On Sun, Sep 27, 2020 at 07:35:26PM -0400, Joel Fernandes wrote: > On Fri, Sep 25, 2020 at 05:47:14PM -0600, Shuah Khan wrote: > > This patch series is a result of discussion at the refcount_t BOF > > the Linux Plumbers Conference. In this discussion, we identified > > a need for looking closely and investigating atomic_t usages in > > the kernel when it is used strictly as a counter without it > > controlling object lifetimes and state changes. > > > > There are a number of atomic_t usages in the kernel where atomic_t api > > is used strictly for counting and not for managing object lifetime. In > > some cases, atomic_t might not even be needed. > > > > The purpose of these counters is twofold: 1. clearly differentiate > > atomic_t counters from atomic_t usages that guard object lifetimes, > > hence prone to overflow and underflow errors. It allows tools that scan > > for underflow and overflow on atomic_t usages to detect overflow and > > underflows to scan just the cases that are prone to errors. 2. provides > > non-atomic counters for cases where atomic isn't necessary. > > Nice series :) > > It appears there is no user of counter_simple in this series other than the > selftest. Would you be planning to add any conversions in the series itself, > for illustration of use? Sorry if I missed a usage. > > Also how do we guard against atomicity of counter_simple RMW operations? Is > the implication that it should be guarded using other synchronization to > prevent lost-update problem? > > Some more comments: > > 1. atomic RMW operations that have a return value are fully ordered. Would > you be adding support to counter_simple for such ordering as well, for > consistency?
No -- there is no atomicity guarantee for counter_simple. I would prefer counter_simple not exist at all, specifically for this reason. > 2. I felt counter_atomic and counter_atomic64 would be nice equivalents to > the atomic and atomic64 naming currently used (i.e. dropping the '32'). > However that is just my opinion and I am ok with either naming. I had asked that they be size-named to avoid any confusion (i.e. we're making a new API). -- Kees Cook
