On Sat 29-10-16 13:09:25, Linus Torvalds wrote:

On Sat, Oct 29, 2016 at 12:17 PM, Al Viro [off-list ref] wrote:

quoted

AFAICS, the possibility of dropping the last reference to struct file
before ->write_iter() has returned is fundamentally broken.  I might be
missing something subtle here, but...

Ok, let's add a get_file(); fput(); around that whole iter call sequence.

And that's a separate issue from "we should hold the fs freezer lock
around the whole operation". So I think we need both.

Yup, these are two separate issues. I'm fine with adding get_file(); fput()
around the iter call sequence. Then, when we have struct file available for
the whole time ->write_iter runs, I'd prefer to keep the call to fool
lockdep where original file_end_write() call was - that gives us proper
lockdep coverage for all the code behind iter_op(). The downside is we
cannot keep helpers as elegant as you suggested in your patch but I believe
it's bearable and worth the additional lockdep coverage. I'll send patches
shortly...

								Honza 

-- 
Jan Kara [off-list ref]
SUSE Labs, CR