On Fri, May 03, 2024 at 11:37:25AM +0200, Christian Brauner wrote: > On Thu, May 02, 2024 at 05:41:23PM -0700, Kees Cook wrote: > > On Fri, May 03, 2024 at 01:14:45AM +0100, Al Viro wrote: > > > On Thu, May 02, 2024 at 05:10:18PM -0700, Kees Cook wrote: > > > > > > > But anyway, there needs to be a general "oops I hit 0"-aware form of > > > > get_file(), and it seems like it should just be get_file() itself... > > > > > > ... which brings back the question of what's the sane damage mitigation > > > for that. Adding arseloads of never-exercised failure exits is generally > > > a bad idea - it's asking for bitrot and making the thing harder to review > > > in future. > > > > Linus seems to prefer best-effort error recovery to sprinkling BUG()s > > around. But if that's really the solution, then how about get_file() > > switching to to use inc_not_zero and BUG on 0? > > Making get_file() return an error is not an option. For all current > callers that's pointless churn for a condition that's not supposed to > happen at all. > > Additionally, iirc *_inc_not_zero() variants are implemented with > try_cmpxchg() which scales poorly under contention for a condition > that's not supposed to happen. unsigned long old = atomic_long_fetch_inc_relaxed(&f->f_count); WARN_ON(!old); Or somesuch might be an option?
