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tracing: Limit the shooting in the foot of tp_printk

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The "tp_printk" option redirects the trace event output to printk at boot
 up. This is useful when a machine crashes before boot where the trace events
 can not be retrieved by the in kernel ring buffer. But it can be "dangerous"
 because trace events can be located in high frequency locations such as
 interrupts and the scheduler, where a printk can slow it down that it live
 locks the machine (because by the time the printk finishes, the next event
 is triggered). Thus tp_printk must be used with care.
 
 It was discovered that the filter logic to trace events does not apply to
 the tp_printk events. This can cause a surprise and live lock when the user
 expects it to be filtered to limit the amount of events printed to the
 console when in fact it still prints everything.
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Merge tag 'trace-v5.14-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fix from Steven Rostedt:
 "Limit the shooting in the foot of tp_printk

  The "tp_printk" option redirects the trace event output to printk at
  boot up. This is useful when a machine crashes before boot where the
  trace events can not be retrieved by the in kernel ring buffer. But it
  can be "dangerous" because trace events can be located in high
  frequency locations such as interrupts and the scheduler, where a
  printk can slow it down that it live locks the machine (because by the
  time the printk finishes, the next event is triggered). Thus tp_printk
  must be used with care.

  It was discovered that the filter logic to trace events does not apply
  to the tp_printk events. This can cause a surprise and live lock when
  the user expects it to be filtered to limit the amount of events
  printed to the console when in fact it still prints everything"

* tag 'trace-v5.14-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Apply trace filters on all output channels
This commit is contained in:
Linus Torvalds 2021-08-17 09:47:18 -10:00
commit 614cb2751d
2 changed files with 15 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
kernel/trace/trace.c
View File

@ -2897,14 +2897,26 @@ int tracepoint_printk_sysctl(struct ctl_table *table, int write,
void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
{
enum event_trigger_type tt = ETT_NONE;
struct trace_event_file *file = fbuffer->trace_file;
if (__event_trigger_test_discard(file, fbuffer->buffer, fbuffer->event,
fbuffer->entry, &tt))
goto discard;
if (static_key_false(&tracepoint_printk_key.key))
output_printk(fbuffer);
if (static_branch_unlikely(&trace_event_exports_enabled))
ftrace_exports(fbuffer->event, TRACE_EXPORT_EVENT);
event_trigger_unlock_commit_regs(fbuffer->trace_file, fbuffer->buffer,
fbuffer->event, fbuffer->entry,
fbuffer->trace_ctx, fbuffer->regs);
trace_buffer_unlock_commit_regs(file->tr, fbuffer->buffer,
fbuffer->event, fbuffer->trace_ctx, fbuffer->regs);
discard:
if (tt)
event_triggers_post_call(file, tt);
}
EXPORT_SYMBOL_GPL(trace_event_buffer_commit);

32
kernel/trace/trace.h
View File

@ -1389,38 +1389,6 @@ event_trigger_unlock_commit(struct trace_event_file *file,
event_triggers_post_call(file, tt);
}
/**
* event_trigger_unlock_commit_regs - handle triggers and finish event commit
* @file: The file pointer associated with the event
* @buffer: The ring buffer that the event is being written to
* @event: The event meta data in the ring buffer
* @entry: The event itself
* @trace_ctx: The tracing context flags.
*
* This is a helper function to handle triggers that require data
* from the event itself. It also tests the event against filters and
* if the event is soft disabled and should be discarded.
*
* Same as event_trigger_unlock_commit() but calls
* trace_buffer_unlock_commit_regs() instead of trace_buffer_unlock_commit().
*/
static inline void
event_trigger_unlock_commit_regs(struct trace_event_file *file,
struct trace_buffer *buffer,
struct ring_buffer_event *event,
void *entry, unsigned int trace_ctx,
struct pt_regs *regs)
{
enum event_trigger_type tt = ETT_NONE;
if (!__event_trigger_test_discard(file, buffer, event, entry, &tt))
trace_buffer_unlock_commit_regs(file->tr, buffer, event,
trace_ctx, regs);
if (tt)
event_triggers_post_call(file, tt);
}
#define FILTER_PRED_INVALID ((unsigned short)-1)
#define FILTER_PRED_IS_RIGHT (1 << 15)
#define FILTER_PRED_FOLD (1 << 15)