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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Josef Bacik <josef@toxicpanda.com>
Cc: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
	Dave Chinner <david@fromorbit.com>,
	David Sterba <dsterba@suse.com>,
	"linux-btrfs @ vger . kernel . org" <linux-btrfs@vger.kernel.org>,
	Filipe Manana <fdmanana@gmail.com>,
	Christoph Hellwig <hch@lst.de>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH] btrfs: don't call btrfs_sync_file from iomap context
Date: Wed, 2 Sep 2020 09:29:44 -0700	[thread overview]
Message-ID: <20200902162944.GH6090@magnolia> (raw)
In-Reply-To: <43272cc6-4d40-caf7-8777-4ef1e1725c97@toxicpanda.com>

On Wed, Sep 02, 2020 at 07:10:08AM -0400, Josef Bacik wrote:
> On 9/2/20 3:12 AM, Johannes Thumshirn wrote:
> > On 02/09/2020 02:22, Josef Bacik wrote:
> > > Instead now we have to rip
> > > it out until we figure out what to do about it.
> > 
> > I don't think we need to rip out the iomap conversion. We can
> > take my fix albeit not pretty, until we have reworked the locking
> > around ->fsync(). Probably with a big fat comment attached to it.
> > 
> 
> We do, because your fix breaks DSYNC for AIO.  You didn't hit this with
> direct io, you hit it with AIO, and the reason you hit it is because you are
> on zram, so your bio's completed before we exited iomap_dio_rw.  So that was
> the last put on the iomap_dio, and thus we ran
> iomap_dio_complete() and deadlocked.  We can't just drop the DSYNC thing for
> AIO because in the normal case where this doesn't happen we need to know
> when the last thing is finished in order to run ->fsync(), we can't just run
> it after submission.  Thanks,

Bleh, Oracle mail (or vger or something) is being slow again...

It occurred to me that we added iomap_dio_ops.submit_io for the benefit
of btrfs.  Could we solve all this for now by adding a ->write_sync
function pointer to iomap_dio_ops that could lead back into a btrfs
function that would flush the necessary bits without itself taking the
inode lock?  And if a ->write_sync is not supplied, then the caller gets
generic_write_sync?

It's kind of a bandaid, but maybe less bad of one than restructuring the
btrfs locking model under time pressure...

--D

> Josef

  reply	other threads:[~2020-09-02 16:30 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200901130644.12655-1-johannes.thumshirn@wdc.com>
2020-09-01 15:11 ` [RFC PATCH] btrfs: don't call btrfs_sync_file from iomap context Josef Bacik
2020-09-01 17:45   ` Darrick J. Wong
2020-09-01 17:55     ` Josef Bacik
2020-09-01 21:46   ` Dave Chinner
2020-09-01 22:19     ` Josef Bacik
2020-09-01 23:58       ` Dave Chinner
2020-09-02  0:22         ` Josef Bacik
2020-09-02  7:12           ` Johannes Thumshirn
2020-09-02 11:10             ` Josef Bacik
2020-09-02 16:29               ` Darrick J. Wong [this message]
2020-09-02 16:47                 ` Josef Bacik
2020-09-02 11:44         ` Matthew Wilcox
2020-09-02 12:20           ` Dave Chinner
2020-09-02 12:42             ` Josef Bacik
2020-09-03  2:28               ` Dave Chinner
2020-09-03  9:49                 ` Filipe Manana
2020-09-03 16:32   ` Christoph Hellwig
2020-09-03 16:46     ` Josef Bacik
2020-09-07  0:04     ` Dave Chinner
2020-09-15 21:48       ` Goldwyn Rodrigues
2020-09-17  3:09         ` Dave Chinner
2020-09-17  5:52           ` Christoph Hellwig
2020-09-17  6:29             ` Dave Chinner
2020-09-17  6:42               ` Christoph Hellwig

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