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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 02 of 66] mm, migration: Fix race between shift_arg_pages and rmap_walk by guaranteeing rmap_walk finds PTEs created within the temporary stack
Cc: kosaki.motohiro@jp.fujitsu.com, linux-mm@kvack.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
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Hi

> From: Andrea Arcangeli <aarcange@redhat.com>
> 
> Page migration requires rmap to be able to find all migration ptes
> created by migration. If the second rmap_walk clearing migration PTEs
> misses an entry, it is left dangling causing a BUG_ON to trigger during
> fault. For example;
> 
> [  511.201534] kernel BUG at include/linux/swapops.h:105!
> [  511.201534] invalid opcode: 0000 [#1] PREEMPT SMP
> [  511.201534] last sysfs file: /sys/block/sde/size
> [  511.201534] CPU 0
> [  511.201534] Modules linked in: kvm_amd kvm dm_crypt loop i2c_piix4 serio_raw tpm_tis shpchp evdev tpm i2c_core pci_hotplug tpm_bios wmi processor button ext3 jbd mbcache dm_mirror dm_region_hash dm_log dm_snapshot dm_mod raid10 raid456 async_raid6_recov async_pq raid6_pq async_xor xor async_memcpy async_tx raid1 raid0 multipath linear md_mod sg sr_mod cdrom sd_mod ata_generic ahci libahci libata ide_pci_generic ehci_hcd ide_core r8169 mii ohci_hcd scsi_mod floppy thermal fan thermal_sys
> [  511.888526]
> [  511.888526] Pid: 20431, comm: date Not tainted 2.6.34-rc4-mm1-fix-swapops #6 GA-MA790GP-UD4H/GA-MA790GP-UD4H
> [  511.888526] RIP: 0010:[<ffffffff811094ff>]  [<ffffffff811094ff>] migration_entry_wait+0xc1/0x129

Do you mean current linus-tree code is broken? do we need to merge this
ASAP and need to backport stable tree?




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