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From: Stefan Roesch <[email protected]>
To: Dave Chinner <[email protected]>
Cc: [email protected], [email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [RFC PATCH v1 11/18] xfs: add async buffered write support
Date: Mon, 9 May 2022 12:32:59 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>



On 5/6/22 2:29 AM, Dave Chinner wrote:
> On Mon, May 02, 2022 at 02:21:17PM -0700, Stefan Roesch wrote:
>>
>>
>> On 4/28/22 2:54 PM, Dave Chinner wrote:
>>> On Thu, Apr 28, 2022 at 12:58:59PM -0700, Stefan Roesch wrote:
>>>>
>>>>
>>>> On 4/26/22 3:56 PM, Dave Chinner wrote:
>>>>> On Tue, Apr 26, 2022 at 10:43:28AM -0700, Stefan Roesch wrote:
>>>>>> This adds the async buffered write support to XFS. For async buffered
>>>>>> write requests, the request will return -EAGAIN if the ilock cannot be
>>>>>> obtained immediately.
>>>>>>
>>>>>> Signed-off-by: Stefan Roesch <[email protected]>
>>>>>> ---
>>>>>>  fs/xfs/xfs_file.c | 10 ++++++----
>>>>>>  1 file changed, 6 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
>>>>>> index 6f9da1059e8b..49d54b939502 100644
>>>>>> --- a/fs/xfs/xfs_file.c
>>>>>> +++ b/fs/xfs/xfs_file.c
>>>>>> @@ -739,12 +739,14 @@ xfs_file_buffered_write(
>>>>>>  	bool			cleared_space = false;
>>>>>>  	int			iolock;
>>>>>>  
>>>>>> -	if (iocb->ki_flags & IOCB_NOWAIT)
>>>>>> -		return -EOPNOTSUPP;
>>>>>> -
>>>>>>  write_retry:
>>>>>>  	iolock = XFS_IOLOCK_EXCL;
>>>>>> -	xfs_ilock(ip, iolock);
>>>>>> +	if (iocb->ki_flags & IOCB_NOWAIT) {
>>>>>> +		if (!xfs_ilock_nowait(ip, iolock))
>>>>>> +			return -EAGAIN;
>>>>>> +	} else {
>>>>>> +		xfs_ilock(ip, iolock);
>>>>>> +	}
>>>>>
>>>>> xfs_ilock_iocb().
>>>>>
>>>>
>>>> The helper xfs_ilock_iocb cannot be used as it hardcoded to use iocb->ki_filp to
>>>> get a pointer to the xfs_inode.
>>>
>>> And the problem with that is?
>>>
>>> I mean, look at what xfs_file_buffered_write() does to get the
>>> xfs_inode 10 lines about that change:
>>>
>>> xfs_file_buffered_write(
>>>         struct kiocb            *iocb,
>>>         struct iov_iter         *from)
>>> {
>>>         struct file             *file = iocb->ki_filp;
>>>         struct address_space    *mapping = file->f_mapping;
>>>         struct inode            *inode = mapping->host;
>>>         struct xfs_inode        *ip = XFS_I(inode);
>>>
>>> In what cases does file_inode(iocb->ki_filp) point to a different
>>> inode than iocb->ki_filp->f_mapping->host? The dio write path assumes
>>> that file_inode(iocb->ki_filp) is correct, as do both the buffered
>>> and dio read paths.
>>>
>>> What makes the buffered write path special in that
>>> file_inode(iocb->ki_filp) is not correctly set whilst
>>> iocb->ki_filp->f_mapping->host is?
>>>
>>
>> In the function xfs_file_buffered_write() the code calls the function 
>> xfs_ilock(). The xfs_inode pointer that is passed in is iocb->ki_filp->f_mapping->host.
>> The one used in xfs_ilock_iocb is ki_filp->f_inode.
>>
>> After getting the lock, the code in xfs_file_buffered_write calls the
>> function xfs_buffered_write_iomap_begin(). In this function the code
>> calls xfs_ilock() for ki_filp->f_inode in exclusive mode.
>>
>> If I replace the first xfs_ilock() call with xfs_ilock_iocb(), then it looks
>> like I get a deadlock.
>>
>> Am I missing something?
> 
> Yes. They take different locks. xfs_file_buffered_write() takes the
> IOLOCK, xfs_buffered_write_iomap_begin() takes the ILOCK....
> 

Thanks for the clarification.

