Messages in this thread | | | Subject | Re: [patch part-II V2 09/13] x86/entry/common: Split hardirq tracing into lockdep and ftrace parts | From | Alexandre Chartre <> | Date | Tue, 10 Mar 2020 14:28:23 +0100 |
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On 3/8/20 11:24 PM, Thomas Gleixner wrote: > trace_hardirqs_off() is in fact a tracepoint which can be utilized by BPF, > which is unsafe before calling enter_from_user_mode(), which in turn > invokes context tracking. trace_hardirqs_off() also invokes > lockdep_hardirqs_off() under the hood. > > OTOH lockdep needs to know about the interrupts disabled state before > enter_from_user_mode(). lockdep_hardirqs_off() is safe to call at this > point. > > Split it so lockdep knows about the state and invoke the tracepoint after > the context is set straight. > > Even if the functions attached to a tracepoint would all be safe to be > called in rcuidle having it split up is still giving a performance > advantage because rcu_read_lock_sched() is avoiding the whole dance of: > > scru_read_lock(); > rcu_irq_enter_irqson(); > ... > rcu_irq_exit_irqson(); > scru_read_unlock(); > > around the tracepoint function invocation just to have the C entry points > of syscalls call enter_from_user_mode() right after the above dance. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > --- > V2: New patch > --- > arch/x86/entry/common.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-)
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
alex.
> --- a/arch/x86/entry/common.c > +++ b/arch/x86/entry/common.c > @@ -60,10 +60,19 @@ static __always_inline void syscall_entr > { > /* > * Usermode is traced as interrupts enabled, but the syscall entry > - * mechanisms disable interrupts. Tell the tracer. > + * mechanisms disable interrupts. Tell lockdep before calling > + * enter_from_user_mode(). This is safe vs. RCU while the > + * tracepoint is not. > */ > - trace_hardirqs_off(); > + lockdep_hardirqs_on(CALLER_ADDR0); > + > enter_from_user_mode(); > + > + /* > + * Tell the tracer about the irq state as well before enabling > + * interrupts. > + */ > + __trace_hardirqs_off(); > local_irq_enable(); > } > >
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