ring-buffer: add counters for commit overrun and nmi dropped entries
The WARN_ON in the ring buffer when a commit is preempted and the buffer is filled by preceding writes can happen in normal operations. The WARN_ON makes it look like a bug, not to mention, because it does not stop tracing and calls printk which can also recurse, this is prone to deadlock (the WARN_ON is not in a position to recurse). This patch removes the WARN_ON and replaces it with a counter that can be retrieved by a tracer. This counter is called commit_overrun. While at it, I added a nmi_dropped counter to count any time an NMI entry is dropped because the NMI could not take the spinlock. [ Impact: prevent deadlock by printing normal case warning ] Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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d6ce96dabe
Коммит
f0d2c681ac
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@ -153,6 +153,8 @@ unsigned long ring_buffer_entries(struct ring_buffer *buffer);
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unsigned long ring_buffer_overruns(struct ring_buffer *buffer);
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unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_nmi_dropped_cpu(struct ring_buffer *buffer, int cpu);
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u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu);
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void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
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@ -402,6 +402,8 @@ struct ring_buffer_per_cpu {
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struct buffer_page *tail_page; /* write to tail */
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struct buffer_page *commit_page; /* committed pages */
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struct buffer_page *reader_page;
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unsigned long nmi_dropped;
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unsigned long commit_overrun;
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unsigned long overrun;
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unsigned long entries;
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u64 write_stamp;
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@ -1216,8 +1218,10 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
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* simply fail.
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*/
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if (unlikely(in_nmi())) {
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if (!__raw_spin_trylock(&cpu_buffer->lock))
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if (!__raw_spin_trylock(&cpu_buffer->lock)) {
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cpu_buffer->nmi_dropped++;
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goto out_reset;
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}
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} else
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__raw_spin_lock(&cpu_buffer->lock);
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@ -1238,8 +1242,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
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* about it.
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*/
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if (unlikely(next_page == commit_page)) {
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/* This can easily happen on small ring buffers */
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WARN_ON_ONCE(buffer->pages > 2);
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cpu_buffer->commit_overrun++;
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goto out_reset;
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}
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@ -1925,6 +1928,47 @@ unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
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}
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EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
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/**
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* ring_buffer_nmi_dropped_cpu - get the number of nmis that were dropped
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* @buffer: The ring buffer
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* @cpu: The per CPU buffer to get the number of overruns from
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*/
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unsigned long ring_buffer_nmi_dropped_cpu(struct ring_buffer *buffer, int cpu)
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{
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struct ring_buffer_per_cpu *cpu_buffer;
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unsigned long ret;
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if (!cpumask_test_cpu(cpu, buffer->cpumask))
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return 0;
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cpu_buffer = buffer->buffers[cpu];
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ret = cpu_buffer->nmi_dropped;
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return ret;
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}
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EXPORT_SYMBOL_GPL(ring_buffer_nmi_dropped_cpu);
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/**
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* ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits
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* @buffer: The ring buffer
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* @cpu: The per CPU buffer to get the number of overruns from
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*/
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unsigned long
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ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
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{
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struct ring_buffer_per_cpu *cpu_buffer;
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unsigned long ret;
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if (!cpumask_test_cpu(cpu, buffer->cpumask))
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return 0;
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cpu_buffer = buffer->buffers[cpu];
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ret = cpu_buffer->commit_overrun;
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return ret;
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}
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EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
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/**
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* ring_buffer_entries - get the number of entries in a buffer
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* @buffer: The ring buffer
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@ -2595,6 +2639,8 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
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local_set(&cpu_buffer->reader_page->page->commit, 0);
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cpu_buffer->reader_page->read = 0;
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cpu_buffer->nmi_dropped = 0;
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cpu_buffer->commit_overrun = 0;
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cpu_buffer->overrun = 0;
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cpu_buffer->entries = 0;
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