Re: [PATCH] mm: Improve cmtime update on shared writable mmaps

[Ted Ts'o]

On Wed, Nov 02, 2011 at 04:02:00PM +0100, Jan Kara wrote:
>   That's a good question. Locking of i_flags was always kind of unclear to
> me. They are certainly read without any locks and in the couple of places
> where setting can actually race VFS uses i_mutex for serialization which is
> kind of overkill (and unusable from page fault due to locking constraints).
> Probably using atomic bitops for setting i_flags would be needed.

Adding a set of inode_{test,set,clear}_flag() inline functions, and
then converting accesses of i_flags to use them would be a great
cleanup task.  It's been on my mental todo list for a while, but it's
a pretty invasive change.  What we have right now is definitely racy,
though, and we only get away with it because i_flags changes happen
relatively rarely.  Fixing this would be definitely be a Good Thing.

						- Ted
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