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Date:   Fri, 1 Feb 2019 18:05:42 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Jann Horn <jannh@google.com>
Cc:     Matt Mullins <mmullins@fb.com>,
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Subject: Re: [PATCH 05/18] Add io_uring IO interface
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On Fri, Feb 01, 2019 at 06:23:27PM +0100, Jann Horn wrote:

> > Oh, yuck. Uuuh... can we make "struct files_struct" doubly-refcounted,
> > like "struct mm_struct"? One reference type to keep the contents
> > intact (the reference type you normally use, and the type used by
> > uring when the thread is running), and one reference type to just keep
> > the struct itself existing, but without preserving its contents
> > (reference held consistently by the uring thread)?
> 
> Something like this (completely untested); and then instead of the
> current get_files_struct(), you'd do get_files_struct_weak(), and
> while the thread is running, it protects the files_struct from dying
> with tryget_weak_files_struct() / put_files_struct().
> 
> Al, do you have opinions on this?

Yes, but they are not fit for polite company.  IMO the entire approach
is FUBAR; I'll post more detailed review, but what I'd seen so far is
a veto fodder.