Re: [PATCH 6.6.y] btrfs: always fallback to buffered write if the inode requires checksum

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 968f19c5b1b7d5595423b0ac0020cc18dfed8cb5

Status in newer kernel trees:
6.14.y | Not found
6.12.y | Not found

Note: The patch differs from the upstream commit:
---
1:  968f19c5b1b7d ! 1:  cf0081b3a1276 btrfs: always fallback to buffered write if the inode requires checksum
    @@ Metadata
      ## Commit message ##
         btrfs: always fallback to buffered write if the inode requires checksum
     
    +    commit 968f19c5b1b7d5595423b0ac0020cc18dfed8cb5 upstream.
    +
         [BUG]
         It is a long known bug that VM image on btrfs can lead to data csum
         mismatch, if the qemu is using direct-io for the image (this is commonly
    @@ Commit message
           to buffered IO.  At least by this, we avoid the more deadly false data
           checksum mismatch error.
     
    +    CC: stable@vger.kernel.org # 6.6
         Suggested-by: Christoph Hellwig <hch@infradead.org>
         Reviewed-by: Filipe Manana <fdmanana@suse.com>
         Signed-off-by: Qu Wenruo <wqu@suse.com>
         Reviewed-by: David Sterba <dsterba@suse.com>
         Signed-off-by: David Sterba <dsterba@suse.com>
    +    [ Fix a conflict due to the movement of the function. ]
     
    - ## fs/btrfs/direct-io.c ##
    -@@ fs/btrfs/direct-io.c: ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
    - 		btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
    + ## fs/btrfs/file.c ##
    +@@ fs/btrfs/file.c: static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
      		goto buffered;
      	}
    + 
     +	/*
     +	 * We can't control the folios being passed in, applications can write
     +	 * to them while a direct IO write is in progress.  This means the
    @@ fs/btrfs/direct-io.c: ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_
     +		btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
     +		goto buffered;
     +	}
    - 
    ++
      	/*
      	 * The iov_iter can be mapped to the same file range we are writing to.
    + 	 * If that's the case, then we will deadlock in the iomap code, because
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.6.y        |  Success    |  Success   |