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ring-buffer: add counters for commit overrun and nmi dropped entries

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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>
This commit is contained in:
Steven Rostedt 2009-04-29 13:43:37 -04:00 committed by Steven Rostedt
parent d6ce96dabe
commit f0d2c681ac
2 changed files with 51 additions and 3 deletions
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2
include/linux/ring_buffer.h
View file

@ -153,6 +153,8 @@ unsigned long ring_buffer_entries(struct ring_buffer *buffer);
unsigned long ring_buffer_overruns(struct ring_buffer *buffer);
unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu);
unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu);
unsigned long ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu);
unsigned long ring_buffer_nmi_dropped_cpu(struct ring_buffer *buffer, int cpu);
u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu);
void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,

52
kernel/trace/ring_buffer.c
View file

@ -402,6 +402,8 @@ struct ring_buffer_per_cpu {
struct buffer_page *tail_page; /* write to tail */
struct buffer_page *commit_page; /* committed pages */
struct buffer_page *reader_page;
unsigned long nmi_dropped;
unsigned long commit_overrun;
unsigned long overrun;
unsigned long entries;
u64 write_stamp;
@ -1216,8 +1218,10 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
* simply fail.
*/
if (unlikely(in_nmi())) {
if (!__raw_spin_trylock(&cpu_buffer->lock))
if (!__raw_spin_trylock(&cpu_buffer->lock)) {
cpu_buffer->nmi_dropped++;
goto out_reset;
}
} else
__raw_spin_lock(&cpu_buffer->lock);
@ -1238,8 +1242,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
* about it.
*/
if (unlikely(next_page == commit_page)) {
/* This can easily happen on small ring buffers */
WARN_ON_ONCE(buffer->pages > 2);
cpu_buffer->commit_overrun++;
goto out_reset;
}
@ -1925,6 +1928,47 @@ unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
}
EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
/**
* ring_buffer_nmi_dropped_cpu - get the number of nmis that were dropped
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of overruns from
*/
unsigned long ring_buffer_nmi_dropped_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = cpu_buffer->nmi_dropped;
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_nmi_dropped_cpu);
/**
* ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of overruns from
*/
unsigned long
ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = cpu_buffer->commit_overrun;
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
/**
* ring_buffer_entries - get the number of entries in a buffer
* @buffer: The ring buffer
@ -2595,6 +2639,8 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
local_set(&cpu_buffer->reader_page->page->commit, 0);
cpu_buffer->reader_page->read = 0;
cpu_buffer->nmi_dropped = 0;
cpu_buffer->commit_overrun = 0;
cpu_buffer->overrun = 0;
cpu_buffer->entries = 0;