答复: 答复: [PATCH] exfat: use kvmalloc_array/kvfree instead of kmalloc_array/kfree

[gaoming <gaoming20@hihonor.com>]

Ok. Just delete exfat_get_dentry_set modification.
We have checked the mem allocation size really not exceeds one page.

Thanks.

-----邮件原件-----
发件人: Namjae Jeon <linkinjeon@kernel.org> 
发送时间: 2023年7月7日 11:46
收件人: gaoming <gaoming20@hihonor.com>
抄送: Sungjong Seo <sj1557.seo@samsung.com>; open list:EXFAT FILE SYSTEM <linux-fsdevel@vger.kernel.org>; open list <linux-kernel@vger.kernel.org>; fengbaopeng <fengbaopeng@hihonor.com>; gaoxu <gaoxu2@hihonor.com>; wangfei 00014658 <wangfei66@hihonor.com>; shenchen 00013118 <harry.shen@hihonor.com>
主题: Re: 答复: [PATCH] exfat: use kvmalloc_array/kvfree instead of kmalloc_array/kfree

2023-07-07 11:27 GMT+09:00, gaoming <gaoming20@hihonor.com>:
> exfat_get_dentry_set could be called after the u-disk have been 
> inserted, through exfat_find, __exfat_write_inode functions.
> This could happen at any time, which scenario can not guarantee the 
> continuity of physical memory.
> This bugfix will enhance the robustness of exfat.
I'm sorry, but I understood that it was changed even though you didn't find any particular problem. I think there will not be issues like allocation-bitmap allocation failures. I will delete this code and apply it. If you don't agree, please explain how much memory is allocated here.
Thanks.
>
> Thanks.
> -----邮件原件-----
> 发件人: Namjae Jeon <linkinjeon@kernel.org>
> 发送时间: 2023年7月7日 7:10
> 收件人: gaoming <gaoming20@hihonor.com>
> 抄送: Sungjong Seo <sj1557.seo@samsung.com>; open list:EXFAT FILE SYSTEM 
> <linux-fsdevel@vger.kernel.org>; open list 
> <linux-kernel@vger.kernel.org>; fengbaopeng <fengbaopeng@hihonor.com>; 
> gaoxu <gaoxu2@hihonor.com>; wangfei
> 00014658 <wangfei66@hihonor.com>; shenchen 00013118 
> <harry.shen@hihonor.com>
> 主题: Re: [PATCH] exfat: use kvmalloc_array/kvfree instead of 
> kmalloc_array/kfree
>
> 2023-07-05 18:15 GMT+09:00, gaoming <gaoming20@hihonor.com>:
>> The call stack shown below is a scenario in the Linux 4.19 kernel.
>> Allocating memory failed where exfat fs use kmalloc_array due to 
>> system memory fragmentation, while the u-disk was inserted without 
>> recognition.
>> Devices such as u-disk using the exfat file system are pluggable and 
>> may be insert into the system at any time.
>> However, long-term running systems cannot guarantee the continuity of 
>> physical memory. Therefore, it's necessary to address this issue.
>>
>> Binder:2632_6: page allocation failure: order:4, 
>> mode:0x6040c0(GFP_KERNEL|__GFP_COMP), nodemask=(null) Call trace:
>> [242178.097582]  dump_backtrace+0x0/0x4 [242178.097589]
>> dump_stack+0xf4/0x134 [242178.097598]  warn_alloc+0xd8/0x144 
>> [242178.097603]  __alloc_pages_nodemask+0x1364/0x1384
>> [242178.097608]  kmalloc_order+0x2c/0x510 [242178.097612] 
>> kmalloc_order_trace+0x40/0x16c [242178.097618]  __kmalloc+0x360/0x408 
>> [242178.097624]  load_alloc_bitmap+0x160/0x284 [242178.097628] 
>> exfat_fill_super+0xa3c/0xe7c [242178.097635]  mount_bdev+0x2e8/0x3a0 
>> [242178.097638]  exfat_fs_mount+0x40/0x50 [242178.097643]
>> mount_fs+0x138/0x2e8 [242178.097649]  vfs_kern_mount+0x90/0x270 
>> [242178.097655]  do_mount+0x798/0x173c [242178.097659] 
>> ksys_mount+0x114/0x1ac [242178.097665]  __arm64_sys_mount+0x24/0x34 
>> [242178.097671]  el0_svc_common+0xb8/0x1b8 [242178.097676]
>> el0_svc_handler+0x74/0x90 [242178.097681]  el0_svc+0x8/0x340
>>
>> By analyzing the exfat code,we found that continuous physical memory 
>> is not required here,so kvmalloc_array is used can solve this problem.
>>
>> Signed-off-by: gaoming <gaoming20@hihonor.com>
>> ---
>>  fs/exfat/balloc.c | 4 ++--
>>  fs/exfat/dir.c    | 4 ++--
>>  2 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c index
>> 9f42f25fab92..a183558cb7a0 100644
>> --- a/fs/exfat/balloc.c
>> +++ b/fs/exfat/balloc.c
>> @@ -69,7 +69,7 @@ static int exfat_allocate_bitmap(struct super_block 
>> *sb,
>>  	}
>>  	sbi->map_sectors = ((need_map_size - 1) >>
>>  			(sb->s_blocksize_bits)) + 1;
>> -	sbi->vol_amap = kmalloc_array(sbi->map_sectors,
>> +	sbi->vol_amap = kvmalloc_array(sbi->map_sectors,
>>  				sizeof(struct buffer_head *), GFP_KERNEL);
>>  	if (!sbi->vol_amap)
>>  		return -ENOMEM;
>> @@ -84,7 +84,7 @@ static int exfat_allocate_bitmap(struct super_block 
>> *sb,
>>  			while (j < i)
>>  				brelse(sbi->vol_amap[j++]);
>>
>> -			kfree(sbi->vol_amap);
>> +			kvfree(sbi->vol_amap);
>>  			sbi->vol_amap = NULL;
>>  			return -EIO;
>>  		}
>> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c index
>> 957574180a5e..5cbb78d0a2a2 100644
>> --- a/fs/exfat/dir.c
>> +++ b/fs/exfat/dir.c
>> @@ -649,7 +649,7 @@ int exfat_put_dentry_set(struct 
>> exfat_entry_set_cache *es, int sync)
>>  			brelse(es->bh[i]);
>>
>>  	if (IS_DYNAMIC_ES(es))
>> -		kfree(es->bh);
>> +		kvfree(es->bh);
>>
>>  	return err;
>>  }
>> @@ -888,7 +888,7 @@ int exfat_get_dentry_set(struct 
>> exfat_entry_set_cache *es,
>>
>>  	num_bh = EXFAT_B_TO_BLK_ROUND_UP(off + num_entries * DENTRY_SIZE, sb);
>>  	if (num_bh > ARRAY_SIZE(es->__bh)) {
>> -		es->bh = kmalloc_array(num_bh, sizeof(*es->bh), GFP_KERNEL);
>> +		es->bh = kvmalloc_array(num_bh, sizeof(*es->bh), GFP_KERNEL);
> Could you please elaborate why you change this to kvmalloc_array also?
>
> Thanks.
>>  		if (!es->bh) {
>>  			brelse(bh);
>>  			return -ENOMEM;
>> --
>> 2.17.1
>>
>>
>