Re: 2.6.14-rc1-git-now still dying in mm/slab - this time line 1849

[Petr Vandrovec <vandrove@vc.cvut.cz>]

Andrew Morton wrote:
> Petr Vandrovec <vandrove@vc.cvut.cz> wrote:
>
> > Andrew Morton wrote:
> >
> > > Petr Vandrovec <vandrove@vc.cvut.cz> wrote:
> > >
> > >
> > > > Andrew Morton wrote:
> > > >
> > > > > Petr Vandrovec <vandrove@vc.cvut.cz> wrote:
> > > > >
> > > > >
> > > > > >  so now once crashes on UP system were sorted out, I tried to
> > > > > > put new kernel on my SMP host - and sorry to say, but it does not
> > > > > > seem to work as advertised :-(
> > > > >
> > > > > .config (again), please.
> > > >
> > > > Any SMP with NUMA.  One which I'm trying to debug now is attached.
> > > > It is available at http://vana.vc.cvut.cz/config as well.
> > >
> > > I can get 2.6.14-rc1 to crash with your .config, but current -linus is OK.
> >
> > It still dies for me, with current git (tree 7513cdadc661cfe0bd1625145a4876e54df191ca,
> > commit 6c0741fbdee5bd0f8ed13ac287c4ab18e8ba7d83).  Config is available at
> > http://platan.vc.cvut.cz/config-vana.txt.  Box is dual opteron Tyan K8W, S2885.
> >
> > ...
> >
> >     ide0: BM-DMA at 0xffa0-0xffa7, BIOS settings: hda:DMA, hdb:pio
> >     ide1: BM-DMA at 0xffa8-0xffaf, BIOS settings: hdc:DMA, hdd:pio
> > ----------- [cut here ] --------- [please bite here ] ---------
> > Kernel BUG at mm/slab.c:1849
> > invalid operand: 0000 [1] SMP
> > CPU 0
> > Modules linked in:
> > Pid: 8, comm: events/0 Not tainted 2.6.14-rc1-6c07 #1
> > RIP: 0010:[<ffffffff8016d316>] <ffffffff8016d316>{free_block+294}
> > RSP: 0000:ffff81007ff21d88  EFLAGS: 00010002
> > RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000310
> > RDX: 0000000000000000 RSI: ffff81007ffddd10 RDI: ffff81007ffda080
> > RBP: ffff81007ffde000 R08: ffff81003ffa0d50 R09: 0000000000000000
> > R10: 00000000ffffffff R11: 0000000000000000 R12: ffff81007ffc9b50
> > R13: ffff81007ffde048 R14: ffff81007ffda080 R15: ffff81007ffda080
> > FS:  0000000000000000(0000) GS:ffffffff805f2800(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
> > CR2: 0000000000000000 CR3: 0000000000101000 CR4: 00000000000006e0
> > Process events/0 (pid: 8, threadinfo ffff81007ff20000, task ffff81003ff8c790)
> > Stack: 0000000000000000 0000000000000000 0000000000000292 hda: _NEC DVD_RW ND-3500AG, ATAPI CD/DVD-ROM drive
> > 0000000200000000
> >        ffff81007ffddd10 ffff81007ffddd10 ffff81007ffddce8 0000000000000002
> >        0000000000000000 ffff81007ffda080
> > Call Trace:<ffffffff8016e8b7>{drain_array_locked+167} <ffffffff8016e9f7>{cache_reap+231}
> >        <ffffffff80131e23>{__wake_up+67} <ffffffff8016e910>{cache_reap+0}
> >        <ffffffff8014930c>{worker_thread+476} <ffffffff80131d60>{default_wake_function+0}
> >        <ffffffff80131d60>{default_wake_function+0} <ffffffff80149130>{worker_thread+0}
> >        <ffffffff8014db82>{kthread+146} <ffffffff8010ec22>{child_rip+8}
> >        <ffffffff80149130>{worker_thread+0} <ffffffff8014daf0>{kthread+0}
> >        <ffffffff8010ec1a>{child_rip+0}
> >
> > Code: 0f 0b 68 9d 26 3d 80 c2 39 07 48 89 ee 4c 89 ff 4c 8d 75 30
> > RIP <ffffffff8016d316>{free_block+294} RSP <ffff81007ff21d88>
> >  ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
>
>
> Well.  The CPU_UP_CANCELED locking in cpuup_callback() looks borked to me -
> it takes cachep->nodelists[node]->list_lock and then calls
> drain_alien_cache() which appears to take the same lock.  But that's not
> the problem here.
>
> The code in cache_reap() recalculates numa_node_id() multiple times, so if
> the caller changes CPUs then this assertion will trigger.  However it's
> running under keventd here, which is pinned to a single CPU.  Still, it
> would be useful if you could try putting preempt_disable()s in
> cache_reap(), or change cache_reap() to evaluate numa_node_id() just the
> once, and cache that in a local variable.
>
> I wonder why numa_node_id() uses raw_smp_processor_id()?  That's just
> asking for preempt non-atomicity bugs.

I've thought that this is problem, but as far as I can tell while this is
problem it does not happen here.  Just free_block() finds that pointer it
got from caller belongs to the slab that belongs to the CPU#1/node#1
while caller obtained lock on CPU#0/node#0 structures.  Which suggests
that drain_array_locked() was issued with node #0 while array_cache->entry
it got contains blocks which belong to node #1.  Which I cannot explain.
								Petr

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