linux-kernel - Re: [PATCH] mm/zsmalloc: include sparsemem.h for MAX_PHYSMEM

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Date:   Tue, 10 Nov 2020 10:29:54 +0100
From:   Stefan Agner <stefan@...er.ch>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     minchan@...nel.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com, akpm@...ux-foundation.org,
        sjenning@...ux.vnet.ibm.com, gregkh@...uxfoundation.org,
        arnd@...db.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/zsmalloc: include sparsemem.h for MAX_PHYSMEM_BITS

On 2020-11-08 07:46, Mike Rapoport wrote:
> On Sat, Nov 07, 2020 at 04:22:06PM +0100, Stefan Agner wrote:
>> Most architectures define MAX_PHYSMEM_BITS in asm/sparsemem.h and don't
>> include it in asm/pgtable.h. Include asm/sparsemem.h directly to get
>> the MAX_PHYSMEM_BITS define on all architectures.
>>
>> This fixes a crash when accessing zram on 32-bit ARM platform with LPAE and
>> more than 4GB of memory:
>>   Unable to handle kernel NULL pointer dereference at virtual address 00000000
>>   pgd = a27bd01c
>>   [00000000] *pgd=236a0003, *pmd=1ffa64003
>>   Internal error: Oops: 207 [#1] SMP ARM
>>   Modules linked in: mdio_bcm_unimac(+) brcmfmac cfg80211 brcmutil raspberrypi_hwmon hci_uart crc32_arm_ce bcm2711_thermal phy_generic genet
>>   CPU: 0 PID: 123 Comm: mkfs.ext4 Not tainted 5.9.6 #1
>>   Hardware name: BCM2711
>>   PC is at zs_map_object+0x94/0x338
>>   LR is at zram_bvec_rw.constprop.0+0x330/0xa64
>>   pc : [<c0602b38>]    lr : [<c0bda6a0>]    psr: 60000013
>>   sp : e376bbe0  ip : 00000000  fp : c1e2921c
>>   r10: 00000002  r9 : c1dda730  r8 : 00000000
>>   r7 : e8ff7a00  r6 : 00000000  r5 : 02f9ffa0  r4 : e3710000
>>   r3 : 000fdffe  r2 : c1e0ce80  r1 : ebf979a0  r0 : 00000000
>>   Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
>>   Control: 30c5383d  Table: 235c2a80  DAC: fffffffd
>>   Process mkfs.ext4 (pid: 123, stack limit = 0x495a22e6)
>>   Stack: (0xe376bbe0 to 0xe376c000)
>>   ...
>>   [<c0602b38>] (zs_map_object) from [<c0bda6a0>] (zram_bvec_rw.constprop.0+0x330/0xa64)
>>   [<c0bda6a0>] (zram_bvec_rw.constprop.0) from [<c0bdaf78>] (zram_submit_bio+0x1a4/0x40c)
>>   [<c0bdaf78>] (zram_submit_bio) from [<c085806c>] (submit_bio_noacct+0xd0/0x3c8)
>>   [<c085806c>] (submit_bio_noacct) from [<c08583b0>] (submit_bio+0x4c/0x190)
>>   [<c08583b0>] (submit_bio) from [<c06496b4>] (submit_bh_wbc+0x188/0x1b8)
>>   [<c06496b4>] (submit_bh_wbc) from [<c064ce98>] (__block_write_full_page+0x340/0x5e4)
>>   [<c064ce98>] (__block_write_full_page) from [<c064d3ec>] (block_write_full_page+0x128/0x170)
>>   [<c064d3ec>] (block_write_full_page) from [<c0591ae8>] (__writepage+0x14/0x68)
>>   [<c0591ae8>] (__writepage) from [<c0593efc>] (write_cache_pages+0x1bc/0x494)
>>   [<c0593efc>] (write_cache_pages) from [<c059422c>] (generic_writepages+0x58/0x8c)
>>   [<c059422c>] (generic_writepages) from [<c0594c24>] (do_writepages+0x48/0xec)
>>   [<c0594c24>] (do_writepages) from [<c0589330>] (__filemap_fdatawrite_range+0xf0/0x128)
>>   [<c0589330>] (__filemap_fdatawrite_range) from [<c05894bc>] (file_write_and_wait_range+0x48/0x98)
>>   [<c05894bc>] (file_write_and_wait_range) from [<c064f3f8>] (blkdev_fsync+0x1c/0x44)
>>   [<c064f3f8>] (blkdev_fsync) from [<c064408c>] (do_fsync+0x3c/0x70)
>>   [<c064408c>] (do_fsync) from [<c0400374>] (__sys_trace_return+0x0/0x2c)
>>   Exception stack(0xe376bfa8 to 0xe376bff0)
>>   bfa0:                   0003d2e0 b6f7b6f0 00000003 00046e40 00001000 00000000
>>   bfc0: 0003d2e0 b6f7b6f0 00000000 00000076 00000000 00000000 befcbb20 befcbb28
>>   bfe0: b6f4e060 befcbad8 b6f23e0c b6dc4a80
>>   Code: e5927000 e0050391 e0871005 e5918018 (e5983000)
>>
>> Fixes: 61989a80fb3a ("staging: zsmalloc: zsmalloc memory allocation library")
>> Signed-off-by: Stefan Agner <stefan@...er.ch>
>> ---
>>  mm/zsmalloc.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>> index c36fdff9a371..260bd48aacd0 100644
>> --- a/mm/zsmalloc.c
>> +++ b/mm/zsmalloc.c
>> @@ -40,6 +40,7 @@
>>  #include <linux/string.h>
>>  #include <linux/slab.h>
>>  #include <linux/pgtable.h>
>> +#include <asm/sparsemem.h>
> 
> asm/sparsemem.h is not available on some architectures.
> It's better to use linux/mmzone.h instead.
> 

Hm, linux/mmzone.h only includes asm/sparsemem.h when CONFIG_SPARSEMEM
is enabled. However, on ARM at least I can have configurations without
CONFIG_SPARSEMEM and physical address extension on (e.g.
multi_v7_defconfig + CONFIG_LPAE + CONFIG_ZSMALLOC).

While sparsemem seems to be a good idea with LPAE it really seems not
required (see also https://lore.kernel.org/patchwork/patch/567589/).

There seem to be also other architectures which define MAX_PHYSMEM_BITS
only when SPARSEMEM is enabled, e.g.
arch/riscv/include/asm/sparsemem.h...

Not sure how to get out of this.. Maybe make ZSMALLOC dependent on
SPARSEMEM? It feels a bit silly restricting ZSMALLOC selection only due
to a compile time define...

--
Stefan

>>  #include <asm/tlbflush.h>
>>  #include <linux/cpumask.h>
>>  #include <linux/cpu.h>
>> --
>> 2.29.1
>>
>>