diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/ring_buffer.c | 64 |
1 files changed, 17 insertions, 47 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 81279c6602ff..f6ee9b1ef62a 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2538,61 +2538,29 @@ rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer) * The lock and unlock are done within a preempt disable section. * The current_context per_cpu variable can only be modified * by the current task between lock and unlock. But it can - * be modified more than once via an interrupt. To pass this - * information from the lock to the unlock without having to - * access the 'in_interrupt()' functions again (which do show - * a bit of overhead in something as critical as function tracing, - * we use a bitmask trick. + * be modified more than once via an interrupt. There are four + * different contexts that we need to consider. * - * bit 0 = NMI context - * bit 1 = IRQ context - * bit 2 = SoftIRQ context - * bit 3 = normal context. + * Normal context. + * SoftIRQ context + * IRQ context + * NMI context * - * This works because this is the order of contexts that can - * preempt other contexts. A SoftIRQ never preempts an IRQ - * context. - * - * When the context is determined, the corresponding bit is - * checked and set (if it was set, then a recursion of that context - * happened). - * - * On unlock, we need to clear this bit. To do so, just subtract - * 1 from the current_context and AND it to itself. - * - * (binary) - * 101 - 1 = 100 - * 101 & 100 = 100 (clearing bit zero) - * - * 1010 - 1 = 1001 - * 1010 & 1001 = 1000 (clearing bit 1) - * - * The least significant bit can be cleared this way, and it - * just so happens that it is the same bit corresponding to - * the current context. + * If for some reason the ring buffer starts to recurse, we + * only allow that to happen at most 4 times (one for each + * context). If it happens 5 times, then we consider this a + * recusive loop and do not let it go further. */ static __always_inline int trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer) { - unsigned int val = cpu_buffer->current_context; - int bit; - - if (in_interrupt()) { - if (in_nmi()) - bit = RB_CTX_NMI; - else if (in_irq()) - bit = RB_CTX_IRQ; - else - bit = RB_CTX_SOFTIRQ; - } else - bit = RB_CTX_NORMAL; - - if (unlikely(val & (1 << bit))) + if (cpu_buffer->current_context >= 4) return 1; - val |= (1 << bit); - cpu_buffer->current_context = val; + cpu_buffer->current_context++; + /* Interrupts must see this update */ + barrier(); return 0; } @@ -2600,7 +2568,9 @@ trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer) static __always_inline void trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer) { - cpu_buffer->current_context &= cpu_buffer->current_context - 1; + /* Don't let the dec leak out */ + barrier(); + cpu_buffer->current_context--; } /** |