Re: [PATCH 04/14] mm,migration: Allow the migration ofPageSwapCache pages

[Mel Gorman]

On Tue, Apr 27, 2010 at 07:41:39PM +0900, KAMEZAWA Hiroyuki wrote:
> On Tue, 27 Apr 2010 10:40:02 +0100
> Mel Gorman <mel@xxxxxxxxx> wrote:
> 
> > On Sun, Apr 25, 2010 at 04:41:13PM +0200, Andrea Arcangeli wrote:
> > > On Sat, Apr 24, 2010 at 11:52:27AM +0100, Mel Gorman wrote:
> > > > It should be. I expect that's why you have never seen the bugon in
> > > > swapops.
> > > 
> > > Oh I just got the very crash you're talking about with aa.git with
> > > your v8 code. Weird that I never reproduced it before! I think it's
> > > because I fixed gcc to be fully backed by hugepages always (without
> > > khugepaged) and I was rebuilding a couple of packages, and that now
> > > triggers memory compaction much more, but mixed with heavy
> > > fork/execve. This is the only instability I managed to reproduce over
> > > 24 hours of stress testing and it's clearly not related to transparent
> > > hugepage support but it's either a bug in migrate.c (more likely) or
> > > memory compaction.
> > > 
> > > Note that I'm running with the 2.6.33 anon-vma code, so it will
> > > relieve you to know it's not the anon-vma recent changes causing this
> > > (well I can't rule out anon-vma bugs, but if it's anon-vma, it's a
> > > longstanding one).
> > > 
> > > kernel BUG at include/linux/swapops.h:105!
> > > invalid opcode: 0000 [#1] SMP 
> > > last sysfs file: /sys/devices/pci0000:00/0000:00:12.0/host0/target0:0:0/0:0:0:0/block/sr0/size
> > > CPU 0 
> > > Modules linked in: nls_iso8859_1 loop twofish twofish_common tun bridge stp llc bnep sco rfcomm l2cap bluetooth snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss usbhid gspca_pac207 gspca_main videodev v4l1_compat v4l2_compat_ioctl32 snd_hda_codec_realtek ohci_hcd snd_hda_intel ehci_hcd usbcore snd_hda_codec snd_pcm snd_timer snd snd_page_alloc sg psmouse sr_mod pcspkr
> > > 
> > > Pid: 13351, comm: basename Not tainted 2.6.34-rc5 #23 M2A-VM/System Product Name
> > > RIP: 0010:[<ffffffff810e66b0>]  [<ffffffff810e66b0>] migration_entry_wait+0x170/0x180
> > > RSP: 0000:ffff88009ab6fa58  EFLAGS: 00010246
> > > RAX: ffffea0000000000 RBX: ffffea000234eed8 RCX: ffff8800aaa95298
> > > RDX: 00000000000a168d RSI: ffff88000411ae28 RDI: ffffea00025550a8
> > > RBP: ffffea0002555098 R08: ffff88000411ae28 R09: 0000000000000000
> > > R10: 0000000000000008 R11: 0000000000000009 R12: 00000000aaa95298
> > > R13: 00007ffff8a53000 R14: ffff88000411ae28 R15: ffff88011108a7c0
> > > FS:  00002adf29469b90(0000) GS:ffff880001a00000(0000) knlGS:0000000055700d50
> > > CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > > CR2: 00007ffff8a53000 CR3: 0000000004f80000 CR4: 00000000000006f0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > > Process basename (pid: 13351, threadinfo ffff88009ab6e000, task ffff88009ab96c70)
> > > Stack:
> > > ffff8800aaa95280 ffffffff810ce472 ffff8801134a7ce8 0000000000000000
> > > <0> 00000000142d1a3e ffffffff810c2e35 79f085e9c08a4db7 62d38944fd014000
> > > <0> 76b07a274b0c057a ffffea00025649f8 f8000000000a168d d19934e84d2a74f3
> > > Call Trace:
> > > [<ffffffff810ce472>] ? page_add_new_anon_rmap+0x72/0xc0
> > > [<ffffffff810c2e35>] ? handle_pte_fault+0x7a5/0x7d0
> > > [<ffffffff8150506d>] ? do_page_fault+0x13d/0x420
> > > [<ffffffff8150215f>] ? page_fault+0x1f/0x30
> > > [<ffffffff81273bfb>] ? strnlen_user+0x4b/0x80
> > > [<ffffffff81131f4e>] ? load_elf_binary+0x12be/0x1c80
> > > [<ffffffff810f426d>] ? search_binary_handler+0xad/0x2c0
> > > [<ffffffff810f5ce7>] ? do_execve+0x247/0x320
> > > [<ffffffff8100ab16>] ? sys_execve+0x36/0x60
> > > [<ffffffff8100314a>] ? stub_execve+0x6a/0xc0
> > > Code: 5e ff ff ff 8d 41 01 89 4c 24 08 89 44 24 04 8b 74 24 04 8b 44 24 08 f0 0f b1 32 89 44 24 0c 8b 44 24 0c 39 c8 74 a4 89 c1 eb d1 <0f> 0b eb fe 66 66 66 2e 0f 1f 84 00 00 00 00 00 41 54 49 89 d4 
> > > RIP  [<ffffffff810e66b0>] migration_entry_wait+0x170/0x180
> > > RSP <ffff88009ab6fa58>
> > > ---[ end trace 840ce8bc6f6dc402 ]---
> > > 
> > > It doesn't look like a coincidence the page that had the migration PTE
> > > set was the argv in the user stack during execve. The bug has to be
> > > there. Or maybe it's a coincidence and it will mislead us. If you've
> > > other stack traces please post them so I can have more info (I'll post
> > > more stack traces if I get them again, it doesn't look easy to
> > > reproduce, supposedly the bug has always been there since the first
> > > time I used memory compaction, and this is the first time I reproduce
> > > it).
> > > 
> > 
> > The oopses I am getting look very similar. The page is encountered in
> > the stack while copying the arguements in. I don't think it's a
> > coincidence.
> > 
> 
> Hmm. booby trap aronude here ?

