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Message-ID: <1569500974.5576.234.camel@lca.pw>
Date: Thu, 26 Sep 2019 08:29:34 -0400
From: Qian Cai <cai@....pw>
To: Peter Zijlstra <peterz@...radead.org>
Cc: akpm@...ux-foundation.org, bigeasy@...utronix.de,
tglx@...utronix.de, thgarnie@...gle.com, tytso@....edu,
cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
mingo@...hat.com, will@...nel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, keescook@...omium.org
Subject: Re: [PATCH] mm/slub: fix a deadlock in shuffle_freelist()
On Wed, 2019-09-25 at 18:45 +0200, Peter Zijlstra wrote:
> On Wed, Sep 25, 2019 at 11:18:47AM -0400, Qian Cai wrote:
> > On Wed, 2019-09-25 at 11:31 +0200, Peter Zijlstra wrote:
> > > On Fri, Sep 13, 2019 at 12:27:44PM -0400, Qian Cai wrote:
> > > > -> #3 (batched_entropy_u32.lock){-.-.}:
> > > > lock_acquire+0x31c/0x360
> > > > _raw_spin_lock_irqsave+0x7c/0x9c
> > > > get_random_u32+0x6c/0x1dc
> > > > new_slab+0x234/0x6c0
> > > > ___slab_alloc+0x3c8/0x650
> > > > kmem_cache_alloc+0x4b0/0x590
> > > > __debug_object_init+0x778/0x8b4
> > > > debug_object_init+0x40/0x50
> > > > debug_init+0x30/0x29c
> > > > hrtimer_init+0x30/0x50
> > > > init_dl_task_timer+0x24/0x44
> > > > __sched_fork+0xc0/0x168
> > > > init_idle+0x78/0x26c
> > > > fork_idle+0x12c/0x178
> > > > idle_threads_init+0x108/0x178
> > > > smp_init+0x20/0x1bc
> > > > kernel_init_freeable+0x198/0x26c
> > > > kernel_init+0x18/0x334
> > > > ret_from_fork+0x10/0x18
> > > >
> > > > -> #2 (&rq->lock){-.-.}:
> > >
> > > This relation is silly..
> > >
> > > I suspect the below 'works'...
> >
> > Unfortunately, the relation is still there,
> >
> > copy_process()->rt_mutex_init_task()->"&p->pi_lock"
> >
> > [24438.676716][ T2] -> #2 (&rq->lock){-.-.}:
> > [24438.676727][ T2] __lock_acquire+0x5b4/0xbf0
> > [24438.676736][ T2] lock_acquire+0x130/0x360
> > [24438.676754][ T2] _raw_spin_lock+0x54/0x80
> > [24438.676771][ T2] task_fork_fair+0x60/0x190
> > [24438.676788][ T2] sched_fork+0x128/0x270
> > [24438.676806][ T2] copy_process+0x7a4/0x1bf0
> > [24438.676823][ T2] _do_fork+0xac/0xac0
> > [24438.676841][ T2] kernel_thread+0x70/0xa0
> > [24438.676858][ T2] rest_init+0x4c/0x42c
> > [24438.676884][ T2] start_kernel+0x778/0x7c0
> > [24438.676902][ T2] start_here_common+0x1c/0x334
>
> That's the 'where we took #2 while holding #1' stacktrace and not
> relevant to our discussion.
Oh, you were talking about took #3 while holding #2. Anyway, your patch is
working fine so far. Care to post/merge it officially or do you want me to post
it?
