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Date:	Thu, 10 Jul 2014 10:55:33 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Sasha Levin <sasha.levin@...cle.com>
cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Hugh Dickins <hughd@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>, akpm@...ux-foundation.org,
	davej@...hat.com, koct9i@...il.com, lczerner@...hat.com,
	stable@...r.kernel.org, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: + shmem-fix-faulting-into-a-hole-while-its-punched-take-2.patch
 added to -mm tree

On Thu, 10 Jul 2014, Sasha Levin wrote:
> On 07/10/2014 08:46 AM, Sasha Levin wrote:
> > On 07/10/2014 03:37 AM, Hugh Dickins wrote:
> >> > I do think that the most useful thing you could do at the moment,
> >> > is to switch away from running trinity on -next temporarily, and
> >> > run it instead on Linus's current git or on 3.16-rc4, but with
> >> > f00cdc6df7d7 reverted and my "take 2" inserted in its place.
> >> > 
> >> > That tree would also include Heiko's seq_buf_alloc() patch, which
> >> > trinity on -next has cast similar doubt upon: at present, we do
> >> > not know if Heiko's patch and my patch are bad in themselves,
> >> > or exposing other bugs in 3.16-rc, or exposing bugs in -next.
> > Funny enough, Linus's tree doesn't even boot properly here. It's
> > going to take longer than I expected...

Thanks a lot for getting down to this so quickly.

> 
> While I'm failing to reproduce the mountinfo issue on Linus's tree,

That's good news for Heiko's patch:
no reason to rush and revert it, I guess.

> the shmem_fallocate one reproduces rather easily.

"Good" news of the opposite kind ;)  Very useful to know that.

> 
> I've reverted your original fix and applied the "take 2" one as you
> suggested, there are no other significant changes on top on Linus's
> tree in this case (just Heiko's test patch and some improvements to
> what gets printed on hung tasks plus an assortment on unrelated fixes
> that are present in next).

Just right, thanks.

