10.08.2020 03:59, Michał Mirosław пишет: > On Mon, Aug 10, 2020 at 03:21:47AM +0300, Dmitry Osipenko wrote: >> 10.08.2020 01:30, Michał Mirosław пишет: >>> On Mon, Aug 10, 2020 at 12:40:04AM +0300, Dmitry Osipenko wrote: >>>> 10.08.2020 00:16, Michał Mirosław пишет: >>>>> Simplify regulator locking by removing locking around locking. rdev->ref >>>>> is now accessed only when the lock is taken. The code still smells fishy, >>>>> but now its obvious why. >>>>> >>>>> Fixes: f8702f9e4aa7 ("regulator: core: Use ww_mutex for regulators >>>>> locking") >>>>> Signed-off-by: Michał Mirosław <mirq-li...@rere.qmqm.pl> >>>>> --- >>>>> drivers/regulator/core.c | 37 ++++++-------------------------- >>>>> include/linux/regulator/driver.h | 1 - >>>>> 2 files changed, 6 insertions(+), 32 deletions(-) >>>>> >>>>> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c >>>>> index 9e18997777d3..b0662927487c 100644 >>>>> --- a/drivers/regulator/core.c >>>>> +++ b/drivers/regulator/core.c >>>>> @@ -45,7 +45,6 @@ >>>>> pr_debug("%s: " fmt, rdev_get_name(rdev), ##__VA_ARGS__) >>>>> >>>>> static DEFINE_WW_CLASS(regulator_ww_class); >>>>> -static DEFINE_MUTEX(regulator_nesting_mutex); >>>>> static DEFINE_MUTEX(regulator_list_mutex); >>>>> static LIST_HEAD(regulator_map_list); >>>>> static LIST_HEAD(regulator_ena_gpio_list); >>>>> @@ -150,32 +149,13 @@ static bool regulator_ops_is_valid(struct >>>>> regulator_dev *rdev, int ops) >>>>> static inline int regulator_lock_nested(struct regulator_dev *rdev, >>>>> struct ww_acquire_ctx *ww_ctx) >>>>> { >>>>> - bool lock = false; >>>>> int ret = 0; >>>>> >>>>> - mutex_lock(®ulator_nesting_mutex); >>>>> + if (ww_ctx || !mutex_trylock_recursive(&rdev->mutex.base)) >>>> >>>> Have you seen comment to the mutex_trylock_recursive()? >>>> >>>> https://elixir.bootlin.com/linux/v5.8/source/include/linux/mutex.h#L205 >>>> >>>> * This function should not be used, _ever_. It is purely for hysterical >>>> GEM >>>> * raisins, and once those are gone this will be removed. >>>> >>>> I knew about this function and I don't think it's okay to use it, hence >>>> this is why there is that "nesting_mutex" and "owner" checking. >>>> >>>> If you disagree, then perhaps you should make another patch to remove >>>> the stale comment to trylock_recursive(). >>> >>> I think that reimplementing the function just to not use it is not the >>> right solution. The whole locking protocol is problematic and this patch >>> just uncovers one side of it. >> >> It's not clear to me what is uncovered, the ref_cnt was always accessed >> under lock. Could you please explain in a more details? >> >> Would be awesome if you could improve the code, but then you should >> un-deprecate the trylock_recursive() before making use of it. Maybe >> nobody will mind and it all will be good in the end. > > I'm not sure why the framework wants recursive locking? If only for the > coupling case, then ww_mutex seems the right direction to replace it: > while walking the graph it will detect entering the same node > a second time. But this works only during the locking transaction (with > ww_context != NULL). Allowing recursive regulator_lock() outside of it > seems inviting trouble.
Yes, it's for the coupling case. Coupled regulators may have common ancestors and then the whole sub-tree needs to be locked while operating with a coupled regulator. The nested locking usage is discouraged in general because it is a source of bugs. I guess it should be possible to get rid of all nested lockings in the regulator core and use a pure ww_mutex, but somebody should dedicate time to work on it.