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SubjectRe: [PATCH -next v2 1/6] ext4: init seq with random value in kmmpd
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On 2021/10/7 20:26, Jan Kara wrote:
> On Sat 11-09-21 17:00:54, Ye Bin wrote:
>> If two host has the same nodename, and seq start from 0, May cause the
>> detection mechanism to fail.
>> So init seq with random value to accelerate conflict detection.
>>
>> Signed-off-by: Ye Bin <yebin10@huawei.com>
> Thanks for the patch. I agree the code in kmmpd looks suspicious. The
> sequence number is initialized to a random number in
> ext4_multi_mount_protect() which is called before kmmpd is started. I think
> kmmpd() should initialize its 'seq' to a number fetched from the mmp
> block, instead of 0 as is currently in the code. I don't think generating a
> new random number as you do is really needed...
>
> Honza
Thank you for your advice,i will fix it.
>
>> ---
>> fs/ext4/mmp.c | 32 ++++++++++++++++----------------
>> 1 file changed, 16 insertions(+), 16 deletions(-)
>>
>> diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
>> index cebea4270817..12af6dc8457b 100644
>> --- a/fs/ext4/mmp.c
>> +++ b/fs/ext4/mmp.c
>> @@ -122,6 +122,21 @@ void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
>> (int)sizeof(mmp->mmp_bdevname), mmp->mmp_bdevname);
>> }
>>
>> +/*
>> + * Get a random new sequence number but make sure it is not greater than
>> + * EXT4_MMP_SEQ_MAX.
>> + */
>> +static unsigned int mmp_new_seq(void)
>> +{
>> + u32 new_seq;
>> +
>> + do {
>> + new_seq = prandom_u32();
>> + } while (new_seq > EXT4_MMP_SEQ_MAX);
>> +
>> + return new_seq;
>> +}
>> +
>> /*
>> * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
>> */
>> @@ -132,7 +147,7 @@ static int kmmpd(void *data)
>> struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh;
>> struct mmp_struct *mmp;
>> ext4_fsblk_t mmp_block;
>> - u32 seq = 0;
>> + u32 seq = mmp_new_seq();
>> unsigned long failed_writes = 0;
>> int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
>> unsigned mmp_check_interval;
>> @@ -258,21 +273,6 @@ void ext4_stop_mmpd(struct ext4_sb_info *sbi)
>> }
>> }
>>
>> -/*
>> - * Get a random new sequence number but make sure it is not greater than
>> - * EXT4_MMP_SEQ_MAX.
>> - */
>> -static unsigned int mmp_new_seq(void)
>> -{
>> - u32 new_seq;
>> -
>> - do {
>> - new_seq = prandom_u32();
>> - } while (new_seq > EXT4_MMP_SEQ_MAX);
>> -
>> - return new_seq;
>> -}
>> -
>> /*
>> * Protect the filesystem from being mounted more than once.
>> */
>> --
>> 2.31.1
>>

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