| Message ID | 20170802143748.dmthd3hvbq5pbelt@hirez.programming.kicks-ass.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 02/08/17 15:37, Peter Zijlstra wrote: > On Tue, Aug 01, 2017 at 09:02:56AM +0100, Marc Zyngier wrote: >> As using the normal static key API under the hotplug lock is >> pretty much impossible, let's provide a variant of some of them >> that require the hotplug lock to have already been taken. >> >> These function are only meant to be used in CPU hotplug callbacks. >> >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> >> --- >> Documentation/static-keys.txt | 15 +++++++++++++++ >> include/linux/jump_label.h | 11 +++++++++-- >> kernel/jump_label.c | 20 ++++++++++++++++++++ >> 3 files changed, 44 insertions(+), 2 deletions(-) > > I stuffed them in my locking/core branch on top of Paolo's patches: > > https://lkml.kernel.org/r/1501601046-35683-1-git-send-email-pbonzini@redhat.com > > This patch now looks like so. > > --- > Subject: jump_label: Provide hotplug context variants > From: Marc Zyngier <marc.zyngier@arm.com> > Date: Tue, 1 Aug 2017 09:02:56 +0100 > > As using the normal static key API under the hotplug lock is > pretty much impossible, let's provide a variant of some of them > that require the hotplug lock to have already been taken. > > These function are only meant to be used in CPU hotplug callbacks. > > Cc: linux-arm-kernel@lists.infradead.org > Cc: Leo Yan <leo.yan@linaro.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Link: http://lkml.kernel.org/r/20170801080257.5056-4-marc.zyngier@arm.com > --- > Documentation/static-keys.txt | 15 +++++++++++++++ > include/linux/jump_label.h | 11 +++++++++-- > kernel/jump_label.c | 22 ++++++++++++++++++---- > 3 files changed, 42 insertions(+), 6 deletions(-) > > --- a/Documentation/static-keys.txt > +++ b/Documentation/static-keys.txt > @@ -154,6 +154,21 @@ and 'static_key_count()'. In general, i > should be protected with the same mutex used around the enable/disable > or increment/decrement function. > > +Note that switching branches results in some locks being taken, > +particularly the CPU hotplug lock (in order to avoid races against > +CPUs being brought in the kernel whilst the kernel is getting > +patched). Calling the static key API from within a hotplug notifier is > +thus a sure deadlock recipe. In order to still allow use of the > +functionnality, the following functions are provided: > + > + static_key_enable_cpuslocked() > + static_key_disable_cpuslocked() > + static_branch_enable_cpuslocked() > + static_branch_disable_cpuslocked() > + > +These functions are *not* general purpose, and must only be used when > +you really know that you're in the above context, and no other. > + > Where an array of keys is required, it can be defined as:: > > DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count); > --- a/include/linux/jump_label.h > +++ b/include/linux/jump_label.h > @@ -163,6 +163,8 @@ extern void jump_label_apply_nops(struct > extern int static_key_count(struct static_key *key); > extern void static_key_enable(struct static_key *key); > extern void static_key_disable(struct static_key *key); > +extern void static_key_enable_cpuslocked(struct static_key *key); > +extern void static_key_disable_cpuslocked(struct static_key *key); > > /* > * We should be using ATOMIC_INIT() for initializing .enabled, but > @@ -254,6 +256,9 @@ static inline void static_key_disable(st > atomic_set(&key->enabled, 0); > } > > +#define static_key_enable_cpuslocked(k) static_key_enable((k)) > +#define static_key_disable_cpuslocked(k) static_key_disable((k)) > + > #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } > #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } > > @@ -415,8 +420,10 @@ extern bool ____wrong_branch_error(void) > * Normal usage; boolean enable/disable. > */ > > -#define static_branch_enable(x) static_key_enable(&(x)->key) > -#define static_branch_disable(x) static_key_disable(&(x)->key) > +#define static_branch_enable(x) static_key_enable(&(x)->key) > +#define static_branch_disable(x) static_key_disable(&(x)->key) > +#define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) > +#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) > > #endif /* __ASSEMBLY__ */ > > --- a/kernel/jump_label.c > +++ b/kernel/jump_label.c > @@ -126,15 +126,15 @@ void static_key_slow_inc(struct static_k > } > EXPORT_SYMBOL_GPL(static_key_slow_inc); > > -void static_key_enable(struct static_key *key) > +void static_key_enable_cpuslocked(struct static_key *key) > { > STATIC_KEY_CHECK_USE(); > + > if (atomic_read(&key->enabled) > 0) { > WARN_ON_ONCE(atomic_read(&key->enabled) != 1); > return; > } > > - cpus_read_lock(); > jump_label_lock(); > if (atomic_read(&key->enabled) == 0) { > atomic_set(&key->enabled, -1); > @@ -145,23 +145,37 @@ void static_key_enable(struct static_key > atomic_set_release(&key->enabled, 1); > } > jump_label_unlock(); > +} > +EXPORT_SYMBOL_GPL(static_key_enable_cpuslocked); > + > +void static_key_enable(struct static_key *key) > +{ > + cpus_read_lock(); > + static_key_enable_cpuslocked(key); > cpus_read_unlock(); > } > EXPORT_SYMBOL_GPL(static_key_enable); > > -void static_key_disable(struct static_key *key) > +void static_key_disable_cpuslocked(struct static_key *key) > { > STATIC_KEY_CHECK_USE(); > + > if (atomic_read(&key->enabled) != 1) { > WARN_ON_ONCE(atomic_read(&key->enabled) != 0); > return; > } > > - cpus_read_lock(); > jump_label_lock(); > if (atomic_cmpxchg(&key->enabled, 1, 0)) > jump_label_update(key); > jump_label_unlock(); > +} > +EXPORT_SYMBOL_GPL(static_key_disable_cpuslocked); > + > +void static_key_disable(struct static_key *key) > +{ > + cpus_read_lock(); > + static_key_disable_cpuslocked(key); > cpus_read_unlock(); > } > EXPORT_SYMBOL_GPL(static_key_disable); > I've just tried this one of the affected systems, and it booted just fine. So thumbs up from me. Thanks again, M.