>> I can:
>> - replace the pointer to iocb with pointer to xfs_inode in the function xfs_ilock_iocb()
>>   and also pass in the flags value as a parameter.
>> or
>> - create function xfs_ilock_inode(), which xfs_ilock_iocb() calls. The existing
>>   calls will not need to change, only the xfs_ilock in xfs_file_buffered_write()
>>   will use xfs_ilock_inode().
> 
> You're making this way more complex than it needs to be. As I said:
> 
>>> Regardless, if this is a problem, then just pass the XFS inode to
>>> xfs_ilock_iocb() and this is a moot point.
> 

The function xfs_ilock_iocb() is expecting a pointer to the data structure kiocb, not
a pointer to xfs_inode. I don't see how that's possible without changing the signature
of xfs_ilock_iocb().

Do you want to invoke xfs_ilock_nowait() directly()?


> Cheers,
> 
> Dave.

  reply	other threads:[~2022-05-09 19:33 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-26 17:43 [RFC PATCH v1 00/18] io-uring/xfs: support async buffered writes Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 01/18] block: add check for async buffered writes to generic_write_checks Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 02/18] mm: add FGP_ATOMIC flag to __filemap_get_folio() Stefan Roesch
2022-04-26 19:06   ` Matthew Wilcox
2022-04-28 19:54     ` Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 03/18] iomap: add iomap_page_create_gfp to allocate iomap_pages Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 04/18] iomap: use iomap_page_create_gfp() in __iomap_write_begin Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 05/18] iomap: add async buffered write support Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 06/18] xfs: add iomap " Stefan Roesch
2022-04-26 22:54   ` Dave Chinner
2022-04-28 20:03     ` Stefan Roesch
2022-04-28 21:44       ` Dave Chinner
2022-04-26 17:43 ` [RFC PATCH v1 07/18] fs: split off need_remove_file_privs() do_remove_file_privs() Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 08/18] fs: split off need_file_update_time and do_file_update_time Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 09/18] fs: add pending file update time flag Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 10/18] xfs: Enable async write file modification handling Stefan Roesch
2022-04-26 22:55   ` Dave Chinner
2022-04-27 12:07   ` Christian Brauner
2022-04-26 17:43 ` [RFC PATCH v1 11/18] xfs: add async buffered write support Stefan Roesch
2022-04-26 22:56   ` Dave Chinner
2022-04-28 19:58     ` Stefan Roesch
2022-04-28 21:54       ` Dave Chinner
2022-05-02 21:21         ` Stefan Roesch
2022-05-06  9:29           ` Dave Chinner
2022-05-09 19:32             ` Stefan Roesch [this message]
2022-05-09 23:24               ` Dave Chinner
2022-05-09 23:44                 ` Darrick J. Wong
2022-05-10  1:12                   ` Dave Chinner
2022-05-10  6:47                     ` Christoph Hellwig
2022-05-16  2:24                       ` Dave Chinner
2022-05-16 13:39                         ` Christoph Hellwig
2022-04-26 17:43 ` [RFC PATCH v1 12/18] io_uring: add support for async buffered writes Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 13/18] io_uring: add tracepoint for short writes Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 14/18] sched: add new fields to task_struct Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 15/18] mm: support write throttling for async buffered writes Stefan Roesch
2022-04-28 17:47   ` Jan Kara
2022-04-28 20:16     ` Stefan Roesch
2022-05-10  9:50       ` Jan Kara
2022-05-10 20:16         ` Stefan Roesch
2022-05-11 10:38           ` Jan Kara
2022-05-13 18:57             ` Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 16/18] iomap: User " Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 17/18] io_uring: support write " Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 18/18] xfs: enable async buffered write support Stefan Roesch
2022-04-26 22:37 ` [RFC PATCH v1 00/18] io-uring/xfs: support async buffered writes Dave Chinner

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