Re: [PATCH 04/12] mips: Reserve memory for the kernel image resources

From: Mike Rapoport
Date: Wed May 22 2019 - 04:10:56 EST

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On Wed, May 22, 2019 at 09:47:04AM +0200, Geert Uytterhoeven wrote:
> Hi Mike,
>
> On Tue, May 21, 2019 at 5:53 PM Mike Rapoport <rppt@xxxxxxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxx>
> > >
> > > 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
> > > [...]
> > >
> > > CONFIG_RELOCATABLE is not set, so the only relevant part is the
> > > change quoted below.
> > >
> > > > --- a/arch/mips/kernel/setup.c
> > > > +++ b/arch/mips/kernel/setup.c
> > > > @@ -371,7 +371,6 @@ static void __init bootmem_init(void)
> > > >
> > > > static void __init bootmem_init(void)
> > > > {
> > > > - unsigned long reserved_end;
> > > > phys_addr_t ramstart = PHYS_ADDR_MAX;
> > > > int i;
> > > >
> > > > @@ -382,10 +381,10 @@ static void __init bootmem_init(void)
> > > > * will reserve the area used for the initrd.
> > > > */
> > > > init_initrd();
> > > > - reserved_end = (unsigned long) PFN_UP(__pa_symbol(&_end));
> > > >
> > > > - memblock_reserve(PHYS_OFFSET,
> > > > - (reserved_end << PAGE_SHIFT) - PHYS_OFFSET);
> > > > + /* Reserve memory occupied by kernel. */
> > > > + memblock_reserve(__pa_symbol(&_text),
> > > > + __pa_symbol(&_end) - __pa_symbol(&_text));
> > > >
> > > > /*
> > > > * max_low_pfn is not a number of pages. The number of pages
> > >
> > > With some debug code added:
> > >
> > > Determined physical RAM map:
> > > memory: 08000000 @ 00000000 (usable)
> > > bootmem_init:390: PHYS_OFFSET = 0x0
> > > bootmem_init:391: __pa_symbol(&_text) = 0x100000
> > > bootmem_init:392: __pa_symbol(&_end) = 0x4b77c8
> > > bootmem_init:393: PFN_UP(__pa_symbol(&_end)) = 0x4b8
> >
> > Have you tried adding memblock=debug to the command line?
> > Not sure it'll help, but still :)
>
> Thanks! Output below...
>
> Determined physical RAM map:
> memory: 08000000 @ 00000000 (usable)
> +memblock_reserve: [0x00100000-0x004b77c7] setup_arch+0x258/0x8e4
> Initrd not found or empty - disabling initrd
> +memblock_reserve: [0x00448000-0x00447fff] setup_arch+0x5ac/0x8e4
> +MEMBLOCK configuration:
> + memory size = 0x08000000 reserved size = 0x003b77c8
> + memory.cnt = 0x1
> + memory[0x0] [0x00000000-0x07ffffff], 0x08000000 bytes on node 0 flags: 0x0
> + reserved.cnt = 0x1
> + reserved[0x0] [0x00100000-0x004b77c7], 0x003b77c8 bytes flags: 0x0
> +memblock_alloc_try_nid: 32 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 setup_arch+0x7ec/0x8e4
> +memblock_reserve: [0x004b77e0-0x004b77ff] memblock_alloc_range_nid+0x130/0x178
> Primary instruction cache 32kB, VIPT, 4-way, linesize 32 bytes.
> Primary data cache 32kB, 4-way, VIPT, cache aliases, linesize 32 bytes
> Zone ranges:
> @@ -16,10 +26,48 @@ Movable zone start for each node
> Early memory node ranges
> node 0: [mem 0x0000000000000000-0x0000000007ffffff]
> Initmem setup node 0 [mem 0x0000000000000000-0x0000000007ffffff]
> +memblock_alloc_try_nid: 1048576 bytes align=0x20 nid=0
> from=0x00000000 max_addr=0x00000000
> alloc_node_mem_map.constprop.31+0x6c/0xc8
> +memblock_reserve: [0x004b7800-0x005b77ff] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 16 bytes align=0x20 nid=0 from=0x00000000
> max_addr=0x00000000 setup_usemap.isra.13+0x68/0xa0
> +memblock_reserve: [0x005b7800-0x005b780f] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 116 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 start_kernel+0xb0/0x508
> +memblock_reserve: [0x005b7820-0x005b7893] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 116 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 start_kernel+0xf0/0x508
> +memblock_reserve: [0x005b78a0-0x005b7913] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 116 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 start_kernel+0x114/0x508
> +memblock_reserve: [0x005b7920-0x005b7993] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 4096 bytes align=0x1000 nid=-1