I think so. I have a debugging patch running at the moment that is
checking for migration ptes while the page tables are being moved.

> ==
> static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
> {
> ....
>        /*
>          * cover the whole range: [new_start, old_end)
>          */
>         if (vma_adjust(vma, new_start, old_end, vma->vm_pgoff, NULL))
>                 return -ENOMEM;
> 
>         /*
>          * move the page tables downwards, on failure we rely on
>          * process cleanup to remove whatever mess we made.
>          */
>         if (length != move_page_tables(vma, old_start,
>                                        vma, new_start, length))
>                 return -ENOMEM;
> ...

Specfically, I have it in move_ptes. If migration entries are being found
there, it would be reasonable for exec() to wait on migration to complete
but what you suggest below is more plausible.

>         /*
>          * Shrink the vma to just the new range.  Always succeeds.
>          */
>         vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL);
> 
> 	
> ==
> 
> I think we have wrong vma_address() -> "pte"
> ==
> 	=== (A) ===
> 	vma_adjust().  ---- (*)
> 	=== (B) ===
> 	move_pte().
> ==
> 
> 	vma_address(page, vma)
> 	=> address = vma->vm_start + ((page->index << shift) - vma->vm_pgoff) << PAGE_SHIFT);
> 
> So, vma_address() in zone (A) and vma_address in (B) will return different address.
> 

Yes. I was expecting that the anon_vma lock in vma_adjust would delay exec
until migration completed.

> When pte inludes migration_pte, this seems critical. Because an address pointed
> by vma_address() in zone (B) will not contain migration_pte until
> move_ptes() ends.
> 

This is plausible considering that, like vma_adjust(), move_ptes does
not appear to take the anon_vma->lock in the same fashion as i_mmap_lock
is taken for files.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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