Re: [PATCH] x86: revert "x86: Fix S4 regression"

[Takao Indoh]

(2012/07/25 0:55), Cong Wang wrote:
> On Mon, 2012-07-23 at 20:22 +0900, Takao Indoh wrote:
> > (2012/07/23 19:00), Dave Young wrote:
> > > On 07/17/2012 11:15 AM, Takao Indoh wrote:
> > >
> > > > Hi Cong,
> > > >
> > > > When I tested kdump with 3.5.0-rc6 kernel, I found a problem of kdump
> > > > kernel's panic in find_early_table_space().
> > > >
> > > > init_memory_mapping: [mem 0x00000000-0x36ffafff]
> > > > Kernel panic - not syncing: Cannot find space for the kernel page tables
> > > > Pid: 0, comm: swapper Not tainted 3.5.0-rc6 #17
> > > > Call Trace:
> > > >    [<ffffffff8158549b>] panic+0xb8/0x1c8
> > > >    [<ffffffff8158565d>] ? printk+0x48/0x4a
> > > >    [<ffffffff8157304c>] init_memory_mapping+0x46c/0x530
> > > >    [<ffffffff818a73c7>] setup_arch+0x669/0xb0e
> > > >    [<ffffffff8158565d>] ? printk+0x48/0x4a
> > > >    [<ffffffff818a3a1f>] start_kernel+0x9b/0x34a
> > > >    [<ffffffff818a332d>] x86_64_start_reservations+0x131/0x136
> > > >    [<ffffffff818a341f>] x86_64_start_kernel+0xed/0xf4
> > > >
> > > > In find_early_table_space(), a kernel tries to find free area below 512M
> > > > for pgtable using memblock_find_in_range, but it fails because kdump
> > > > kernel does not have enough free space below 512M due to the memmap
> > > > restriction. This is the memmap option specified against kdump kernel
> > > > when crashkernel=128M.
> > > >
> > > > memmap=560K@64K memmap=130492K@770608K
> > > >
> > > > Only 560KB area is available and it is not sufficient for pgtable (it
> > > > seems that about 1.8MB area is needed for pgtable). This problem is
> > > > fixed by your revert patch. I hope this patch gets merged.
> > >
> > >
> > > I can reproduce this issue as well, probably related to some x86 mm init
> > > commits, this alloc failure does not happen with reverting below commits:
> > >
> > > bd2753b2dda7bb43c7468826de75f49c6a7e8965
> > > 722bc6b16771ed80871e1fd81c86d3627dda2ac8
> > Yeah, my result of bisect is as follows and at first I thought the
> > commit 722bc6 caused this regression.
> >
> > 722bc6b16771ed80871e1fd81c86d3627dda2ac8 is the first bad commit
> > commit 722bc6b16771ed80871e1fd81c86d3627dda2ac8
> > Author: WANG Cong <xiyou.wangcong@xxxxxxxxx>
> > Date:   Mon Mar 5 15:05:13 2012 -0800
> >
> > IIUC, this commit just fixes a bug of counting pgtable entries. As the
> > result, another problem came up to the surface. In the case of my
> > machine(16GB memory), before applying 722bc6, find_early_table_space()
> > requests about 12KB free area and it can be got from 560K@64K area
> > luckily. I think the size find_early_table_space() requests was a bug.
> > After the bug is fixed by the commit 722bc6, find_early_table_space()
> > requires 1.8MB area and it fails as I wrote.
>
> Thanks for tracking this, Takao!
>
> I bet you are using x86_64 not x86 PAE? If so, could you try this patch
> https://patchwork.kernel.org/patch/1195751/
> ? I already reviewed it.

Great, I applied it and now kdump works. Thanks!

Thanks,
Takao Indoh

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