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This fixes two bugs: 

- The first one is a side effect caused by using SRCU for rcuidle
    tracepoints. It seems that the perf was depending on the rcuidle
    tracepoints to make RCU watch when it wasn't. The real fix will
    bet to have perf use SRCU instead of depending on RCU watching,
    but that can't be done until SRCU is safe to use in NMI context
    (Paul's working on that).
 
  - The second bug fix is for a bug that's been periodically making
    my tests fail randomly for some time. I haven't had time to track
    it down, but finally have. It has to do with stressing NMIs (via perf)
    while enabling or disabling ftrace function handling with lockdep
    enabled. If an interrupt happens and just as it returns, it sets
    lockdep back to "interrupts enabled" but before it returns an NMI
    is triggered, and if this happens while printk_nmi_enter has a
    breakpoint attached to it (because ftrace is converting it to or from
    nop to call fentry), the breakpoint trap also calls into lockdep,
    and since returning from the NMI to a interrupt handler, interrupts
    were disabled when the NMI went off, lockdep keeps its state as
    interrupts disabled when it returns back from the interrupt handler
    where interrupts are enabled. This causes lockdep_assert_irqs_enabled()
    to trigger a false positive.
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Merge tag 'trace-v4.19-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:
 "This fixes two annoying bugs:

   - The first one is a side effect caused by using SRCU for rcuidle
     tracepoints. It seems that the perf was depending on the rcuidle
     tracepoints to make RCU watch when it wasn't.

     The real fix will be to have perf use SRCU instead of depending on
     RCU watching, but that can't be done until SRCU is safe to use in
     NMI context (Paul's working on that).

   - The second bug fix is for a bug that's been periodically making my
     tests fail randomly for some time. I haven't had time to track it
     down, but finally have. It has to do with stressing NMIs (via perf)
     while enabling or disabling ftrace function handling with lockdep
     enabled.

     If an interrupt happens and just as it returns, it sets lockdep
     back to "interrupts enabled" but before it returns an NMI is
     triggered, and if this happens while printk_nmi_enter has a
     breakpoint attached to it (because ftrace is converting it to or
     from nop to call fentry), the breakpoint trap also calls into
     lockdep, and since returning from the NMI to a interrupt handler,
     interrupts were disabled when the NMI went off, lockdep keeps its
     state as interrupts disabled when it returns back from the
     interrupt handler where interrupts are enabled.

     This causes lockdep_assert_irqs_enabled() to trigger a false
     positive"

* tag 'trace-v4.19-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  printk/tracing: Do not trace printk_nmi_enter()
  tracing: Add back in rcu_irq_enter/exit_irqson() for rcuidle tracepoints
This commit is contained in:
Linus Torvalds 2018-09-06 09:06:49 -07:00
parent 5404525b98 d1c392c9e2
commit be65e2595b
2 changed files with 8 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/tracepoint.h
View File

@ -158,8 +158,10 @@ extern void syscall_unregfunc(void);
* For rcuidle callers, use srcu since sched-rcu \
* doesn't work from the idle path. \
*/ \
if (rcuidle) \
if (rcuidle) { \
idx = srcu_read_lock_notrace(&tracepoint_srcu); \
rcu_irq_enter_irqson(); \
} \
\
it_func_ptr = rcu_dereference_raw((tp)->funcs); \
\
@ -171,8 +173,10 @@ extern void syscall_unregfunc(void);
} while ((++it_func_ptr)->func); \
} \
\
if (rcuidle) \
if (rcuidle) { \
rcu_irq_exit_irqson(); \
srcu_read_unlock_notrace(&tracepoint_srcu, idx);\
} \
\
preempt_enable_notrace(); \
} while (0)

4
kernel/printk/printk_safe.c
View File

@ -306,12 +306,12 @@ static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
return printk_safe_log_store(s, fmt, args);
}
void printk_nmi_enter(void)
void notrace printk_nmi_enter(void)
{
this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
}
void printk_nmi_exit(void)
void notrace printk_nmi_exit(void)
{
this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
}