linux-kernel - Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish

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Message-ID: <20150912021529.GD4150@ret.masoncoding.com>
Date:	Fri, 11 Sep 2015 22:15:29 -0400
From:	Chris Mason <clm@...com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Josef Bacik <jbacik@...com>, LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug()

On Fri, Sep 11, 2015 at 05:52:27PM -0700, Linus Torvalds wrote:
> On Fri, Sep 11, 2015 at 4:36 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > Are we really ok with waiting synchronously for an inode while holding
> > the plug? No chance of deadlock (waiting for IO that we've plugged)?
> > That issue is true even of the current code, though, and I have _not_
> > really thought that through, it's just a worry.
> 
> Never mind. We still flush the plug on explicit scheduling events.  I
> wonder why I thought we got rid of that. Some kind of "senior moment",

But flushing on schedule is a little different.  It ends up calling
blk_schedule_flush_plug() which will hand off work to kblockd through
blk_run_queue_async()

Not a huge deal, but if we're scheduling to wait for that IO, we should
really run the plug ourselves so that we're not waiting for kblockd too.

-chris
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