linux-kernel - Re: [git pull] vfs.git - including i

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Date:	Sun, 24 Jan 2016 09:44:35 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [git pull] vfs.git - including i_mutex wrappers

On Sun, Jan 24, 2016 at 09:34:56AM +1100, Dave Chinner wrote:
> On Sat, Jan 23, 2016 at 02:58:54PM +0000, Al Viro wrote:
> > 	->i_mutex wrappers (with small prereq in lustre), fix for too
> 
> Please explain, Al?
> 
> I haven't heard anything about there being i_mutex changes pending,
> and this commit says "over the coming cycle ->i_mutex will become
> rwsem".  That's a complete surprise to me, and not something that
> should be done with no warning.
> 
> What's the locking model? How are filesystems supposed to use it?
> Are they even allowed to use read-mode locking, and if so, what
> operations is it going to be safe to hold the lock in read mode?
> 
> Why is this change considered valid now, when previously there's
> always been significant push-back to any suggestion that we should
> make the i_mutex a rwsem so we can do shared read-only access
> locking on inode operations?

FWIW, I'm not opposed to making such a locking change - I'm more
concerned about the fact I'm finding out about plans for such a
fundamental locking change from a pull request on the last day of a
merge window....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com