> from=0x00000000 max_addr=0x00000000 pcpu_alloc_alloc_info+0x60/0xb8
> +memblock_reserve: [0x005b8000-0x005b8fff] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 32768 bytes align=0x1000 nid=-1
> from=0x01000000 max_addr=0x00000000 setup_per_cpu_areas+0x38/0xa8
> +memblock_reserve: [0x01000000-0x01007fff] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 4 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_setup_first_chunk+0x200/0x588
> +memblock_reserve: [0x005b79a0-0x005b79a3] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 4 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_setup_first_chunk+0x22c/0x588
> +memblock_reserve: [0x005b79c0-0x005b79c3] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 4 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_setup_first_chunk+0x250/0x588
> +memblock_reserve: [0x005b79e0-0x005b79e3] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 4 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_setup_first_chunk+0x288/0x588
> +memblock_reserve: [0x005b7a00-0x005b7a03] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 120 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_setup_first_chunk+0x47c/0x588
> +memblock_reserve: [0x005b7a20-0x005b7a97] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 89 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_alloc_first_chunk+0x88/0x2e0
> +memblock_reserve: [0x005b7aa0-0x005b7af8] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 1024 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_alloc_first_chunk+0xd8/0x2e0
> +memblock_reserve: [0x005b7b00-0x005b7eff] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 1028 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_alloc_first_chunk+0x118/0x2e0
> +memblock_reserve: [0x005b9000-0x005b9403] memblock_alloc_range_nid+0x130/0x178
> +memblock_alloc_try_nid: 256 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 pcpu_alloc_first_chunk+0x154/0x2e0
> +memblock_reserve: [0x005b7f00-0x005b7fff] memblock_alloc_range_nid+0x130/0x178
> + memblock_free: [0x005b8000-0x005b8fff] start_kernel+0x164/0x508
> Built 1 zonelists, mobility grouping on. Total pages: 32512
> -Kernel command line: console=ttyS0,9600 ip=on root=/dev/nfs rw
> nfsroot=192.168.97.29:/nas/rbtx4927/debian-mipsel,tcp,v3
> +Kernel command line: console=ttyS0,9600 ip=on root=/dev/nfs rw
> nfsroot=192.168.97.29:/nas/rbtx4927/debian-mipsel,tcp,v3
> memblock=debug
> +memblock_alloc_try_nid: 65536 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 alloc_large_system_hash+0x270/0x478
> +memblock_reserve: [0x005b9420-0x005c941f] memblock_alloc_range_nid+0x130/0x178
> Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
> +memblock_alloc_try_nid: 32768 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 alloc_large_system_hash+0x270/0x478
> +memblock_reserve: [0x005c9420-0x005d141f] memblock_alloc_range_nid+0x130/0x178
> Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
> +memblock_reserve: [0x00000000-0x000003ff] trap_init+0x58/0x474
> Memory: 126100K/131072K available (2830K kernel code, 147K rwdata,
> 508K rodata, 220K init, 93K bss, 4972K reserved, 0K cma-reserved)

Presuming your system is !cpu_has_mips_r2_r6 and CAC_BASE is 0 the log
looks completely sane

> > > Hence the old code reserved 1 MiB extra at the beginning.
> > >
> > > Note that the new code also dropped the rounding up of the memory block
> > > size to a multiple of PAGE_SIZE. I'm not sure the latter actually
> > > matters or not.
> >
> > I'd say that bad page state for pfn 1 is caused by "freeing" the first 1M.
>
> Yes, by prom_free_prom_memory(), as pointed out by Serge.

I wonder how other MIPS variants would react to the fact that the memory
below the kernel is not reserved ;-)

> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> 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
>

--
Sincerely yours,
Mike.

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