| Message ID | 20211126180101.27818-3-digetx@gmail.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | Introduce power-off+restart call chain API | expand |
On Fri, Nov 26, 2021 at 7:01 PM Dmitry Osipenko <digetx@gmail.com> wrote: > > Add blocking_notifier_call_chain_is_empty() that returns true if call > chain is empty. > > Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > --- > include/linux/notifier.h | 2 ++ > kernel/notifier.c | 14 ++++++++++++++ > 2 files changed, 16 insertions(+) > > diff --git a/include/linux/notifier.h b/include/linux/notifier.h > index 4b80a815b666..924c9d7c8e73 100644 > --- a/include/linux/notifier.h > +++ b/include/linux/notifier.h > @@ -173,6 +173,8 @@ int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh, > int raw_notifier_call_chain_robust(struct raw_notifier_head *nh, > unsigned long val_up, unsigned long val_down, void *v); > > +bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh); > + > #define NOTIFY_DONE 0x0000 /* Don't care */ > #define NOTIFY_OK 0x0001 /* Suits me */ > #define NOTIFY_STOP_MASK 0x8000 /* Don't call further */ > diff --git a/kernel/notifier.c b/kernel/notifier.c > index b8251dc0bc0f..b20cb7b9b1f0 100644 > --- a/kernel/notifier.c > +++ b/kernel/notifier.c > @@ -322,6 +322,20 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh, > } > EXPORT_SYMBOL_GPL(blocking_notifier_call_chain); > > +/** > + * blocking_notifier_call_chain_is_empty - Check whether notifier chain is empty > + * @nh: Pointer to head of the blocking notifier chain > + * > + * Checks whether notifier chain is empty. > + * > + * Returns true is notifier chain is empty, false otherwise. > + */ > +bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh) > +{ > + return !rcu_access_pointer(nh->head); > +} > +EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty); The check is not reliable (racy) without locking, so I wouldn't export anything like this to modules. At least IMO it should be added along with a user.
10.12.2021 21:14, Rafael J. Wysocki пишет: > On Fri, Nov 26, 2021 at 7:01 PM Dmitry Osipenko <digetx@gmail.com> wrote: >> >> Add blocking_notifier_call_chain_is_empty() that returns true if call >> chain is empty. >> >> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> >> --- >> include/linux/notifier.h | 2 ++ >> kernel/notifier.c | 14 ++++++++++++++ >> 2 files changed, 16 insertions(+) >> >> diff --git a/include/linux/notifier.h b/include/linux/notifier.h >> index 4b80a815b666..924c9d7c8e73 100644 >> --- a/include/linux/notifier.h >> +++ b/include/linux/notifier.h >> @@ -173,6 +173,8 @@ int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh, >> int raw_notifier_call_chain_robust(struct raw_notifier_head *nh, >> unsigned long val_up, unsigned long val_down, void *v); >> >> +bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh); >> + >> #define NOTIFY_DONE 0x0000 /* Don't care */ >> #define NOTIFY_OK 0x0001 /* Suits me */ >> #define NOTIFY_STOP_MASK 0x8000 /* Don't call further */ >> diff --git a/kernel/notifier.c b/kernel/notifier.c >> index b8251dc0bc0f..b20cb7b9b1f0 100644 >> --- a/kernel/notifier.c >> +++ b/kernel/notifier.c >> @@ -322,6 +322,20 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh, >> } >> EXPORT_SYMBOL_GPL(blocking_notifier_call_chain); >> >> +/** >> + * blocking_notifier_call_chain_is_empty - Check whether notifier chain is empty >> + * @nh: Pointer to head of the blocking notifier chain >> + * >> + * Checks whether notifier chain is empty. >> + * >> + * Returns true is notifier chain is empty, false otherwise. >> + */ >> +bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh) >> +{ >> + return !rcu_access_pointer(nh->head); >> +} >> +EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty); > > The check is not reliable (racy) without locking, so I wouldn't export > anything like this to modules. > > At least IMO it should be added along with a user. > I'll remove the export since it's indeed not obvious how other users may want to use this function.
diff --git a/include/linux/notifier.h b/include/linux/notifier.h index 4b80a815b666..924c9d7c8e73 100644 --- a/include/linux/notifier.h +++ b/include/linux/notifier.h @@ -173,6 +173,8 @@ int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh, int raw_notifier_call_chain_robust(struct raw_notifier_head *nh, unsigned long val_up, unsigned long val_down, void *v); +bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh); + #define NOTIFY_DONE 0x0000 /* Don't care */ #define NOTIFY_OK 0x0001 /* Suits me */ #define NOTIFY_STOP_MASK 0x8000 /* Don't call further */ diff --git a/kernel/notifier.c b/kernel/notifier.c index b8251dc0bc0f..b20cb7b9b1f0 100644 --- a/kernel/notifier.c +++ b/kernel/notifier.c @@ -322,6 +322,20 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh, } EXPORT_SYMBOL_GPL(blocking_notifier_call_chain); +/** + * blocking_notifier_call_chain_is_empty - Check whether notifier chain is empty + * @nh: Pointer to head of the blocking notifier chain + * + * Checks whether notifier chain is empty. + * + * Returns true is notifier chain is empty, false otherwise. + */ +bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh) +{ + return !rcu_access_pointer(nh->head); +} +EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty); + /* * Raw notifier chain routines. There is no protection; * the caller must provide it. Use at your own risk!
Add blocking_notifier_call_chain_is_empty() that returns true if call chain is empty. Signed-off-by: Dmitry Osipenko <digetx@gmail.com> --- include/linux/notifier.h | 2 ++ kernel/notifier.c | 14 ++++++++++++++ 2 files changed, 16 insertions(+)