| Message ID | 20211126180101.27818-4-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| State | Superseded, archived |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 7:02 PM Dmitry Osipenko <digetx@gmail.com> wrote: > > Add atomic/blocking_notifier_has_unique_priority() helpers which return > true if given handler has unique priority. > > Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > --- > include/linux/notifier.h | 5 +++ > kernel/notifier.c | 69 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 74 insertions(+) > > diff --git a/include/linux/notifier.h b/include/linux/notifier.h > index 924c9d7c8e73..2c4036f225e1 100644 > --- a/include/linux/notifier.h > +++ b/include/linux/notifier.h > @@ -175,6 +175,11 @@ int raw_notifier_call_chain_robust(struct raw_notifier_head *nh, > > bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh); > > +bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh, > + struct notifier_block *nb); > +bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh, > + struct notifier_block *nb); > + > #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 b20cb7b9b1f0..7a325b742104 100644 > --- a/kernel/notifier.c > +++ b/kernel/notifier.c > @@ -122,6 +122,19 @@ static int notifier_call_chain_robust(struct notifier_block **nl, > return ret; > } > > +static int notifier_has_unique_priority(struct notifier_block **nl, > + struct notifier_block *n) > +{ > + while (*nl && (*nl)->priority >= n->priority) { > + if ((*nl)->priority == n->priority && *nl != n) > + return false; > + > + nl = &((*nl)->next); > + } > + > + return true; > +} > + > /* > * Atomic notifier chain routines. Registration and unregistration > * use a spinlock, and call_chain is synchronized by RCU (no locks). > @@ -203,6 +216,30 @@ int atomic_notifier_call_chain(struct atomic_notifier_head *nh, > EXPORT_SYMBOL_GPL(atomic_notifier_call_chain); > NOKPROBE_SYMBOL(atomic_notifier_call_chain); > > +/** > + * atomic_notifier_has_unique_priority - Checks whether notifier's priority is unique > + * @nh: Pointer to head of the atomic notifier chain > + * @n: Entry in notifier chain to check > + * > + * Checks whether there is another notifier in the chain with the same priority. > + * Must be called in process context. > + * > + * Returns true if priority is unique, false otherwise. > + */ > +bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh, > + struct notifier_block *n) > +{ > + unsigned long flags; > + bool ret; > + > + spin_lock_irqsave(&nh->lock, flags); > + ret = notifier_has_unique_priority(&nh->head, n); > + spin_unlock_irqrestore(&nh->lock, flags); This only works if the caller can prevent new entries from being added to the list at this point or if the caller knows that they cannot be added for some reason, but the kerneldoc doesn't mention this limitation. > + > + return ret; > +} > +EXPORT_SYMBOL_GPL(atomic_notifier_has_unique_priority); > + > /* > * Blocking notifier chain routines. All access to the chain is > * synchronized by an rwsem. > @@ -336,6 +373,38 @@ bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh) > } > EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty); > > +/** > + * blocking_notifier_has_unique_priority - Checks whether notifier's priority is unique > + * @nh: Pointer to head of the blocking notifier chain > + * @n: Entry in notifier chain to check > + * > + * Checks whether there is another notifier in the chain with the same priority. > + * Must be called in process context. > + * > + * Returns true if priority is unique, false otherwise. > + */ > +bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh, > + struct notifier_block *n) > +{ > + bool ret; > + > + /* > + * This code gets used during boot-up, when task switching is > + * not yet working and interrupts must remain disabled. At such > + * times we must not call down_read(). > + */ > + if (system_state != SYSTEM_BOOTING) No, please don't do this, it makes the whole thing error-prone. > + down_read(&nh->rwsem); > + > + ret = notifier_has_unique_priority(&nh->head, n); > + > + if (system_state != SYSTEM_BOOTING) > + up_read(&nh->rwsem); And still what if a new entry with a non-unique priority is added to the chain at this point? > + > + return ret; > +} > +EXPORT_SYMBOL_GPL(blocking_notifier_has_unique_priority); > + > /* > * Raw notifier chain routines. There is no protection; > * the caller must provide it. Use at your own risk! > -- > 2.33.1 >
10.12.2021 21:19, Rafael J. Wysocki пишет: ... >> +bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh, >> + struct notifier_block *n) >> +{ >> + unsigned long flags; >> + bool ret; >> + >> + spin_lock_irqsave(&nh->lock, flags); >> + ret = notifier_has_unique_priority(&nh->head, n); >> + spin_unlock_irqrestore(&nh->lock, flags); > > This only works if the caller can prevent new entries from being added > to the list at this point or if the caller knows that they cannot be > added for some reason, but the kerneldoc doesn't mention this > limitation. I'll update the comment. .. >> +bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh, >> + struct notifier_block *n) >> +{ >> + bool ret; >> + >> + /* >> + * This code gets used during boot-up, when task switching is >> + * not yet working and interrupts must remain disabled. At such >> + * times we must not call down_read(). >> + */ >> + if (system_state != SYSTEM_BOOTING) > > No, please don't do this, it makes the whole thing error-prone. What should I do then? >> + down_read(&nh->rwsem); >> + >> + ret = notifier_has_unique_priority(&nh->head, n); >> + >> + if (system_state != SYSTEM_BOOTING) >> + up_read(&nh->rwsem); > > And still what if a new entry with a non-unique priority is added to > the chain at this point? If entry with a non-unique priority is added after the check, then obviously it won't be detected. I don't understand the question. These down/up_read() are the locks that prevent the race, if that's the question.
