On Fri, Aug 21, 2020 at 10:47:39AM +0200, Peter Zijlstra wrote:
> Sven reported that commit a21ee6055c30 ("lockdep: Change
> hardirq{s_enabled,_context} to per-cpu variables") caused trouble on
> s390 because their this_cpu_*() primitives disable preemption which
> then lands back tracing.
>
> On the one hand, per-cpu ops should use preempt_*able_notrace() and
> raw_local_irq_*(), on the other hand, we can trivialy use raw_cpu_*()
> ops for this.
>
> Fixes: a21ee6055c30 ("lockdep: Change hardirq{s_enabled,_context} to per-cpu
> variables")
> Reported-by: Sven Schnelle <sv...@linux.ibm.com>
> Reviewed-by: Steven Rostedt (VMware) <rost...@goodmis.org>
> Tested-by: Marco Elver <el...@google.com>
Reviewed-by: Joel Fernandes (Google) <j...@joelfernandes.org>
thanks,
- Joel
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> ---
> include/linux/irqflags.h | 6 +++---
> include/linux/lockdep.h | 18 +++++++++++++-----
> kernel/locking/lockdep.c | 4 ++--
> 3 files changed, 18 insertions(+), 10 deletions(-)
>
> --- a/include/linux/irqflags.h
> +++ b/include/linux/irqflags.h
> @@ -53,13 +53,13 @@ DECLARE_PER_CPU(int, hardirq_context);
> extern void trace_hardirqs_off_finish(void);
> extern void trace_hardirqs_on(void);
> extern void trace_hardirqs_off(void);
> -# define lockdep_hardirq_context() (this_cpu_read(hardirq_context))
> +# define lockdep_hardirq_context() (raw_cpu_read(hardirq_context))
> # define lockdep_softirq_context(p) ((p)->softirq_context)
> # define lockdep_hardirqs_enabled() (this_cpu_read(hardirqs_enabled))
> # define lockdep_softirqs_enabled(p) ((p)->softirqs_enabled)
> # define lockdep_hardirq_enter() \
> do { \
> - if (this_cpu_inc_return(hardirq_context) == 1) \
> + if (__this_cpu_inc_return(hardirq_context) == 1)\
> current->hardirq_threaded = 0; \
> } while (0)
> # define lockdep_hardirq_threaded() \
> @@ -68,7 +68,7 @@ do { \
> } while (0)
> # define lockdep_hardirq_exit() \
> do { \
> - this_cpu_dec(hardirq_context); \
> + __this_cpu_dec(hardirq_context); \
> } while (0)
> # define lockdep_softirq_enter() \
> do { \
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -535,19 +535,27 @@ do {
> \
> DECLARE_PER_CPU(int, hardirqs_enabled);
> DECLARE_PER_CPU(int, hardirq_context);
>
> +/*
> + * The below lockdep_assert_*() macros use raw_cpu_read() to access the above
> + * per-cpu variables. This is required because this_cpu_read() will
> potentially
> + * call into preempt/irq-disable and that obviously isn't right. This is also
> + * correct because when IRQs are enabled, it doesn't matter if we
> accidentally
> + * read the value from our previous CPU.
> + */
> +
> #define lockdep_assert_irqs_enabled()
> \
> do { \
> - WARN_ON_ONCE(debug_locks && !this_cpu_read(hardirqs_enabled)); \
> + WARN_ON_ONCE(debug_locks && !raw_cpu_read(hardirqs_enabled)); \
> } while (0)
>
> #define lockdep_assert_irqs_disabled()
> \
> do { \
> - WARN_ON_ONCE(debug_locks && this_cpu_read(hardirqs_enabled)); \
> + WARN_ON_ONCE(debug_locks && raw_cpu_read(hardirqs_enabled)); \
> } while (0)
>
> #define lockdep_assert_in_irq()
> \
> do { \
> - WARN_ON_ONCE(debug_locks && !this_cpu_read(hardirq_context)); \
> + WARN_ON_ONCE(debug_locks && !raw_cpu_read(hardirq_context)); \
> } while (0)
>
> #define lockdep_assert_preemption_enabled() \
> @@ -555,7 +563,7 @@ do {
> \
> WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT) && \
> debug_locks && \
> (preempt_count() != 0 || \
> - !this_cpu_read(hardirqs_enabled))); \
> + !raw_cpu_read(hardirqs_enabled))); \
> } while (0)
>
> #define lockdep_assert_preemption_disabled() \
> @@ -563,7 +571,7 @@ do {
> \
> WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT) && \
> debug_locks && \
> (preempt_count() == 0 && \
> - this_cpu_read(hardirqs_enabled))); \
> + raw_cpu_read(hardirqs_enabled))); \
> } while (0)
>
> #else
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -3756,7 +3756,7 @@ void noinstr lockdep_hardirqs_on(unsigne
>
> skip_checks:
> /* we'll do an OFF -> ON transition: */
> - this_cpu_write(hardirqs_enabled, 1);
> + __this_cpu_write(hardirqs_enabled, 1);
> trace->hardirq_enable_ip = ip;
> trace->hardirq_enable_event = ++trace->irq_events;
> debug_atomic_inc(hardirqs_on_events);
> @@ -3795,7 +3795,7 @@ void noinstr lockdep_hardirqs_off(unsign
> /*
> * We have done an ON -> OFF transition:
> */
> - this_cpu_write(hardirqs_enabled, 0);
> + __this_cpu_write(hardirqs_enabled, 0);
> trace->hardirq_disable_ip = ip;
> trace->hardirq_disable_event = ++trace->irq_events;
> debug_atomic_inc(hardirqs_off_events);
>
>
