[Devel] [PATCH] fuse kio: Add comment about why we need to wait pending read requests

[Kirill Tkhai]

On 23.10.2018 13:15, Pavel Butsykin wrote:
> 
> 
> On 23.10.2018 13:01, Kirill Tkhai wrote:
>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>> ---
>>   fs/fuse/kio/pcs/pcs_fuse_kdirect.c |    7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/fuse/kio/pcs/pcs_fuse_kdirect.c b/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
>> index 3940d6c255ba..9b45fcbf8941 100644
>> --- a/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
>> +++ b/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
>> @@ -1081,7 +1081,12 @@ static void pcs_kio_setattr_handle(struct fuse_inode *fi, struct fuse_req *req)
>>   	r->end = req->end;
>>   	if (di->size.op == PCS_SIZE_SHRINK) {
>>   		BUG_ON(!mutex_is_locked(&req->io_inode->i_mutex));
>> -		/* wait for aio reads in flight */
>> +		/*
>> +		 * Wait for already submitted aio reads. Further reads
>> +		 * (including already queued to bg_queue) will be stopped
>> +		 * by wait_shrink(), and they will be processed from
>> +		 * _pcs_shrink_end().
>> +		 */
> 
> Why do we have to wait already submitted aio reads ?

Because there could be grow requests. This place is broken, I'm fixing that at the moment.
One-dimensional size.op is not enough to drive race between grow and shrink, we need to
convert PCS_SIZE_* into bit fields like it used to be before.

>>   		inode_dio_wait(req->io_inode);
>>   		/*
>>   		 * Writebackcache was flushed already so it is safe to
>>