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

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Message-ID: <20160123223456.GH6033@dastard>
Date:	Sun, 24 Jan 2016 09:34:56 +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 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?

Cheers,

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