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authorLinus Torvalds <torvalds@linux-foundation.org>2019-05-15 16:05:47 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-05-15 16:05:47 -0700
commitd2d8b146043ae7e250aef1fb312971f6f479d487 (patch)
tree22db8758a5aa0bc850ba8f83fe57b1f679924d0a /Documentation
parent2bbacd1a92788ee334c7e92b765ea16ebab68dfe (diff)
parent693713cbdb3a4bda5a8a678c31f06560bbb14657 (diff)
Merge tag 'trace-v5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing updates from Steven Rostedt: "The major changes in this tracing update includes: - Removal of non-DYNAMIC_FTRACE from 32bit x86 - Removal of mcount support from x86 - Emulating a call from int3 on x86_64, fixes live kernel patching - Consolidated Tracing Error logs file Minor updates: - Removal of klp_check_compiler_support() - kdb ftrace dumping output changes - Accessing and creating ftrace instances from inside the kernel - Clean up of #define if macro - Introduction of TRACE_EVENT_NOP() to disable trace events based on config options And other minor fixes and clean ups" * tag 'trace-v5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (44 commits) x86: Hide the int3_emulate_call/jmp functions from UML livepatch: Remove klp_check_compiler_support() ftrace/x86: Remove mcount support ftrace/x86_32: Remove support for non DYNAMIC_FTRACE tracing: Simplify "if" macro code tracing: Fix documentation about disabling options using trace_options tracing: Replace kzalloc with kcalloc tracing: Fix partial reading of trace event's id file tracing: Allow RCU to run between postponed startup tests tracing: Fix white space issues in parse_pred() function tracing: Eliminate const char[] auto variables ring-buffer: Fix mispelling of Calculate tracing: probeevent: Fix to make the type of $comm string tracing: probeevent: Do not accumulate on ret variable tracing: uprobes: Re-enable $comm support for uprobe events ftrace/x86_64: Emulate call function while updating in breakpoint handler x86_64: Allow breakpoints to emulate call instructions x86_64: Add gap to int3 to allow for call emulation tracing: kdb: Allow ftdump to skip all but the last few entries tracing: Add trace_total_entries() / trace_total_entries_cpu() ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/trace/ftrace.rst31
-rw-r--r--Documentation/trace/histogram.rst16
2 files changed, 33 insertions, 14 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index c3b9bd2fd512..f60079259669 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -765,6 +765,37 @@ Here is the list of current tracers that may be configured.
tracers from tracing simply echo "nop" into
current_tracer.
+Error conditions
+----------------
+
+ For most ftrace commands, failure modes are obvious and communicated
+ using standard return codes.
+
+ For other more involved commands, extended error information may be
+ available via the tracing/error_log file. For the commands that
+ support it, reading the tracing/error_log file after an error will
+ display more detailed information about what went wrong, if
+ information is available. The tracing/error_log file is a circular
+ error log displaying a small number (currently, 8) of ftrace errors
+ for the last (8) failed commands.
+
+ The extended error information and usage takes the form shown in
+ this example::
+
+ # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
+ echo: write error: Invalid argument
+
+ # cat /sys/kernel/debug/tracing/error_log
+ [ 5348.887237] location: error: Couldn't yyy: zzz
+ Command: xxx
+ ^
+ [ 7517.023364] location: error: Bad rrr: sss
+ Command: ppp qqq
+ ^
+
+ To clear the error log, echo the empty string into it::
+
+ # echo > /sys/kernel/debug/tracing/error_log
Examples of using the tracer
----------------------------
diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst
index ddbaffa530f9..fb621a1c2638 100644
--- a/Documentation/trace/histogram.rst
+++ b/Documentation/trace/histogram.rst
@@ -199,20 +199,8 @@ Extended error information
For some error conditions encountered when invoking a hist trigger
command, extended error information is available via the
- corresponding event's 'hist' file. Reading the hist file after an
- error will display more detailed information about what went wrong,
- if information is available. This extended error information will
- be available until the next hist trigger command for that event.
-
- If available for a given error condition, the extended error
- information and usage takes the following form::
-
- # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
- echo: write error: Invalid argument
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist
- ERROR: Couldn't yyy: zzz
- Last command: xxx
+ tracing/error_log file. See Error Conditions in
+ :file:`Documentation/trace/ftrace.rst` for details.
6.2 'hist' trigger examples
---------------------------