--- a/Documentation/static-keys.txt +++ b/Documentation/static-keys.txt @@ -154,6 +154,21 @@ and 'static_key_count()'. In general, i should be protected with the same mutex used around the enable/disable or increment/decrement function. +Note that switching branches results in some locks being taken, +particularly the CPU hotplug lock (in order to avoid races against +CPUs being brought in the kernel whilst the kernel is getting +patched). Calling the static key API from within a hotplug notifier is +thus a sure deadlock recipe. In order to still allow use of the +functionnality, the following functions are provided: + + static_key_enable_cpuslocked() + static_key_disable_cpuslocked() + static_branch_enable_cpuslocked() + static_branch_disable_cpuslocked() + +These functions are *not* general purpose, and must only be used when +you really know that you're in the above context, and no other. + Where an array of keys is required, it can be defined as:: DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count); --- a/include/linux/jump_label.h +++ b/include/linux/jump_label.h @@ -163,6 +163,8 @@ extern void jump_label_apply_nops(struct extern int static_key_count(struct static_key *key); extern void static_key_enable(struct static_key *key); extern void static_key_disable(struct static_key *key); +extern void static_key_enable_cpuslocked(struct static_key *key); +extern void static_key_disable_cpuslocked(struct static_key *key); /* * We should be using ATOMIC_INIT() for initializing .enabled, but @@ -254,6 +256,9 @@ static inline void static_key_disable(st atomic_set(&key->enabled, 0); } +#define static_key_enable_cpuslocked(k) static_key_enable((k)) +#define static_key_disable_cpuslocked(k) static_key_disable((k)) + #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } @@ -415,8 +420,10 @@ extern bool ____wrong_branch_error(void) * Normal usage; boolean enable/disable. */ -#define static_branch_enable(x) static_key_enable(&(x)->key) -#define static_branch_disable(x) static_key_disable(&(x)->key) +#define static_branch_enable(x) static_key_enable(&(x)->key) +#define static_branch_disable(x) static_key_disable(&(x)->key) +#define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) +#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) #endif /* __ASSEMBLY__ */ --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -126,15 +126,15 @@ void static_key_slow_inc(struct static_k } EXPORT_SYMBOL_GPL(static_key_slow_inc); -void static_key_enable(struct static_key *key) +void static_key_enable_cpuslocked(struct static_key *key) { STATIC_KEY_CHECK_USE(); + if (atomic_read(&key->enabled) > 0) { WARN_ON_ONCE(atomic_read(&key->enabled) != 1); return; } - cpus_read_lock(); jump_label_lock(); if (atomic_read(&key->enabled) == 0) { atomic_set(&key->enabled, -1); @@ -145,23 +145,37 @@ void static_key_enable(struct static_key atomic_set_release(&key->enabled, 1); } jump_label_unlock(); +} +EXPORT_SYMBOL_GPL(static_key_enable_cpuslocked); + +void static_key_enable(struct static_key *key) +{ + cpus_read_lock(); + static_key_enable_cpuslocked(key); cpus_read_unlock(); } EXPORT_SYMBOL_GPL(static_key_enable); -void static_key_disable(struct static_key *key) +void static_key_disable_cpuslocked(struct static_key *key) { STATIC_KEY_CHECK_USE(); + if (atomic_read(&key->enabled) != 1) { WARN_ON_ONCE(atomic_read(&key->enabled) != 0); return; } - cpus_read_lock(); jump_label_lock(); if (atomic_cmpxchg(&key->enabled, 1, 0)) jump_label_update(key); jump_label_unlock(); +} +EXPORT_SYMBOL_GPL(static_key_disable_cpuslocked); + +void static_key_disable(struct static_key *key) +{ + cpus_read_lock(); + static_key_disable_cpuslocked(key); cpus_read_unlock(); } EXPORT_SYMBOL_GPL(static_key_disable);