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Date:   Tue, 22 Sep 2020 15:21:26 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc:     linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org,
        david@fromorbit.com, hch@lst.de, johannes.thumshirn@wdc.com,
        dsterba@suse.com, darrick.wong@oracle.com, josef@toxicpanda.com,
        Goldwyn Rodrigues <rgoldwyn@suse.com>
Subject: Re: [PATCH 04/15] iomap: Call inode_dio_end() before
 generic_write_sync()
Message-ID: <20200922132126.GC20432@lst.de>
References: <20200921144353.31319-1-rgoldwyn@suse.de> <20200921144353.31319-5-rgoldwyn@suse.de>
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On Mon, Sep 21, 2020 at 09:43:42AM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> iomap complete routine can deadlock with btrfs_fallocate because of the
> call to generic_write_sync().
> 
> P0                      P1
> inode_lock()            fallocate(FALLOC_FL_ZERO_RANGE)
> __iomap_dio_rw()        inode_lock()
>                         <block>
> <submits IO>
> <completes IO>
> inode_unlock()
>                         <gets inode_lock()>
>                         inode_dio_wait()
> iomap_dio_complete()
>   generic_write_sync()
>     btrfs_file_fsync()
>       inode_lock()
>       <deadlock>
> 
> inode_dio_end() is used to notify the end of DIO data in order
> to synchronize with truncate. Call inode_dio_end() before calling
> generic_write_sync(), so filesystems can lock i_rwsem during a sync.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

You might want to mention in the commit log that this matches the
sequence in the old fs/direct-io.c implementation.