> 
> The same structure of locks that was analysed in -next exists here
> as well:
> 
> Triggered here:
> 
> [  364.601210] INFO: task trinity-c214:9083 blocked for more than 120 seconds.
> [  364.605498]       Not tainted 3.16.0-rc4-sasha-00069-g615ded7-dirty #793
> [  364.609705] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [  364.614939] trinity-c214    D 0000000000000002 13528  9083   8490 0x00000000
> [  364.619414]  ffff880018757ce8 0000000000000002 ffffffff91a01d70 0000000000000001
> [  364.624540]  ffff880018757fd8 00000000001d7740 00000000001d7740 00000000001d7740
> [  364.629378]  ffff880006428000 ffff880018758000 ffff880018757cd8 ffff880031fdc210
> [  364.650601] Call Trace:
> [  364.652252] schedule (kernel/sched/core.c:2832)
> [  364.655337] schedule_preempt_disabled (kernel/sched/core.c:2859)
> [  364.659287] mutex_lock_nested (kernel/locking/mutex.c:535 kernel/locking/mutex.c:587)
> [  364.663131] ? shmem_fallocate (mm/shmem.c:1738)
> [  364.666616] ? get_parent_ip (kernel/sched/core.c:2546)
> [  364.670454] ? shmem_fallocate (mm/shmem.c:1738)
> [  364.674159] shmem_fallocate (mm/shmem.c:1738)
> [  364.676589] ? SyS_madvise (mm/madvise.c:334 mm/madvise.c:384 mm/madvise.c:534 mm/madvise.c:465)
> [  364.678415] ? put_lock_stats.isra.12 (./arch/x86/include/asm/preempt.h:98 kernel/locking/lockdep.c:254)
> [  364.680806] ? SyS_madvise (mm/madvise.c:334 mm/madvise.c:384 mm/madvise.c:534 mm/madvise.c:465)
> [  364.684206] do_fallocate (include/linux/fs.h:1281 fs/open.c:299)
> [  364.687313] SyS_madvise (mm/madvise.c:335 mm/madvise.c:384 mm/madvise.c:534 mm/madvise.c:465)
> [  364.690343] ? context_tracking_user_exit (./arch/x86/include/asm/paravirt.h:809 (discriminator 2) kernel/context_tracking.c:184 (discriminator 2))
> [  364.692913] ? trace_hardirqs_on (kernel/locking/lockdep.c:2607)
> [  364.694450] tracesys (arch/x86/kernel/entry_64.S:543)
> [  364.696034] 2 locks held by trinity-c214/9083:
> [  364.697222] #0: (sb_writers#9){.+.+.+}, at: do_fallocate (fs/open.c:298)
> [  364.700686] #1: (&sb->s_type->i_mutex_key#16){+.+.+.}, at: shmem_fallocate (mm/shmem.c:1738)
> 
> Holding i_mutex and blocking on i_mmap_mutex:
> 
> [  367.615992] trinity-c100    R  running task    13048  8967   8490 0x00000006
> [  367.616039]  ffff88001b903978 0000000000000002 0000000000000006 ffff880404666fd8
> [  367.616075]  ffff88001b903fd8 00000000001d7740 00000000001d7740 00000000001d7740
> [  367.616113]  ffff880007a40000 ffff88001b8f8000 ffff88001b903968 ffff88001b903fd8
> [  367.616152] Call Trace:
> [  367.616165] preempt_schedule_irq (./arch/x86/include/asm/paravirt.h:814 kernel/sched/core.c:2912)
> [  367.616182] retint_kernel (arch/x86/kernel/entry_64.S:937)
> [  367.616198] ? unmap_single_vma (mm/memory.c:1230 mm/memory.c:1277 mm/memory.c:1302 mm/memory.c:1348)
> [  367.616213] ? unmap_single_vma (mm/memory.c:1297 mm/memory.c:1348)
> [  367.616226] zap_page_range_single (include/linux/mmu_notifier.h:234 mm/memory.c:1429)
> [  367.616240] ? get_parent_ip (kernel/sched/core.c:2546)
> [  367.616260] ? unmap_mapping_range (mm/memory.c:2391)
> [  367.616267] unmap_mapping_range (mm/memory.c:2316 mm/memory.c:2392)
> [  367.616271] truncate_inode_page (mm/truncate.c:136 mm/truncate.c:180)
> [  367.616281] shmem_undo_range (mm/shmem.c:429)
> [  367.616289] shmem_truncate_range (mm/shmem.c:528)
> [  367.616296] shmem_fallocate (mm/shmem.c:1749)
> [  367.616301] ? SyS_madvise (mm/madvise.c:334 mm/madvise.c:384 mm/madvise.c:534 mm/madvise.c:465)
> [  367.616307] ? put_lock_stats.isra.12 (./arch/x86/include/asm/preempt.h:98 kernel/locking/lockdep.c:254)
> [  367.616314] ? SyS_madvise (mm/madvise.c:334 mm/madvise.c:384 mm/madvise.c:534 mm/madvise.c:465)
> [  367.616320] do_fallocate (include/linux/fs.h:1281 fs/open.c:299)
> [  367.616326] SyS_madvise (mm/madvise.c:335 mm/madvise.c:384 mm/madvise.c:534 mm/madvise.c:465)
> [  367.616333] ? context_tracking_user_exit (./arch/x86/include/asm/paravirt.h:809 (discriminator 2) kernel/context_tracking.c:184 (discriminator 2))
> [  367.616340] ? trace_hardirqs_on (kernel/locking/lockdep.c:2607)
> [  367.616345] tracesys (arch/x86/kernel/entry_64.S:543)
> 
> And finally, (not) holding the i_mmap_mutex:

I don't understand what prompts you to show this particular task.
I imagine the dump shows lots of other tasks which are waiting to get an
i_mmap_mutex, and quite a lot of other tasks which are neither waiting
for nor holding an i_mmap_mutex.

