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Subject: Re: [PATCH v4] Revert "f2fs crypto: avoid unneeded memory allocation
 in ->readdir"
To:     Jaegeuk Kim <jaegeuk@kernel.org>,
        Yunlong Song <yunlong.song@huawei.com>
CC:     <chao@kernel.org>, <yunlong.song@icloud.com>, <miaoxie@huawei.com>,
        <bintian.wang@huawei.com>, <shengyong1@huawei.com>,
        <heyunlei@huawei.com>, <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>
References: <1519463698-60555-1-git-send-email-yunlong.song@huawei.com>
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From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <c36a6024-209c-b660-ba61-e681a98e6f3b@huawei.com>
Date:   Wed, 28 Feb 2018 17:50:48 +0800
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Hi Jaegeuk,

On 2018/2/28 13:48, Jaegeuk Kim wrote:
> Hi Yunlong,
> 
> As Eric pointed out, how do you think using nohighmem for directory likewise

I'd like to ask, at the beginning, why we choose to use highmem for dentry page?
any history reason there?

> ext4, which looks like more efficient? Actually, we don't need to do this in
> most of recent kernels, right?

It's OK to me to keep a line with ext4.

Thanks,

> 
> Thanks,
> 
> On 02/28, Yunlong Song wrote:
>> This reverts commit e06f86e61d7a67fe6e826010f57aa39c674f4b1b.
>>
>> Conflicts:
>> 	fs/f2fs/dir.c
>>
>> In some platforms (such as arm), high memory is used, then the
>> decrypting filename will cause panic, the reason see commit
>> 569cf1876a32e574ba8a7fb825cd91bafd003882 ("f2fs crypto: allocate buffer
>> for decrypting filename"):
>>
>>  We got dentry pages from high_mem, and its address space directly goes into the
>>  decryption path via f2fs_fname_disk_to_usr.
>>  But, sg_init_one assumes the address is not from high_mem, so we can get this
>>  panic since it doesn't call kmap_high but kunmap_high is triggered at the end.
>>
>>  kernel BUG at ../../../../../../kernel/mm/highmem.c:290!
>>  Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
>>  ...
>>   (kunmap_high+0xb0/0xb8) from [<c0114534>] (__kunmap_atomic+0xa0/0xa4)
>>   (__kunmap_atomic+0xa0/0xa4) from [<c035f028>] (blkcipher_walk_done+0x128/0x1ec)
>>   (blkcipher_walk_done+0x128/0x1ec) from [<c0366c24>] (crypto_cbc_decrypt+0xc0/0x170)
>>   (crypto_cbc_decrypt+0xc0/0x170) from [<c0367148>] (crypto_cts_decrypt+0xc0/0x114)
>>   (crypto_cts_decrypt+0xc0/0x114) from [<c035ea98>] (async_decrypt+0x40/0x48)
>>   (async_decrypt+0x40/0x48) from [<c032ca34>] (f2fs_fname_disk_to_usr+0x124/0x304)
>>   (f2fs_fname_disk_to_usr+0x124/0x304) from [<c03056fc>] (f2fs_fill_dentries+0xac/0x188)
>>   (f2fs_fill_dentries+0xac/0x188) from [<c03059c8>] (f2fs_readdir+0x1f0/0x300)
>>   (f2fs_readdir+0x1f0/0x300) from [<c0218054>] (vfs_readdir+0x90/0xb4)
>>   (vfs_readdir+0x90/0xb4) from [<c0218418>] (SyS_getdents64+0x64/0xcc)
>>   (SyS_getdents64+0x64/0xcc) from [<c0105ba0>] (ret_fast_syscall+0x0/0x30)
>>
>> Howerver, later patch:
>> commit e06f86e61d7a ("f2fs crypto: avoid unneeded memory allocation in ->readdir")
>> reverts the codes, which causes panic again in arm, so fix it back to the old version.
>>
>> Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
>> Reviewed-by: Chao Yu <yuchao0@huawei.com>
>> ---
>>  fs/f2fs/dir.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
>> index f00b5ed..de2e295 100644
>> --- a/fs/f2fs/dir.c
>> +++ b/fs/f2fs/dir.c
>> @@ -825,9 +825,16 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
>>  			int save_len = fstr->len;
>>  			int err;
>>  
>> +			de_name.name = f2fs_kmalloc(sbi, de_name.len, GFP_NOFS);
>> +			if (!de_name.name)
>> +				return -ENOMEM;
>> +
>> +			memcpy(de_name.name, d->filename[bit_pos], de_name.len);
>> +
>>  			err = fscrypt_fname_disk_to_usr(d->inode,
>>  						(u32)de->hash_code, 0,
>>  						&de_name, fstr);
>> +			kfree(de_name.name);
>>  			if (err)
>>  				return err;
>>  
>> -- 
>> 1.8.5.2
> 
> .
>