linux-kernel - Re: [PATCH v2] f2fs: Fix direct IO handling

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Date:   Wed, 4 Dec 2019 04:01:20 +0000
From:   Shinichiro Kawasaki <shinichiro.kawasaki@....com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     Damien Le Moal <Damien.LeMoal@....com>,
        "linux-f2fs-devel@...ts.sourceforge.net" 
        <linux-f2fs-devel@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chao Yu <yuchao0@...wei.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Javier Gonzalez <javier@...igon.com>
Subject: Re: [PATCH v2] f2fs: Fix direct IO handling

On Dec 03, 2019 / 09:33, Jaegeuk Kim wrote:
> Thank you for checking the patch.
> I found some regressions in xfstests, so want to follow the Damien's one
> like below.
> 
> Thanks,
> 
> ===
> From 9df6f09e3a09ed804aba4b56ff7cd9524c002e69 Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@...nel.org>
> Date: Tue, 26 Nov 2019 15:01:42 -0800
> Subject: [PATCH] f2fs: preallocate DIO blocks when forcing buffered_io
> 
> The previous preallocation and DIO decision like below.
> 
>                          allow_outplace_dio              !allow_outplace_dio
> f2fs_force_buffered_io   (*) No_Prealloc / Buffered_IO   Prealloc / Buffered_IO
> !f2fs_force_buffered_io  No_Prealloc / DIO               Prealloc / DIO
> 
> But, Javier reported Case (*) where zoned device bypassed preallocation but
> fell back to buffered writes in f2fs_direct_IO(), resulting in stale data
> being read.
> 
> In order to fix the issue, actually we need to preallocate blocks whenever
> we fall back to buffered IO like this. No change is made in the other cases.
> 
>                          allow_outplace_dio              !allow_outplace_dio
> f2fs_force_buffered_io   (*) Prealloc / Buffered_IO      Prealloc / Buffered_IO
> !f2fs_force_buffered_io  No_Prealloc / DIO               Prealloc / DIO
> 
> Reported-and-tested-by: Javier Gonzalez <javier@...igon.com>
> Signed-off-by: Damien Le Moal <damien.lemoal@....com>
> Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>

Using SMR disks, I reconfirmed that the reported problem goes away with this
modified patch also. Thanks.

> ---
>  fs/f2fs/data.c | 13 -------------
>  fs/f2fs/file.c | 43 +++++++++++++++++++++++++++++++++----------
>  2 files changed, 33 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index a034cd0ce021..fc40a72f7827 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1180,19 +1180,6 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
>  	int err = 0;
>  	bool direct_io = iocb->ki_flags & IOCB_DIRECT;
>  
> -	/* convert inline data for Direct I/O*/
> -	if (direct_io) {
> -		err = f2fs_convert_inline_inode(inode);
> -		if (err)
> -			return err;
> -	}
> -
> -	if (direct_io && allow_outplace_dio(inode, iocb, from))
> -		return 0;
> -
> -	if (is_inode_flag_set(inode, FI_NO_PREALLOC))
> -		return 0;
> -
>  	map.m_lblk = F2FS_BLK_ALIGN(iocb->ki_pos);
>  	map.m_len = F2FS_BYTES_TO_BLK(iocb->ki_pos + iov_iter_count(from));
>  	if (map.m_len > map.m_lblk)
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index c0560d62dbee..0e1b12a4a4d6 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -3386,18 +3386,41 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  				ret = -EAGAIN;
>  				goto out;
>  			}
> -		} else {
> -			preallocated = true;
> -			target_size = iocb->ki_pos + iov_iter_count(from);
> +			goto write;
> +		}
>  
> -			err = f2fs_preallocate_blocks(iocb, from);
> -			if (err) {
> -				clear_inode_flag(inode, FI_NO_PREALLOC);
> -				inode_unlock(inode);
> -				ret = err;
> -				goto out;
> -			}
> +		if (is_inode_flag_set(inode, FI_NO_PREALLOC))
> +			goto write;
> +
> +		if (iocb->ki_flags & IOCB_DIRECT) {
> +			/*
> +			 * Convert inline data for Direct I/O before entering
> +			 * f2fs_direct_IO().
> +			 */
> +			err = f2fs_convert_inline_inode(inode);
> +			if (err)
> +				goto out_err;
> +			/*
> +			 * If force_buffere_io() is true, we have to allocate
> +			 * blocks all the time, since f2fs_direct_IO will fall
> +			 * back to buffered IO.
> +			 */
> +			if (!f2fs_force_buffered_io(inode, iocb, from) &&
> +					allow_outplace_dio(inode, iocb, from))
> +				goto write;
> +		}
> +		preallocated = true;
> +		target_size = iocb->ki_pos + iov_iter_count(from);
> +
> +		err = f2fs_preallocate_blocks(iocb, from);
> +		if (err) {
> +out_err:
> +			clear_inode_flag(inode, FI_NO_PREALLOC);
> +			inode_unlock(inode);
> +			ret = err;
> +			goto out;
>  		}
> +write:
>  		ret = __generic_file_write_iter(iocb, from);
>  		clear_inode_flag(inode, FI_NO_PREALLOC);
>  
> -- 
> 2.19.0.605.g01d371f741-goog
> 
> 

--
Best Regards,
Shin'ichiro Kawasaki