linux-kernel - Re: frequent softlockups with 3.10rc6.

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Message-ID: <20130628082213.GE4165@ZenIV.linux.org.uk>
Date:	Fri, 28 Jun 2013 09:22:13 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Dave Jones <davej@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: frequent softlockups with 3.10rc6.

On Thu, Jun 27, 2013 at 07:59:50PM -1000, Linus Torvalds wrote:

> Also, looking some more now at that wait_sb_inodes logic, I have to
> say that if the problem is primarily the inode->i_lock, then that's
> just crazy.


Looks more like contention on inode_sb_list_lock, actually...

> And no, I don't think really need the i_lock for checking
> "mapping->nrpages == 0" or the magical "inode is being freed" bits
> either. Or at least we could easily do some of this optimistically for
> the common cases.

> I'm attaching a pretty trivial patch, which may obviously be trivially
> totally flawed. I have not tested this in any way, but half the new
> lines are comments about why it's doing what it is doing.  And I
> really think that it should make the "actually take the inode lock" be
> something quite rare.
> 
> And quite frankly, I'd much rather get *rid* of crazy i_lock accesses,
> than try to be clever and use a whole different list at this point.
> Not that I disagree that it wouldn't be much nicer to use a separate
> list in the long run, but for a short-term solution I'd much rather
> keep the old logic and just tweak it to be much more usable..
> 
> Hmm? Al? Jan? Comments?

Patch seems to be sane, but I'm not sure how much will it buy in that
case.
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