Date:	Mon, 26 May 2014 13:05:18 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Sasha Levin <sasha.levin@...cle.com>
cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Christoph Lameter <cl@...two.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: mm: NULL ptr deref in remove_migration_pte

On Fri, 23 May 2014, Sasha Levin wrote:

> Ping?
> 
> On 05/05/2014 11:51 AM, Sasha Levin wrote:
> > Did anyone have a chance to look at it? I still see it in -next.
> > 
> > 
> > Thanks,
> > Sasha
> > 
> > On 04/16/2014 10:59 AM, Sasha Levin wrote:
> >> Hi all,
> >>
> >> While fuzzing with trinity inside a KVM tools guest running latest -next
> >> kernel I've stumbled on the following:
> >>
> >> [ 2552.313602] BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
> >> [ 2552.315878] IP: __lock_acquire (kernel/locking/lockdep.c:3070 (discriminator 1))
> >> [ 2552.315878] PGD 465836067 PUD 465837067 PMD 0
> >> [ 2552.315878] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> >> [ 2552.315878] Dumping ftrace buffer:
> >> [ 2552.315878]    (ftrace buffer empty)
> >> [ 2552.315878] Modules linked in:
> >> [ 2552.315878] CPU: 6 PID: 16173 Comm: trinity-c364 Tainted: G        W     3.15.0-rc1-next-20140415-sasha-00020-gaa90d09 #398
> >> [ 2552.315878] task: ffff88046548b000 ti: ffff88044e532000 task.ti: ffff88044e532000
> >> [ 2552.320286] RIP: __lock_acquire (kernel/locking/lockdep.c:3070 (discriminator 1))
> >> [ 2552.320286] RSP: 0018:ffff88044e5339c8  EFLAGS: 00010002
> >> [ 2552.320286] RAX: 0000000000000082 RBX: ffff88046548b000 RCX: 0000000000000000
> >> [ 2552.320286] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000018
> >> [ 2552.320286] RBP: ffff88044e533ab8 R08: 0000000000000001 R09: 0000000000000000
> >> [ 2552.320286] R10: ffff88046548b000 R11: 0000000000000001 R12: 0000000000000000
> >> [ 2552.320286] R13: 0000000000000018 R14: 0000000000000000 R15: 0000000000000000
> >> [ 2552.320286] FS:  00007fd286a9a700(0000) GS:ffff88018b000000(0000) knlGS:0000000000000000
> >> [ 2552.320286] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> >> [ 2552.320286] CR2: 0000000000000018 CR3: 0000000442c17000 CR4: 00000000000006a0
> >> [ 2552.320286] DR0: 0000000000695000 DR1: 0000000000000000 DR2: 0000000000000000
> >> [ 2552.320286] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> >> [ 2552.320286] Stack:
> >> [ 2552.320286]  ffff88044e5339e8 ffffffff9f56e761 0000000000000000 ffff880315c13000
> >> [ 2552.320286]  ffff88044e533a38 ffffffff9c193f0d ffffffff9c193e34 ffff8804654e8000
> >> [ 2552.320286]  ffff8804654e8000 0000000000000001 ffff88046548b000 0000000000000007
> >> [ 2552.320286] Call Trace:
> >> [ 2552.320286] ? _raw_spin_unlock_irq (arch/x86/include/asm/preempt.h:98 include/linux/spinlock_api_smp.h:169 kernel/locking/spinlock.c:199)
> >> [ 2552.320286] ? finish_task_switch (include/linux/tick.h:206 kernel/sched/core.c:2163)
> >> [ 2552.320286] ? finish_task_switch (arch/x86/include/asm/current.h:14 kernel/sched/sched.h:993 kernel/sched/core.c:2145)
> >> [ 2552.320286] ? retint_restore_args (arch/x86/kernel/entry_64.S:1040)
> >> [ 2552.320286] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
> >> [ 2552.320286] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2557 kernel/locking/lockdep.c:2599)
> >> [ 2552.320286] lock_acquire (arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602)
> >> [ 2552.320286] ? remove_migration_pte (mm/migrate.c:137)
> >> [ 2552.320286] ? retint_restore_args (arch/x86/kernel/entry_64.S:1040)
> >> [ 2552.320286] _raw_spin_lock (include/linux/spinlock_api_smp.h:143 kernel/locking/spinlock.c:151)
> >> [ 2552.320286] ? remove_migration_pte (mm/migrate.c:137)
> >> [ 2552.320286] remove_migration_pte (mm/migrate.c:137)
> >> [ 2552.320286] rmap_walk (mm/rmap.c:1628 mm/rmap.c:1699)
> >> [ 2552.320286] remove_migration_ptes (mm/migrate.c:224)
> >> [ 2552.320286] ? new_page_node (mm/migrate.c:107)
> >> [ 2552.320286] ? remove_migration_pte (mm/migrate.c:195)
> >> [ 2552.320286] migrate_pages (mm/migrate.c:922 mm/migrate.c:960 mm/migrate.c:1126)
> >> [ 2552.320286] ? perf_trace_mm_numa_migrate_ratelimit (mm/migrate.c:1574)
> >> [ 2552.320286] migrate_misplaced_page (mm/migrate.c:1733)
> >> [ 2552.320286] __handle_mm_fault (mm/memory.c:3762 mm/memory.c:3812 mm/memory.c:3925)
> >> [ 2552.320286] ? __const_udelay (arch/x86/lib/delay.c:126)
> >> [ 2552.320286] ? __rcu_read_unlock (kernel/rcu/update.c:97)
> >> [ 2552.320286] handle_mm_fault (mm/memory.c:3948)
> >> [ 2552.320286] __get_user_pages (mm/memory.c:1851)
> >> [ 2552.320286] ? preempt_count_sub (kernel/sched/core.c:2527)
> >> [ 2552.320286] __mlock_vma_pages_range (mm/mlock.c:255)
> >> [ 2552.320286] __mm_populate (mm/mlock.c:711)
> >> [ 2552.320286] SyS_mlockall (include/linux/mm.h:1799 mm/mlock.c:817 mm/mlock.c:791)
> >> [ 2552.320286] tracesys (arch/x86/kernel/entry_64.S:749)
> >> [ 2552.320286] Code: 85 2d 1e 00 00 48 c7 c1 d7 68 6c a0 48 c7 c2 47 11 6c a0 31 c0 be fa 0b 00 00 48 c7 c7 91 68 6c a0 e8 1c 6d f9 ff e9 07 1e 00 00 <49> 81 7d 00 80 31 76 a2 b8 00 00 00 00 44 0f 44 c0 eb 07 0f 1f
> >> [ 2552.320286] RIP __lock_acquire (kernel/locking/lockdep.c:3070 (discriminator 1))
> >> [ 2552.320286]  RSP <ffff88044e5339c8>
> >> [ 2552.320286] CR2: 0000000000000018

Sasha, please clarify your Ping: I've seen you say in other mail
"I had to disable transhuge/hugetlb in my testing .config".

Do you see this remove_migration_pte oops even with THP disabled?

Do you see the filemap.c:202 BUG_ON(page_mapped(page))
even with THP disabled?

Hugh
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