lkml.org 
[lkml]   [2020]   [May]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[patch V4 part 1 34/36] sched,rcu,tracing: Avoid tracing before in_nmi() is correct
    From: Peter Zijlstra <peterz@infradead.org>

    If a tracer is invoked before in_nmi() becomes true, the tracer can no
    longer detect it is called from NMI context and behave correctly.

    Therefore change nmi_{enter,exit}() to use __preempt_count_{add,sub}()
    as the normal preempt_count_{add,sub}() have a (desired) function
    trace entry.

    This fixes a potential issue with the current code; when the function-tracer
    has stack-tracing enabled __trace_stack() will malfunction when it hits the
    preempt_count_add() function entry from NMI context.

    Suggested-by: Steven Rostedt (VMware) <rosted@goodmis.org>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    ---
    include/linux/hardirq.h | 13 +++++++++++--
    1 file changed, 11 insertions(+), 2 deletions(-)

    --- a/include/linux/hardirq.h
    +++ b/include/linux/hardirq.h
    @@ -66,6 +66,15 @@ extern void irq_exit(void);
    #endif

    /*
    + * NMI vs Tracing
    + * --------------
    + *
    + * We must not land in a tracer until (or after) we've changed preempt_count
    + * such that in_nmi() becomes true. To that effect all NMI C entry points must
    + * be marked 'notrace' and call nmi_enter() as soon as possible.
    + */
    +
    +/*
    * nmi_enter() can nest up to 15 times; see NMI_BITS.
    */
    #define nmi_enter() \
    @@ -75,7 +84,7 @@ extern void irq_exit(void);
    lockdep_off(); \
    ftrace_nmi_enter(); \
    BUG_ON(in_nmi() == NMI_MASK); \
    - preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \
    + __preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \
    rcu_nmi_enter(); \
    lockdep_hardirq_enter(); \
    } while (0)
    @@ -85,7 +94,7 @@ extern void irq_exit(void);
    lockdep_hardirq_exit(); \
    rcu_nmi_exit(); \
    BUG_ON(!in_nmi()); \
    - preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \
    + __preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \
    ftrace_nmi_exit(); \
    lockdep_on(); \
    printk_nmi_exit(); \
    \
     
     \ /
      Last update: 2020-05-05 16:15    [W:7.061 / U:0.324 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site