df331c9 ]---
> > 
> 

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