Messages in this thread | | | From | Chuhong Yuan <> | Date | Fri, 2 Aug 2019 23:10:39 +0800 | Subject | Re: [PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount |
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Willem de Bruijn <willemdebruijn.kernel@gmail.com> 于2019年8月2日周五 下午10:53写道: > > On Fri, Aug 2, 2019 at 10:27 AM Chuhong Yuan <hslester96@gmail.com> wrote: > > > > Willem de Bruijn <willemdebruijn.kernel@gmail.com> 于2019年8月2日周五 下午9:40写道: > > > > > > On Fri, Aug 2, 2019 at 4:36 AM Chuhong Yuan <hslester96@gmail.com> wrote: > > > > > > > > refcount_t is better for reference counters since its > > > > implementation can prevent overflows. > > > > So convert atomic_t ref counters to refcount_t. > > > > > > > > Signed-off-by: Chuhong Yuan <hslester96@gmail.com> > > > > --- > > > > Changes in v2: > > > > - Convert refcount from 0-base to 1-base. > > > > > > This changes the initial value from 0 to 1, but does not change the > > > release condition. So this introduces an accounting bug? > > > > I have noticed this problem and have checked other files which use refcount_t. > > I find although the refcounts are 1-based, they still use > > refcount_dec_and_test() > > to check whether the resource should be released. > > One example is drivers/char/mspec.c. > > Therefore I think this is okay and do not change the release condition. > > Indeed it is fine to use refcount_t with a model where the initial > allocation already accounts for the first reference and thus > initializes with refcount_set(.., 1). > > But it is not correct to just change a previously zero initialization > to one. As now an extra refcount_dec will be needed to release state. > But the rest of the code has not changed, so this extra decrement will > not happen. > > For a correct conversion, see for instance commits > > commit db5bce32fbe19f0c7482fb5a40a33178bbe7b11b > net: prepare (struct ubuf_info)->refcnt conversion > > and > > commit c1d1b437816f0afa99202be3cb650c9d174667bc > net: convert (struct ubuf_info)->refcnt to refcount_t > > The second makes a search-and-replace style API change like your > patches (though also notice the additional required #include). >
Thanks for your examples! I will fix the #include in those no base changed patches.
> But the other patch is needed first to change both the initial > atomic_set *and* at least one atomic_inc, to maintain the same > reference count over the object's lifetime. > > That change requires understanding of the object's lifecycle, so I > suggest only making those changes when aware of that whole data path.
I think I had better focus on the 1-based cases first.
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