On Fri, Aug 2, 2019 at 10:27 AM Chuhong Yuan <[email protected]> wrote: > > Willem de Bruijn <[email protected]> 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 <[email protected]> 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 <[email protected]> > > > --- > > > 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). 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.
