Crash in -next due to 'mm/vmalloc: replace opencoded 4-level page walkers'

On Fri, Oct 28, 2016 at 10:18:25AM -0700, Guenter Roeck wrote:
> Hi,
> 
> when running sparc64 images in qemu, I see the following crash.
> This is with next-20161028.
> 
> [    2.530785] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff,max_idle_ns: 19112604462750000 ns
> [    2.532359] kernel BUG at mm/memory.c:1881!
> [    2.532798]               \|/ ____ \|/
> [    2.532798]               "@'/ .. \`@"
> [    2.532798]               /_| \__/ |_\
> [    2.532798]                  \__U_/
> [    2.533250] swapper(1): Kernel bad sw trap 5 [#1]
> [    2.533705] CPU: 0 PID: 1 Comm: swapper Not tainted 4.9.0-rc2+ #1
> [    2.534129] task: fffff8001f0af620 task.stack: fffff8001f0b0000
> [    2.534505] TSTATE: 0000004480001605 TPC: 00000000005124d8 TNPC: 00000000005124dc Y: 00000035    Not tainted
> [    2.535112] TPC: <apply_to_page_range+0x2f8/0x3a0>
> [    2.535469] g0: 00000000009b1548 g1: 0000000000a4a990 g2: 0000000000a4a990 g3: 0000000000b37694
> [    2.535857] g4: fffff8001f0af620 g5: 0000000000000000 g6: fffff8001f0b0000 g7: 0000000000000000
> [    2.536236] o0: 000000000000001f o1: 00000000009ac2c0 o2: 0000000000000759 o3: 0000000000122000
> [    2.536695] o4: 0000000000000000 o5: 00000000009ac2c0 sp: fffff8001f0b2d61 ret_pc: 00000000005124d0
> [    2.537086] RPC: <apply_to_page_range+0x2f0/0x3a0>
> [    2.537454] l0: 0000000000000000 l1: 0000000000002000 l2: fffff8001f10b000 l3: 0000000100002000
> [    2.537843] l4: 0000000000aef910 l5: 0000000000a5e7e8 l6: 0000000100001fff l7: ffffffffff800000
> [    2.538229] i0: 0000000000a5e7e8 i1: 0000000100000000 i2: 0000000100002000 i3: 000000000051e5e0
> [    2.538613] i4: fffff8001f0b3708 i5: fffff8001f10c000 i6: fffff8001f0b2e51 i7: 000000000051e8e0
> [    2.539007] I7: <vmap_page_range_noflush+0x40/0x80>
> [    2.539387] Call Trace:
> [    2.539765]  [000000000051e8e0] vmap_page_range_noflush+0x40/0x80
> [    2.540139]  [000000000051e970] map_vm_area+0x50/0x80
> [    2.540492]  [000000000051f84c] __vmalloc_node_range+0x14c/0x260
> [    2.540848]  [000000000051f98c] __vmalloc_node+0x2c/0x40
> [    2.541198]  [00000000004d39cc] bpf_prog_alloc+0x2c/0xa0
> [    2.541554]  [00000000008129bc] bpf_prog_create+0x3c/0xa0
> [    2.541916]  [0000000000adb21c] ptp_classifier_init+0x20/0x4c
> [    2.542271]  [0000000000ad9808] sock_init+0x90/0xa0
> [    2.542622]  [0000000000426cb0] do_one_initcall+0x30/0x160
> [    2.542978]  [0000000000aaeaec] kernel_init_freeable+0x10c/0x1b0
> [    2.543332]  [00000000008e3324] kernel_init+0x4/0x100
> [    2.543681]  [0000000000405f04] ret_from_fork+0x1c/0x2c
> 
> Bisect points to commit 0c79e3331f08 ("mm/vmalloc: replace opencoded 4-level
> page walkers"). Reverting this patch fixes the problem.

Could some mm expert explain why it is safe for mm/vmalloc.c to ignore
huge pud/pmd that raise BUG_ON in the same code in mm/memory.c
(vmap_pmd_range() vs apply_to_pmd_range())?

At a guess, is sparc64 covering the init_mm with a huge zero page? How
is it then meant to be split? Something like

From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 9 Jan 2017 11:37:07 +0000

> Could some mm expert explain why it is safe for mm/vmalloc.c to ignore
> huge pud/pmd that raise BUG_ON in the same code in mm/memory.c
> (vmap_pmd_range() vs apply_to_pmd_range())?
> 
> At a guess, is sparc64 covering the init_mm with a huge zero page? How
> is it then meant to be split? Something like

We map the linear physical area (PAGE_OFFSET --> PAGE_OFFSET +
max_phys_addr) using huge pages unless DEBUG_PAGEALLOC is enabled.

It is not meant to be split, and that's why we don't use huge pages
when DEBUG_PAGEALLOC is set since that requires changes to the mapping
to be possible.
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