Re: [4.19.y PATCH] tmpfs: fix unable to remount nr_inodes from limited to unlimited

["yukuai (C)" <yukuai3@huawei.com>]

On 2019/12/5 1:33, Greg KH wrote:
> On Wed, Dec 04, 2019 at 09:11:37PM +0800, yu kuai wrote:
>> tmpfs support 'size', 'nr_blocks' and 'nr_inodes' mount options. mount or
>> remount them to zero means unlimited. 'size' and 'br_blocks' can remount
>> from limited to unlimited, while 'nr_inodes' can't.
>>
>> The problem is fixed since upstream commit 0b5071dd323d ("
>> shmem_parse_options(): use a separate structure to keep the results"). But
>> in order to backport it, the amount of related patches need to backport is
>> huge.
>>
>> So, I made some local changes to fix the problem.
>>
>> Signed-off-by: yu kuai <yukuai3@huawei.com>
>> ---
>>   mm/shmem.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 3c8742655756..966fc69ee8fb 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -3444,7 +3444,7 @@ static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
>>   	inodes = sbinfo->max_inodes - sbinfo->free_inodes;
>>   	if (percpu_counter_compare(&sbinfo->used_blocks, config.max_blocks) > 0)
>>   		goto out;
>> -	if (config.max_inodes < inodes)
>> +	if (config.max_inodes && config.max_inodes < inodes)
>>   		goto out;
>>   	/*
>>   	 * Those tests disallow limited->unlimited while any are in use;
>> @@ -3460,7 +3460,10 @@ static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
>>   	sbinfo->huge = config.huge;
>>   	sbinfo->max_blocks  = config.max_blocks;
>>   	sbinfo->max_inodes  = config.max_inodes;
>> -	sbinfo->free_inodes = config.max_inodes - inodes;
>> +	if (!config.max_inodes)
>> +		sbinfo->free_inodes = 0;
>> +	else
>> +		sbinfo->free_inodes = config.max_inodes - inodes;
>>   
>>   	/*
>>   	 * Preserve previous mempolicy unless mpol remount option was specified.
>> -- 
>> 2.17.2
>>
> 
> Hm, sorry about my bot, this looked like an odd one-off patch.
> 
> What about 5.3.y, should this patch also go there as well?
Yes, 4.4y and 5.3y have the same problem.
> 
> But is it really an issue as this is a new "feature" that 5.4 now has,
> can't you just use 5.4.y if you need this type of thing?  It's never
> worked in the past, right?
> 
It's true that it never worked in the past. I thoult it might be a bug 
because the behavior is not like what the document said.

Thanks for your response.
Yu Kuai