Subject: Re: [PATCH] mm: allocate usemap at first instead of mem_map in sparse_init

From: Andrew Morton <[email-masked]>
Date: Wed, 2 Apr 2008 15:52:47 -0700

On Wed, 2 Apr 2008 15:25:48 -0700 Yinghai Lu <[email-masked]> wrote:

> [PATCH] mm: allocate usemap at first instead of mem_map in sparse_init
> 
> on powerpc,
> 
> On Wed, Apr 2, 2008 at 12:22 PM, Badari Pulavarty <[email-masked]> wrote:
> > 
> > On Wed, 2008-04-02 at 18:17 +1100, Michael Ellerman wrote:
> >  > On Wed, 2008-04-02 at 12:38 +0530, Kamalesh Babulal wrote:
> >  > > Andrew Morton wrote:
> >  > > > On Wed, 02 Apr 2008 11:55:36 +0530 Kamalesh Babulal <[email-masked]> wrote:
> >  > > >
> >  > > >> Hi Andrew,
> >  > > >>
> >  > > >> The 2.6.25-rc8-mm1 kernel panic's while bootup on the power machine(s).
> >  > > >>
> >  > > >> [    0.000000] ------------[ cut here ]------------
> >  > > >> [    0.000000] kernel BUG at arch/powerpc/mm/init_64.c:240!
> >  > > >> [    0.000000] Oops: Exception in kernel mode, sig: 5 [#1]
> >  > > >> [    0.000000] SMP NR_CPUS=32 NUMA PowerMac
> >  > > >> [    0.000000] Modules linked in:
> >  > > >> [    0.000000] NIP: c0000000003d1dcc LR: c0000000003d1dc4 CTR: c00000000002b6ac
> >  > > >> [    0.000000] REGS: c00000000049b960 TRAP: 0700   Not tainted  (2.6.25-rc8-mm1-autokern1)
> >  > > >> [    0.000000] MSR: 9000000000021032 <ME,IR,DR>  CR: 44000088  XER: 20000000
> >  > > >> [    0.000000] TASK = c0000000003f9c90[0] 'swapper' THREAD: c000000000498000 CPU: 0
> >  > > >> [    0.000000] GPR00: c0000000003d1dc4 c00000000049bbe0 c0000000004989d0 0000000000000001
> >  > > >> [    0.000000] GPR04: d59aca40f0000000 000000000b000000 0000000000000010 0000000000000000
> >  > > >> [    0.000000] GPR08: 0000000000000004 0000000000000001 c00000027e520800 c0000000004bf0f0
> >  > > >> [    0.000000] GPR12: c0000000004bf020 c0000000003fa900 0000000000000000 0000000000000000
> >  > > >> [    0.000000] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> >  > > >> [    0.000000] GPR20: 0000000000000000 0000000000000000 0000000000000000 4000000001400000
> >  > > >> [    0.000000] GPR24: 00000000017d64b0 c0000000003d6250 0000000000000000 c000000000504000
> >  > > >> [    0.000000] GPR28: 0000000000000000 cf000000001f8000 0000000001000000 cf00000000000000
> >  > > >> [    0.000000] NIP [c0000000003d1dcc] .vmemmap_populate+0xb8/0xf4
> >  > > >> [    0.000000] LR [c0000000003d1dc4] .vmemmap_populate+0xb0/0xf4
> >  > > >> [    0.000000] Call Trace:
> >  > > >> [    0.000000] [c00000000049bbe0] [c0000000003d1dc4] .vmemmap_populate+0xb0/0xf4 (unreliable)
> >  > > >> [    0.000000] [c00000000049bc70] [c0000000003d2ee8] .sparse_mem_map_populate+0x38/0x60
> >  > > >> [    0.000000] [c00000000049bd00] [c0000000003c242c] .sparse_early_mem_map_alloc+0x54/0x94
> >  > > >> [    0.000000] [c00000000049bd90] [c0000000003c250c] .sparse_init+0xa0/0x20c
> >  > > >> [    0.000000] [c00000000049be50] [c0000000003ab7d0] .setup_arch+0x1ac/0x218
> >  > > >> [    0.000000] [c00000000049bee0] [c0000000003a36ac] .start_kernel+0xe0/0x3fc
> >  > > >> [    0.000000] [c00000000049bf90] [c000000000008594] .start_here_common+0x54/0xc0
> >  > > >> [    0.000000] Instruction dump:
> >  > > >> [    0.000000] 7fe3fb78 7ca02a14 4082000c 3860fff4 4800003c e92289c8 e96289c0 e9090002
> >  > > >> [    0.000000] e8eb0002 4bc575cd 60000000 78630fe0 <0b030000> 7ffff214 7fbfe840 7fe3fb78
> >  > > >> [    0.000000] ---[ end trace 31fd0ba7d8756001 ]---
> >  > > >> [    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
> >
> >  mm-make-mem_map-allocation-continuous.patch
> >  and its friends in -mm.
> >  
> >  You have to call sparse_init_one_section() on each pmap and usemap
> >  as we allocate - since valid_section() depends on it (which is needed
> >  by vmemmap_populate() to check if the section is populated or not).
> >  On ppc, we need to call htab_bolted_mapping() on each section and
> >  we need to skip existing sections.
> >  
> >  These patches tried to group all allocations together and then later
> >  calls sparse_init_one_section() - which is not good :(
> 
> so try to allocate usemap at first altogether.

I have to turn all the above crud into a proper changelog.  I'd prefer that
you do it.

Unless this patch should be folded into another one, in which case it
doesn't matter.

> Signed-off-by: Yinghai Lu <[email-masked]>
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index d3cb085..782ebe5 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c

We shouldn't merge this patch on its own because then that will leave a
non-bisectable region in the powerpc history.

So which patch is this patch fixing?  Lexically it applies to
mm-allocate-section_map-for-sparse_init.patch (and its updates).  But is
that where it logically lies?