Re: [RFC PATCH v2 08/16] fs: add pending file update time flag.

[Christian Brauner <brauner@kernel.org>]

On Tue, May 17, 2022 at 01:28:16PM +0200, Jan Kara wrote:
> On Mon 16-05-22 09:47:10, Stefan Roesch wrote:
> > This introduces an optimization for the update time flag and async
> > buffered writes. While an update of the file modification time is
> > pending and is handled by the workers, concurrent writes do not need
> > to wait for this time update to complete.
> > 
> > Signed-off-by: Stefan Roesch <shr@fb.com>
> > ---
> >  fs/inode.c         | 1 +
> >  include/linux/fs.h | 3 +++
> >  2 files changed, 4 insertions(+)
> > 
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 1d0b02763e98..fd18b2c1b7c4 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -2091,6 +2091,7 @@ static int do_file_update_time(struct inode *inode, struct file *file,
> >  		return 0;
> >  
> >  	ret = inode_update_time(inode, now, sync_mode);
> > +	inode->i_flags &= ~S_PENDING_TIME;
> 
> So what protects this update of inode->i_flags? Usually we use
> inode->i_rwsem for that but not all file_update_time() callers hold it...

I think the confusion might come about because file_modified() mentions
that the caller is expected to hold file's inode_lock()... Another
reason why we should probably add more kernel doc with a "Context:" line
explaining what locks are expected to be held to these helpers.