Re: kswapd craziness in 3.7

[Hugh Dickins <hughd@google.com>]

On Mon, 10 Dec 2012, Linus Torvalds wrote:
> [ Adding High Dickins because of the shmem oops. ]

I had already noticed, and was about to reply; but only then refreshed
my mbox window, to find that you've already done it all for me: thanks.

> 
> On Mon, Dec 10, 2012 at 12:35 PM, Zlatko Calusic
> <zlatko.calusic@iskon.hr> wrote:
> >
> > And funny thing that you mention i915, because yesterday my daughter managed to lock up our laptop hard (that was a first), and this is what I found in kern.log after restart:
> >
> > Dec  9 21:29:42 titan vmunix: general protection fault: 0000 [#1] PREEMPT SMP
> > Dec  9 21:29:42 titan vmunix: Modules linked in: vboxpci(O) vboxnetadp(O) vboxnetflt(O) vboxdrv(O) [last unloaded: microcode]
> > Dec  9 21:29:42 titan vmunix: CPU 2
> > Dec  9 21:29:42 titan vmunix: Pid: 2523, comm: Xorg Tainted: G           O 3.7.0-rc8 #1 Hewlett-Packard HP Pavilion dv7 Notebook PC/144B
> > Dec  9 21:29:42 titan vmunix: RIP: 0010:[<ffffffff81090b9c>]  [<ffffffff81090b9c>] find_get_page+0x3c/0x90
> 
> Ho humm..
> 
> I'm not convinced this is related.
> 
> > Dec  9 21:29:42 titan vmunix: Call Trace:
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff81090e21>] find_lock_page+0x21/0x80
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff810a1b60>] shmem_getpage_gfp+0xa0/0x620
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff810a224c>] shmem_read_mapping_page_gfp+0x2c/0x50
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff812b3611>] i915_gem_object_get_pages_gtt+0xe1/0x270
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff812b127f>] i915_gem_object_get_pages+0x4f/0x90
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff812b1383>] i915_gem_object_bind_to_gtt+0xc3/0x4c0
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff812b4413>] i915_gem_object_pin+0x123/0x190
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff812b7d97>] i915_gem_execbuffer_reserve_object.isra.13+0x77/0x190
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff812b8171>] i915_gem_execbuffer_reserve.isra.14+0x2c1/0x320
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff812b87b2>] i915_gem_do_execbuffer.isra.17+0x5e2/0x11b0
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff812b9894>] i915_gem_execbuffer2+0x94/0x280
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff81287de3>] drm_ioctl+0x493/0x530
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff810d9cbf>] do_vfs_ioctl+0x8f/0x530
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff810da1ab>] sys_ioctl+0x4b/0x90
> > Dec  9 21:29:42 titan vmunix:  [<ffffffff8154a4d2>] system_call_fastpath+0x16/0x1b
> >
> > It seems that whenever (if ever?) GFP_NO_KSWAPD removal is attempted again, the i915 driver will need to be taken better care of.
> 
> That decodes to
> 
>   11: e8 89 b7 15 00       callq  0x15b79f  # radix_tree_lookup_slot
>   16: 48 85 c0             test   %rax,%rax
>   19: 48 89 c6             mov    %rax,%rsi
>   1c: 74 41                 je     0x5f
>   1e: 48 8b 18             mov    (%rax),%rbx  #
>   21: 48 85 db             test   %rbx,%rbx
>   24: 74 1f                 je     0x45
>   26: f6 c3 03             test   $0x3,%bl
>   29: 75 3c                 jne    0x67
>   2b:* 8b 53 1c             mov    0x1c(%rbx),%edx     <-- trapping instruction
>   2e: 85 d2                 test   %edx,%edx
>   30: 74 d9                 je     0xb
> 
> where %rbx is 0x0200000000000000. That looks like it could be a
> single-bit error, and should have been zero.
> 
> It's the "atomic_read(&page->counter)" which is part of
> "page_cache_get_speculative()" as far as I can tell, and it's the
> "page" pointer that is that odd (non-pointer) value. The fact that
> %ecx contains the value "-6" makes me wonder if there was a -ENXIO
> somewhere, though.

Yes, just what I was about to say; except I never considered the -6.

I was going to suggest it's a new notebook with not-so-good memory,
but see that Borislav has since made a better suggestion.

> 
> None of it looks all that much related to whether the i915 driver uses
> GFP_NO_KSWAPD or not, though.

Yes, no evidence here of anything to delay 3.7 further.

I'm running on current git, and no problems observed; but then, I never
did see any of these kswapd problems anyway.  And, in particular, I was
unable to reproduce Zlatko's 1GB of 4GB kept free (on yesterday's tree,
with no swap) - I saw about 100MB kept free.

Hugh