On Fri, Dec 10, 2021 at 7:52 PM Dmitry Osipenko <digetx@gmail.com> wrote: > > 10.12.2021 21:19, Rafael J. Wysocki пишет: > ... > >> +bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh, > >> + struct notifier_block *n) > >> +{ > >> + unsigned long flags; > >> + bool ret; > >> + > >> + spin_lock_irqsave(&nh->lock, flags); > >> + ret = notifier_has_unique_priority(&nh->head, n); > >> + spin_unlock_irqrestore(&nh->lock, flags); > > > > This only works if the caller can prevent new entries from being added > > to the list at this point or if the caller knows that they cannot be > > added for some reason, but the kerneldoc doesn't mention this > > limitation. > > I'll update the comment. > > .. > >> +bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh, > >> + struct notifier_block *n) > >> +{ > >> + bool ret; > >> + > >> + /* > >> + * This code gets used during boot-up, when task switching is > >> + * not yet working and interrupts must remain disabled. At such > >> + * times we must not call down_read(). > >> + */ > >> + if (system_state != SYSTEM_BOOTING) > > > > No, please don't do this, it makes the whole thing error-prone. > > What should I do then? First of all, do you know of any users who may want to call this during early initialization? If so, then why may they want to do that? Depending on the above, I would consider adding a special mechanism for them. > >> + down_read(&nh->rwsem); > >> + > >> + ret = notifier_has_unique_priority(&nh->head, n); > >> + > >> + if (system_state != SYSTEM_BOOTING) > >> + up_read(&nh->rwsem); > > > > And still what if a new entry with a non-unique priority is added to > > the chain at this point? > > If entry with a non-unique priority is added after the check, then > obviously it won't be detected. Why isn't this a problem? > I don't understand the question. These > down/up_read() are the locks that prevent the race, if that's the question. Not really, they only prevent the race from occurring while notifier_has_unique_priority() is running. If anyone depends on this check for correctness, they need to lock the rwsem, do the check, do the thing depending on the check while holding the rwsem and then release the rwsem. Otherwise it is racy.
10.12.2021 22:05, Rafael J. Wysocki пишет: > On Fri, Dec 10, 2021 at 7:52 PM Dmitry Osipenko <digetx@gmail.com> wrote: >> >> 10.12.2021 21:19, Rafael J. Wysocki пишет: >> ... >>>> +bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh, >>>> + struct notifier_block *n) >>>> +{ >>>> + unsigned long flags; >>>> + bool ret; >>>> + >>>> + spin_lock_irqsave(&nh->lock, flags); >>>> + ret = notifier_has_unique_priority(&nh->head, n); >>>> + spin_unlock_irqrestore(&nh->lock, flags); >>> >>> This only works if the caller can prevent new entries from being added >>> to the list at this point or if the caller knows that they cannot be >>> added for some reason, but the kerneldoc doesn't mention this >>> limitation. >> >> I'll update the comment. >> >> .. >>>> +bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh, >>>> + struct notifier_block *n) >>>> +{ >>>> + bool ret; >>>> + >>>> + /* >>>> + * This code gets used during boot-up, when task switching is >>>> + * not yet working and interrupts must remain disabled. At such >>>> + * times we must not call down_read(). >>>> + */ >>>> + if (system_state != SYSTEM_BOOTING) >>> >>> No, please don't do this, it makes the whole thing error-prone. >> >> What should I do then? > > First of all, do you know of any users who may want to call this > during early initialization? If so, then why may they want to do > that? I'll need to carefully review all those dozens of platform restart handlers to answer this question. > Depending on the above, I would consider adding a special mechanism for them. Please notice that every blocking_notifier_*() function has this SYSTEM_BOOTING check, it's not my invention. Notifier API needs to be generic. >>>> + down_read(&nh->rwsem); >>>> + >>>> + ret = notifier_has_unique_priority(&nh->head, n); >>>> + >>>> + if (system_state != SYSTEM_BOOTING) >>>> + up_read(&nh->rwsem); >>> >>> And still what if a new entry with a non-unique priority is added to >>> the chain at this point? >> >> If entry with a non-unique priority is added after the check, then >> obviously it won't be detected. > > Why isn't this a problem?>> I don't understand the question. These >> down/up_read() are the locks that prevent the race, if that's the question. > > Not really, they only prevent the race from occurring while > notifier_has_unique_priority() is running. > > If anyone depends on this check for correctness, they need to lock the > rwsem, do the check, do the thing depending on the check while holding > the rwsem and then release the rwsem. Otherwise it is racy. > It's fine that it's a bit "racy" since in the context of this series. We always do the check after adding new entry, so it's not a problem. There are two options: 1. Use blocking_notifier_has_unique_priority() like it's done in this patchset. Remove it after all drivers are converted to the new API and add blocking_notifier_chain_register_unique(). 2. Add blocking_notifier_chain_register_unique(), but don't let it fail the registration of non-unique entries until all drivers are converted to the new API.
