Message-ID: <m2l28c262361004222211j602f224bv60ffd381f524e78a@mail.gmail.com>
Date:	Fri, 23 Apr 2010 14:11:37 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Mel Gorman <mel@....ul.ie>, Christoph Lameter <cl@...ux.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [BUGFIX][mm][PATCH] fix migration race in rmap_walk

On Fri, Apr 23, 2010 at 12:01 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
>
> This patch itself is for -mm ..but may need to go -stable tree for memory
> hotplug. (but we've got no report to hit this race...)
>
> This one is the simplest, I think and works well on my test set.
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> In rmap.c, at checking rmap in vma chain in page->mapping, anon_vma->lock
> or mapping->i_mmap_lock is held and enter following loop.
>
>        for_each_vma_in_this_rmap_link(list from page->mapping) {
>                unsigned long address = vma_address(page, vma);
>                if (address == -EFAULT)
>                        continue;
>                ....
>        }
>
> vma_address is checking [start, end, pgoff] v.s. page->index.
>
> But vma's [start, end, pgoff] is updated without locks. vma_address()
> can hit a race and may return wrong result.
>
> This bahavior is no problem in usual routine as try_to_unmap() etc...
> But for page migration, rmap_walk() has to find all migration_ptes
> which migration code overwritten valid ptes. This race is critical and cause
> BUG that a migration_pte is sometimes not removed.
>
> pr 21 17:27:47 localhost kernel: ------------[ cut here ]------------
> Apr 21 17:27:47 localhost kernel: kernel BUG at include/linux/swapops.h:105!
> Apr 21 17:27:47 localhost kernel: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
> Apr 21 17:27:47 localhost kernel: last sysfs file: /sys/devices/virtual/net/br0/statistics/collisions
> Apr 21 17:27:47 localhost kernel: CPU 3
> Apr 21 17:27:47 localhost kernel: Modules linked in: fuse sit tunnel4 ipt_MASQUERADE iptable_nat nf_nat bridge stp llc sunrpc cpufreq_ondemand acpi_cpufreq freq_table mperf xt_physdev ip6t_REJECT nf_conntrack_ipv6 ip6table_filter ip6_tables ipv6 dm_multipath uinput ioatdma ppdev parport_pc i5000_edac bnx2 iTCO_wdt edac_core iTCO_vendor_support shpchp parport e1000e kvm_intel dca kvm i2c_i801 i2c_core i5k_amb pcspkr megaraid_sas [last unloaded: microcode]
> Apr 21 17:27:47 localhost kernel:
> Apr 21 17:27:47 localhost kernel: Pid: 27892, comm: cc1 Tainted: G        W   2.6.34-rc4-mm1+ #4 D2519/PRIMERGY
> Apr 21 17:27:47 localhost kernel: RIP: 0010:[<ffffffff8114e9cf>]  [<ffffffff8114e9cf>] migration_entry_wait+0x16f/0x180
> Apr 21 17:27:47 localhost kernel: RSP: 0000:ffff88008d9efe08  EFLAGS: 00010246
> Apr 21 17:27:47 localhost kernel: RAX: ffffea0000000000 RBX: ffffea0000241100 RCX: 0000000000000001
> Apr 21 17:27:47 localhost kernel: RDX: 000000000000a4e0 RSI: ffff880621a4ab00 RDI: 000000000149c03e
> Apr 21 17:27:47 localhost kernel: RBP: ffff88008d9efe38 R08: 0000000000000000 R09: 0000000000000000
> Apr 21 17:27:47 localhost kernel: R10: 0000000000000000 R11: 0000000000000001 R12: ffff880621a4aae8
> Apr 21 17:27:47 localhost kernel: R13: 00000000bf811000 R14: 000000000149c03e R15: 0000000000000000
> Apr 21 17:27:47 localhost kernel: FS:  00007fe6abc90700(0000) GS:ffff880005a00000(0000) knlGS:0000000000000000
> Apr 21 17:27:47 localhost kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> Apr 21 17:27:47 localhost kernel: CR2: 00007fe6a37279a0 CR3: 000000008d942000 CR4: 00000000000006e0
> Apr 21 17:27:47 localhost kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> Apr 21 17:27:47 localhost kernel: DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Apr 21 17:27:47 localhost kernel: Process cc1 (pid: 27892, threadinfo ffff88008d9ee000, task ffff8800b23ec820)
> Apr 21 17:27:47 localhost kernel: Stack:
> Apr 21 17:27:47 localhost kernel: ffffea000101aee8 ffff880621a4aae8 ffff88008d9efe38 00007fe6a37279a0
> Apr 21 17:27:47 localhost kernel: <0> ffff8805d9706d90 ffff880621a4aa00 ffff88008d9efef8 ffffffff81126d05
> Apr 21 17:27:47 localhost kernel: <0> ffff88008d9efec8 0000000000000246 0000000000000000 ffffffff81586533
> Apr 21 17:27:47 localhost kernel: Call Trace:
> Apr 21 17:27:47 localhost kernel: [<ffffffff81126d05>] handle_mm_fault+0x995/0x9b0
> Apr 21 17:27:47 localhost kernel: [<ffffffff81586533>] ? do_page_fault+0x103/0x330
> Apr 21 17:27:47 localhost kernel: [<ffffffff8104bf40>] ? finish_task_switch+0x0/0xf0
> Apr 21 17:27:47 localhost kernel: [<ffffffff8158659e>] do_page_fault+0x16e/0x330
> Apr 21 17:27:47 localhost kernel: [<ffffffff81582f35>] page_fault+0x25/0x30
> Apr 21 17:27:47 localhost kernel: Code: 53 08 85 c9 0f 84 32 ff ff ff 8d 41 01 89 4d d8 89 45 d4 8b 75 d4 8b 45 d8 f0 0f b1 32 89 45 dc 8b 45 dc 39 c8 74 aa 89 c1 eb d7 <0f> 0b eb fe 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5
> Apr 21 17:27:47 localhost kernel: RIP  [<ffffffff8114e9cf>] migration_entry_wait+0x16f/0x180
> Apr 21 17:27:47 localhost kernel: RSP <ffff88008d9efe08>
> Apr 21 17:27:47 localhost kernel: ---[ end trace 4860ab585c1fcddb ]---
>
>
>
> This patch adds vma_address_safe(). And update [start, end, pgoff]
> under seq counter.
>
> Cc: Mel Gorman <mel@....ul.ie>
> Cc: Minchan Kim <minchan.kim@...il.com>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

That's exactly same what I have in mind. :)
But I am hesitating. That's because AFAIR, we try to remove seqlock. Right?
But in this case, seqlock is good, I think. :)
-- 
Kind regards,
Minchan Kim
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