Why are you showing this one in particular?  Because it looks like the
one you fingered yesterday?  But I didn't see a good reason to finger
that one either.

Mind you, I'm still baffled by the oops on testing PageAnon that you
got a few days ago in zap_pte_range(), so maybe zap_pte_range() does
deserve special attention.

> 
> [  367.638911] trinity-c190    R  running task    12680  9059   8490 0x00000004
> [  367.638928]  ffff8800193db828 0000000000000002 0000000000000030 0000000000000000
> [  367.638937]  ffff8800193dbfd8 00000000001d7740 00000000001d7740 00000000001d7740
> [  367.638943]  ffff8800048eb000 ffff8800193d0000 ffff8800193db818 ffff8800193dbfd8
> [  367.638950] Call Trace:
> [  367.638952]  [<ffffffff8e5170f4>] preempt_schedule_irq+0x84/0x100
> [  367.638956]  [<ffffffff8e51ec50>] retint_kernel+0x20/0x30
> [  367.638960]  [<ffffffff8b290c36>] ? free_hot_cold_page+0x1c6/0x1f0
> [  367.638962]  [<ffffffff8b291566>] free_hot_cold_page_list+0x126/0x1a0
> [  367.638974]  [<ffffffff8b29702e>] release_pages+0x21e/0x250
> [  367.638989]  [<ffffffff8b2cf0c5>] free_pages_and_swap_cache+0x55/0xc0
> [  367.638999]  [<ffffffff8b2b68ac>] tlb_flush_mmu_free+0x4c/0x60
> [  367.639012]  [<ffffffff8b2b8dd1>] zap_pte_range+0x491/0x4f0
> [  367.639019]  [<ffffffff8b2b92ce>] unmap_single_vma+0x49e/0x4c0
> [  367.639025]  [<ffffffff8b2b9675>] unmap_vmas+0x65/0x90
> [  367.639029]  [<ffffffff8b2c3344>] exit_mmap+0xd4/0x180
> [  367.639032]  [<ffffffff8b15c4ab>] mmput+0x5b/0xf0
> [  367.639038]  [<ffffffff8b163043>] do_exit+0x3a3/0xc80
> [  367.639041]  [<ffffffff8bb46d37>] ? debug_smp_processor_id+0x17/0x20
> [  367.639044]  [<ffffffff8b1c2fae>] ? put_lock_stats.isra.12+0xe/0x30
> [  367.639047]  [<ffffffff8e51d100>] ? _raw_spin_unlock_irq+0x30/0x70
> [  367.639051]  [<ffffffff8b1639f4>] do_group_exit+0x84/0xd0
> [  367.639055]  [<ffffffff8b177657>] get_signal_to_deliver+0x807/0x910
> [  367.639059]  [<ffffffff8b1a6eb8>] ? vtime_account_user+0x98/0xb0
> [  367.639063]  [<ffffffff8b0706c7>] do_signal+0x57/0x9a0
> [  367.639066]  [<ffffffff8b1a6eb8>] ? vtime_account_user+0x98/0xb0
> [  367.639070]  [<ffffffff8b19f228>] ? preempt_count_sub+0xd8/0x130
> [  367.639072]  [<ffffffff8b2848d5>] ? context_tracking_user_exit+0x1b5/0x260
> [  367.639078]  [<ffffffff8bb46d13>] ? __this_cpu_preempt_check+0x13/0x20
> [  367.639081]  [<ffffffff8b1c5df4>] ? trace_hardirqs_on_caller+0x1f4/0x290
> [  367.639087]  [<ffffffff8b07104a>] do_notify_resume+0x3a/0xb0
> [  367.639089]  [<ffffffff8e51e02a>] int_signal+0x12/0x17

I'm not sure whether I should ask you to attach the full dump or not:
I learnt very little from yesterday's 11MB, and from what you say this
one will look very similar.  Oh, I'd better ask for it, but I bet you
process these things much faster than I can manage.

Thanks,
Hugh
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