10.12.2021 22:33, Dmitry Osipenko пишет: >> Not really, they only prevent the race from occurring while >> notifier_has_unique_priority() is running. >> >> If anyone depends on this check for correctness, they need to lock the >> rwsem, do the check, do the thing depending on the check while holding >> the rwsem and then release the rwsem. Otherwise it is racy. >> > It's fine that it's a bit "racy" since in the context of this series. We > always do the check after adding new entry, so it's not a problem. > > There are two options: > > 1. Use blocking_notifier_has_unique_priority() like it's done in this > patchset. Remove it after all drivers are converted to the new API and > add blocking_notifier_chain_register_unique(). > > 2. Add blocking_notifier_chain_register_unique(), but don't let it fail > the registration of non-unique entries until all drivers are converted > to the new API. There is third, perhaps the best option: 3. Add blocking_notifier_chain_register_unique() and fall back to blocking_notifier_chain_register() if unique fails, do it until all drivers are converted to the new API.
diff --git a/include/linux/notifier.h b/include/linux/notifier.h index 924c9d7c8e73..2c4036f225e1 100644 --- a/include/linux/notifier.h +++ b/include/linux/notifier.h @@ -175,6 +175,11 @@ int raw_notifier_call_chain_robust(struct raw_notifier_head *nh, bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh); +bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh, + struct notifier_block *nb); +bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh, + struct notifier_block *nb); + #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 b20cb7b9b1f0..7a325b742104 100644 --- a/kernel/notifier.c +++ b/kernel/notifier.c @@ -122,6 +122,19 @@ static int notifier_call_chain_robust(struct notifier_block **nl, return ret; } +static int notifier_has_unique_priority(struct notifier_block **nl, + struct notifier_block *n) +{ + while (*nl && (*nl)->priority >= n->priority) { + if ((*nl)->priority == n->priority && *nl != n) + return false; + + nl = &((*nl)->next); + } + + return true; +} + /* * Atomic notifier chain routines. Registration and unregistration * use a spinlock, and call_chain is synchronized by RCU (no locks). @@ -203,6 +216,30 @@ int atomic_notifier_call_chain(struct atomic_notifier_head *nh, EXPORT_SYMBOL_GPL(atomic_notifier_call_chain); NOKPROBE_SYMBOL(atomic_notifier_call_chain); +/** + * atomic_notifier_has_unique_priority - Checks whether notifier's priority is unique + * @nh: Pointer to head of the atomic notifier chain + * @n: Entry in notifier chain to check + * + * Checks whether there is another notifier in the chain with the same priority. + * Must be called in process context. + * + * Returns true if priority is unique, false otherwise. + */ +bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh, + struct notifier_block *n) +{ + unsigned long flags; + bool ret; + + spin_lock_irqsave(&nh->lock, flags); + ret = notifier_has_unique_priority(&nh->head, n); + spin_unlock_irqrestore(&nh->lock, flags); + + return ret; +} +EXPORT_SYMBOL_GPL(atomic_notifier_has_unique_priority); + /* * Blocking notifier chain routines. All access to the chain is * synchronized by an rwsem. @@ -336,6 +373,38 @@ bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh) } EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty); +/** + * blocking_notifier_has_unique_priority - Checks whether notifier's priority is unique + * @nh: Pointer to head of the blocking notifier chain + * @n: Entry in notifier chain to check + * + * Checks whether there is another notifier in the chain with the same priority. + * Must be called in process context. + * + * Returns true if priority is unique, false otherwise. + */ +bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh, + struct notifier_block *n) +{ + bool ret; + + /* + * This code gets used during boot-up, when task switching is + * not yet working and interrupts must remain disabled. At such + * times we must not call down_read(). + */ + if (system_state != SYSTEM_BOOTING) + down_read(&nh->rwsem); + + ret = notifier_has_unique_priority(&nh->head, n); + + if (system_state != SYSTEM_BOOTING) + up_read(&nh->rwsem); + + return ret; +} +EXPORT_SYMBOL_GPL(blocking_notifier_has_unique_priority); + /* * Raw notifier chain routines. There is no protection; * the caller must provide it. Use at your own risk!
Add atomic/blocking_notifier_has_unique_priority() helpers which return true if given handler has unique priority. Signed-off-by: Dmitry Osipenko <digetx@gmail.com> --- include/linux/notifier.h | 5 +++ kernel/notifier.c | 69 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 74 insertions(+)