>
> > [24438.675836][ T2] -> #4 (batched_entropy_u64.lock){-...}:
> > [24438.675860][ T2] __lock_acquire+0x5b4/0xbf0
> > [24438.675878][ T2] lock_acquire+0x130/0x360
> > [24438.675906][ T2] _raw_spin_lock_irqsave+0x70/0xa0
> > [24438.675923][ T2] get_random_u64+0x60/0x100
> > [24438.675944][ T2] add_to_free_area_random+0x164/0x1b0
> > [24438.675962][ T2] free_one_page+0xb24/0xcf0
> > [24438.675980][ T2] __free_pages_ok+0x448/0xbf0
> > [24438.675999][ T2] deferred_init_maxorder+0x404/0x4a4
> > [24438.676018][ T2] deferred_grow_zone+0x158/0x1f0
> > [24438.676035][ T2] get_page_from_freelist+0x1dc8/0x1e10
> > [24438.676063][ T2] __alloc_pages_nodemask+0x1d8/0x1940
> > [24438.676083][ T2] allocate_slab+0x130/0x2740
> > [24438.676091][ T2] new_slab+0xa8/0xe0
> > [24438.676101][ T2] kmem_cache_open+0x254/0x660
> > [24438.676119][ T2] __kmem_cache_create+0x44/0x2a0
> > [24438.676136][ T2] create_boot_cache+0xcc/0x110
> > [24438.676154][ T2] kmem_cache_init+0x90/0x1f0
> > [24438.676173][ T2] start_kernel+0x3b8/0x7c0
> > [24438.676191][ T2] start_here_common+0x1c/0x334
> > [24438.676208][ T2]
> > [24438.676208][ T2] -> #3 (&(&zone->lock)->rlock){-.-.}:
> > [24438.676221][ T2] __lock_acquire+0x5b4/0xbf0
> > [24438.676247][ T2] lock_acquire+0x130/0x360
> > [24438.676264][ T2] _raw_spin_lock+0x54/0x80
> > [24438.676282][ T2] rmqueue_bulk.constprop.23+0x64/0xf20
> > [24438.676300][ T2] get_page_from_freelist+0x718/0x1e10
> > [24438.676319][ T2] __alloc_pages_nodemask+0x1d8/0x1940
> > [24438.676339][ T2] alloc_page_interleave+0x34/0x170
> > [24438.676356][ T2] allocate_slab+0xd1c/0x2740
> > [24438.676374][ T2] new_slab+0xa8/0xe0
> > [24438.676391][ T2] ___slab_alloc+0x580/0xef0
> > [24438.676408][ T2] __slab_alloc+0x64/0xd0
> > [24438.676426][ T2] kmem_cache_alloc+0x5c4/0x6c0
> > [24438.676444][ T2] fill_pool+0x280/0x540
> > [24438.676461][ T2] __debug_object_init+0x60/0x6b0
> > [24438.676479][ T2] hrtimer_init+0x5c/0x310
> > [24438.676497][ T2] init_dl_task_timer+0x34/0x60
> > [24438.676516][ T2] __sched_fork+0x8c/0x110
> > [24438.676535][ T2] init_idle+0xb4/0x3c0
> > [24438.676553][ T2] idle_thread_get+0x78/0x120
> > [24438.676572][ T2] bringup_cpu+0x30/0x230
> > [24438.676590][ T2] cpuhp_invoke_callback+0x190/0x1580
> > [24438.676618][ T2] do_cpu_up+0x248/0x460
> > [24438.676636][ T2] smp_init+0x118/0x1c0
> > [24438.676662][ T2] kernel_init_freeable+0x3f8/0x8dc
> > [24438.676681][ T2] kernel_init+0x2c/0x154
> > [24438.676699][ T2] ret_from_kernel_thread+0x5c/0x74
> > [24438.676716][ T2]
> > [24438.676716][ T2] -> #2 (&rq->lock){-.-.}:
>
> This then shows we now have:
>
> rq->lock
> zone->lock.rlock
> batched_entropy_u64.lock
>
> Which, to me, appears to be distinctly different from the last time,
> which was:
>
> rq->lock
> batched_entropy_u32.lock
>
> Notable: "u32" != "u64".
>
> But #3 has:
>
> > [24438.676516][ T2] __sched_fork+0x8c/0x110
> > [24438.676535][ T2] init_idle+0xb4/0x3c0
>
> Which seems to suggest you didn't actually apply the patch; or rather,
> if you did, i'm not immediately seeing where #2 is acquired.
>
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