Re: [PATCH] files: rcu free files_struct

[Eric W. Biederman]

Matthew Wilcox <willy@xxxxxxxxxxxxx> writes:

> On Wed, Dec 09, 2020 at 12:04:38PM -0600, Eric W. Biederman wrote:
>> @@ -397,8 +397,9 @@ static struct fdtable *close_files(struct files_struct * files)
>>  		set = fdt->open_fds[j++];
>>  		while (set) {
>>  			if (set & 1) {
>> -				struct file * file = xchg(&fdt->fd[i], NULL);
>> +				struct file * file = fdt->fd[i];
>>  				if (file) {
>> +					rcu_assign_pointer(fdt->fd[i], NULL);
>
> Assuming this is safe, you can use RCU_INIT_POINTER() here because you're
> storing NULL, so you don't need the wmb() before storing the pointer.

Thanks.  I was remembering there was a special case like and I had
forgotten what the rule was.

Eric