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Date:   Tue, 15 Sep 2020 16:48:53 -0500
From:   Goldwyn Rodrigues <rgoldwyn@suse.com>
To:     Dave Chinner <david@fromorbit.com>
Cc:     Christoph Hellwig <hch@lst.de>, Josef Bacik <josef@toxicpanda.com>,
        Johannes Thumshirn <johannes.thumshirn@wdc.com>,
        David Sterba <dsterba@suse.com>,
        "linux-btrfs @ vger . kernel . org" <linux-btrfs@vger.kernel.org>,
        Filipe Manana <fdmanana@gmail.com>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH] btrfs: don't call btrfs_sync_file from iomap context
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On 10:04 07/09, Dave Chinner wrote:
> On Thu, Sep 03, 2020 at 06:32:36PM +0200, Christoph Hellwig wrote:
> > We could trivially do something like this to allow the file system
> > to call iomap_dio_complete without i_rwsem:
> 
> That just exposes another deadlock vector:
> 
> 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>

Can inode_dio_end() be called before generic_write_sync(), as it is done
in fs/direct-io.c:dio_complete()?

Christoph's solution is a clean approach and would prefer to use it as
the final solution.


-- 
Goldwyn