Messages in this thread Patch in this message | | | Date | Mon, 14 Mar 2011 19:06:21 +0100 | From | Jiri Olsa <> | Subject | [PATCHv2] tracing - avoid soft lockup in trace_pipe |
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On Mon, Mar 14, 2011 at 11:20:57AM -0400, Steven Rostedt wrote: > On Mon, 2011-03-14 at 16:07 +0100, Jiri Olsa wrote: > > So we get back the the while loop with no data added and with > > TRACE_TYPE_HANDLED return code, which will keep us in the loop. > > > > Not sure this is bug or feature :) > > > > > Most bugs are features ;) > > honestly, I'd love to rip out all the "bin", "hex" etc formats as they > are pretty much deprecated. > > But as you pointed out that this can keep us in the inner loop, we need > to fix that. I prefer to fix it within the nop print function. Perhaps > we need to fill in something. "type: %d", iter->ent->type ?
sounds ok :) attaching v2 patch
thanks, jirka
--- running following commands:
# enable the binary option echo 1 > ./options/bin # disable context info option echo 0 > ./options/context-info # tracing only events echo 1 > ./events/enable cat trace_pipe
is causing lockup (in NON preemptive kernels) inside tracing_read_pipe function.
The reason are: - bin/hex/raw output functions for events are set to trace_nop_print function, which prints nothing and returns TRACE_TYPE_HANDLED value - LOST EVENT trace do not handle trace_seq overflow
These reasons force the while loop in tracing_read_pipe function never to break.
The attached patch fixies handling of lost event trace, and changes trace_nop_print to print minimal info, which is needed for the correct tracing_read_pipe processing.
v2 changes: - omit the cond_resched changes by trace_nop_print changes - WARN changed to WARN_ONCE and added info to be able to find out the culprit
wbr, jirka
Signed-off-by: Jiri Olsa <jolsa@redhat.com> --- kernel/trace/trace.c | 15 ++++++++++++--- kernel/trace/trace_output.c | 3 +++ 2 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 9541c27..5af42f4 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2013,9 +2013,10 @@ enum print_line_t print_trace_line(struct trace_iterator *iter) { enum print_line_t ret; - if (iter->lost_events) - trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n", - iter->cpu, iter->lost_events); + if (iter->lost_events && + !trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n", + iter->cpu, iter->lost_events)) + return TRACE_TYPE_PARTIAL_LINE; if (iter->trace && iter->trace->print_line) { ret = iter->trace->print_line(iter); @@ -3229,6 +3230,14 @@ waitagain: if (iter->seq.len >= cnt) break; + + /* + * Setting the full flag means we reached the trace_seq buffer + * size and we should leave by partial output condition above. + * One of the trace_seq_* functions is not used properly. + */ + WARN_ONCE(iter->seq.full, "full flag set for trace type %d", + iter->ent->type); } trace_access_unlock(iter->cpu_file); trace_event_read_unlock(); diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index 456be90..cf535cc 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -830,6 +830,9 @@ EXPORT_SYMBOL_GPL(unregister_ftrace_event); enum print_line_t trace_nop_print(struct trace_iterator *iter, int flags, struct trace_event *event) { + if (!trace_seq_printf(&iter->seq, "type: %d\n", iter->ent->type)) + return TRACE_TYPE_PARTIAL_LINE; + return TRACE_TYPE_HANDLED; } -- 1.7.1
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