Messages in this thread Patch in this message | | | Date | Sun, 08 Mar 2020 23:24:08 +0100 | From | Thomas Gleixner <> | Subject | [patch part-II V2 09/13] x86/entry/common: Split hardirq tracing into lockdep and ftrace parts |
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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(-)
--- 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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