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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 22 May 2019 09:50:17 +0200
Message-ID: <CAMuHMdUr297MbGqSO+N1NeYbqQsqfLBVFeFMA6epFGQA5V+X+w@mail.gmail.com>
Subject: Re: [PATCH 04/12] mips: Reserve memory for the kernel image resources
To:     Serge Semin <fancer.lancer@gmail.com>
Cc:     Mike Rapoport <rppt@linux.ibm.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@mips.com>,
        James Hogan <jhogan@kernel.org>,
        Matt Redfearn <matt.redfearn@mips.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Bogendoerfer <tbogendoerfer@suse.de>,
        Huacai Chen <chenhc@lemote.com>,
        Stefan Agner <stefan@agner.ch>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Juergen Gross <jgross@suse.com>, linux-mips@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Atsushi Nemoto <anemo@mba.ocn.ne.jp>
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Hi Serge,

On Tue, May 21, 2019 at 6:39 PM Serge Semin <fancer.lancer@gmail.com> wrote:
> On Tue, May 21, 2019 at 06:53:10PM +0300, Mike Rapoport wrote:
> > On Tue, May 21, 2019 at 04:56:39PM +0200, Geert Uytterhoeven wrote:
> > > On Wed, Apr 24, 2019 at 12:50 AM Serge Semin <fancer.lancer@gmail.com> wrote:
> > > > The reserved_end variable had been used by the bootmem_init() code
> > > > to find a lowest limit of memory available for memmap blob. The original
> > > > code just tried to find a free memory space higher than kernel was placed.
> > > > This limitation seems justified for the memmap ragion search process, but
> > > > I can't see any obvious reason to reserve the unused space below kernel
> > > > seeing some platforms place it much higher than standard 1MB. Moreover
> > > > the RELOCATION config enables it to be loaded at any memory address.
> > > > So lets reserve the memory occupied by the kernel only, leaving the region
> > > > below being free for allocations. After doing this we can now discard the
> > > > code freeing a space between kernel _text and VMLINUX_LOAD_ADDRESS symbols
> > > > since it's going to be free anyway (unless marked as reserved by
> > > > platforms).
> > > >
> > > > Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
> > >
> > > This is now commit b93ddc4f9156205e ("mips: Reserve memory for the kernel
> > > image resources") in v5.2-rc1, which causes rbtx4927 to crash during boot:
> > >
> > >     VFS: Mounted root (nfs filesystem) on device 0:13.
> > >     devtmpfs: mounted
> > >     BUG: Bad page state in process swapper  pfn:00001
> > >     page:804b7820 refcount:0 mapcount:-128 mapping:00000000 index:0x1
> > >     flags: 0x0()
> > >     raw: 00000000 00000100 00000200 00000000 00000001 00000000 ffffff7f 00000000
> > >     page dumped because: nonzero mapcount
> > >     Modules linked in:
> > >     CPU: 0 PID: 1 Comm: swapper Not tainted
> > > 5.2.0-rc1-rbtx4927-00468-g3c05ea3d4077b756-dirty #137
> > >     Stack : 00000000 10008400 8040dd2c 87c1b974 8044af63 8040dd2c
> > > 00000001 804a3490
> > >             00000001 81000000 0030f231 80148558 00000003 10008400
> > > 87c1dd80 7599ee13
> > >             00000000 00000000 804b0000 00000000 00000007 00000000
> > > 00000085 00000000
> > >             62722d31 00000084 804b0000 39347874 00000000 804b7820
> > > 8040cef8 81000010
> > >             00000001 00000007 00000001 81000000 00000008 8021de24
> > > 00000000 804a0000
> > >             ...
> > >     Call Trace:
> > >     [<8010adec>] show_stack+0x74/0x104
> > >     [<801a5e44>] bad_page+0x130/0x138
> > >     [<801a654c>] free_pcppages_bulk+0x17c/0x3b0
> > >     [<801a789c>] free_unref_page+0x40/0x68
> > >     [<801120f4>] free_init_pages+0xec/0x104
> > >     [<803bdde8>] free_initmem+0x10/0x58
> > >     [<803bdb8c>] kernel_init+0x20/0x100
> > >     [<801057c8>] ret_from_kernel_thread+0x14/0x1c
> > >     Disabling lock debugging due to kernel taint
> > >     BUG: Bad page state in process swapper  pfn:00002
> > >     [...]
> > >
>
> The root cause of the problem most likely is in prom_free_prom_memory() method of
> arch/mips/txx9/generic/setup.c:
> void __init prom_free_prom_memory(void)
> {
>         unsigned long saddr = PAGE_SIZE;
>         unsigned long eaddr = __pa_symbol(&_text);
>
>         if (saddr < eaddr)
>                 free_init_pages("prom memory", saddr, eaddr);
> }
>
> As you can see the txx9 platform tries to free a memory which isn't reserved
> and set free from the very beginning due to the patch above. So as soon as you
> remove the free_init_pages("prom memory", ...) the problem shall be fixed.
> Could you try it and send a result to us whether it helped?

Thanks, that does the trick!
Will send a patch shortly...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds