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

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Date:   Fri, 29 Nov 2019 04:35:15 +0100
From:   Javier Gonzalez <javier@...igon.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Damien Le Moal <damien.lemoal@....com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>,
        linux-fsdevel@...r.kernel.org,
        Shinichiro Kawasaki <shinichiro.kawasaki@....com>
Subject: Re: [PATCH] f2fs: Fix direct IO handling

On 26.11.2019 15:44, Jaegeuk Kim wrote:
>On 11/26, Damien Le Moal wrote:
>> f2fs_preallocate_blocks() identifies direct IOs using the IOCB_DIRECT
>> flag for a kiocb structure. However, the file system direct IO handler
>> function f2fs_direct_IO() may have decided that a direct IO has to be
>> exececuted as a buffered IO using the function f2fs_force_buffered_io().
>> This is the case for instance for volumes including zoned block device
>> and for unaligned write IOs with LFS mode enabled.
>>
>> These 2 different methods of identifying direct IOs can result in
>> inconsistencies generating stale data access for direct reads after a
>> direct IO write that is treated as a buffered write. Fix this
>> inconsistency by combining the IOCB_DIRECT flag test with the result
>> of f2fs_force_buffered_io().
>>
>> Reported-by: Javier Gonzalez <javier@...igon.com>
>> Signed-off-by: Damien Le Moal <damien.lemoal@....com>
>> ---
>>  fs/f2fs/data.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 5755e897a5f0..8ac2d3b70022 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -1073,6 +1073,8 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
>>  	int flag;
>>  	int err = 0;
>>  	bool direct_io = iocb->ki_flags & IOCB_DIRECT;
>> +	bool do_direct_io = direct_io &&
>> +		!f2fs_force_buffered_io(inode, iocb, from);
>>
>>  	/* convert inline data for Direct I/O*/
>>  	if (direct_io) {
>> @@ -1081,7 +1083,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
>>  			return err;
>>  	}
>>
>> -	if (direct_io && allow_outplace_dio(inode, iocb, from))
>> +	if (do_direct_io && allow_outplace_dio(inode, iocb, from))
>
>It seems f2fs_force_buffered_io() includes allow_outplace_dio().
>
>How about this?
>---
> fs/f2fs/data.c | 13 -------------
> fs/f2fs/file.c | 35 +++++++++++++++++++++++++----------
> 2 files changed, 25 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..6b32ac6c3382 100644
>--- a/fs/f2fs/file.c
>+++ b/fs/f2fs/file.c
>@@ -3386,18 +3386,33 @@ 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*/
>+			err = f2fs_convert_inline_inode(inode);
>+			if (err)
>+				goto out_err;
>+
>+			if (!f2fs_force_buffered_io(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
>
This also addresses the original problem.

Tested-by: Javier González <javier@...igon.com>