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tracing: Choose static tp_printk buffer by explicit nesting count

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Currently, the trace_printk code chooses which static buffer to use based
on what type of atomic context (NMI, IRQ, etc) it's in.  Simplify the
code and make it more robust: simply count the nesting depth and choose
a buffer based on the current nesting depth.

The new code will only drop an event if we nest more than 4 deep,
and the old code was guaranteed to malfunction if that happened.

Link: http://lkml.kernel.org/r/07ab03aecfba25fcce8f9a211b14c9c5e2865c58.1464289095.git.luto@kernel.org

Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Andy Lutomirski 2016-05-26 12:00:33 -07:00 committed by Steven Rostedt
parent 35abb67de7
commit e2ace00117
1 changed files with 24 additions and 59 deletions
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81
kernel/trace/trace.c
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@ -2339,83 +2339,41 @@ static void __trace_userstack(struct trace_array *tr, unsigned long flags)
/* created for use with alloc_percpu */
struct trace_buffer_struct {
char buffer[TRACE_BUF_SIZE];
int nesting;
char buffer[4][TRACE_BUF_SIZE];
};
static struct trace_buffer_struct *trace_percpu_buffer;
static struct trace_buffer_struct *trace_percpu_sirq_buffer;
static struct trace_buffer_struct *trace_percpu_irq_buffer;
static struct trace_buffer_struct *trace_percpu_nmi_buffer;
/*
* The buffer used is dependent on the context. There is a per cpu
* buffer for normal context, softirq contex, hard irq context and
* for NMI context. Thise allows for lockless recording.
*
* Note, if the buffers failed to be allocated, then this returns NULL
* Thise allows for lockless recording. If we're nested too deeply, then
* this returns NULL.
*/
static char *get_trace_buf(void)
{
struct trace_buffer_struct *percpu_buffer;
struct trace_buffer_struct *buffer = this_cpu_ptr(trace_percpu_buffer);
/*
* If we have allocated per cpu buffers, then we do not
* need to do any locking.
*/
if (in_nmi())
percpu_buffer = trace_percpu_nmi_buffer;
else if (in_irq())
percpu_buffer = trace_percpu_irq_buffer;
else if (in_softirq())
percpu_buffer = trace_percpu_sirq_buffer;
else
percpu_buffer = trace_percpu_buffer;
if (!percpu_buffer)
if (!buffer || buffer->nesting >= 4)
return NULL;
return this_cpu_ptr(&percpu_buffer->buffer[0]);
return &buffer->buffer[buffer->nesting++][0];
}
static void put_trace_buf(void)
{
this_cpu_dec(trace_percpu_buffer->nesting);
}
static int alloc_percpu_trace_buffer(void)
{
struct trace_buffer_struct *buffers;
struct trace_buffer_struct *sirq_buffers;
struct trace_buffer_struct *irq_buffers;
struct trace_buffer_struct *nmi_buffers;
buffers = alloc_percpu(struct trace_buffer_struct);
if (!buffers)
goto err_warn;
sirq_buffers = alloc_percpu(struct trace_buffer_struct);
if (!sirq_buffers)
goto err_sirq;
irq_buffers = alloc_percpu(struct trace_buffer_struct);
if (!irq_buffers)
goto err_irq;
nmi_buffers = alloc_percpu(struct trace_buffer_struct);
if (!nmi_buffers)
goto err_nmi;
if (WARN(!buffers, "Could not allocate percpu trace_printk buffer"))
return -ENOMEM;
trace_percpu_buffer = buffers;
trace_percpu_sirq_buffer = sirq_buffers;
trace_percpu_irq_buffer = irq_buffers;
trace_percpu_nmi_buffer = nmi_buffers;
return 0;
err_nmi:
free_percpu(irq_buffers);
err_irq:
free_percpu(sirq_buffers);
err_sirq:
free_percpu(buffers);
err_warn:
WARN(1, "Could not allocate percpu trace_printk buffer");
return -ENOMEM;
}
static int buffers_allocated;
@ -2506,7 +2464,7 @@ int trace_vbprintk(unsigned long ip, const char *fmt, va_list args)
tbuffer = get_trace_buf();
if (!tbuffer) {
len = 0;
goto out;
goto out_nobuffer;
}
len = vbin_printf((u32 *)tbuffer, TRACE_BUF_SIZE/sizeof(int), fmt, args);
@ -2532,6 +2490,9 @@ int trace_vbprintk(unsigned long ip, const char *fmt, va_list args)
}
out:
put_trace_buf();
out_nobuffer:
preempt_enable_notrace();
unpause_graph_tracing();
@ -2563,7 +2524,7 @@ __trace_array_vprintk(struct ring_buffer *buffer,
tbuffer = get_trace_buf();
if (!tbuffer) {
len = 0;
goto out;
goto out_nobuffer;
}
len = vscnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args);
@ -2582,7 +2543,11 @@ __trace_array_vprintk(struct ring_buffer *buffer,
__buffer_unlock_commit(buffer, event);
ftrace_trace_stack(&global_trace, buffer, flags, 6, pc, NULL);
}
out:
put_trace_buf();
out_nobuffer:
preempt_enable_notrace();
unpause_graph_tracing();