- Fix sample code that uses trace_array_printk()
The sample code for in kernel use of trace_array (that creates an instance
for use within the kernel) and shows how to use trace_array_printk() that
writes into the created instance, used trace_printk_init_buffers(). But
that function is used to initialize normal trace_printk() and produces the
NOTICE banner which is not needed for use of trace_array_printk(). The
function to initialize that is trace_array_init_printk() that takes the
created trace array instance as a parameter.
Update the sample code to reflect the proper usage.
- Fix preemption count output for stacktrace event
The tracing buffer shows the preempt count level when an event executes.
Because writing the event itself disables preemption, this needs to be
accounted for when recording. The stacktrace event did not account for
this so the output of the stacktrace event showed preemption was disabled
while the event that triggered the stacktrace shows preemption is enabled
and this leads to confusion. Account for preemption being disabled for the
stacktrace event.
The same happened for stack traces triggered by function tracer.
- Fix persistent ring buffer when trace_pipe is used
The ring buffer swaps the reader page with the next page to read from the
write buffer when trace_pipe is used. If there's only a page of data in
the ring buffer, this swap will cause the "commit" pointer (last data
written) to be on the reader page. If more data is written to the buffer,
it is added to the reader page until it falls off back into the write
buffer.
If the system reboots and the commit pointer is still on the reader page,
even if new data was written, the persistent buffer validator will miss
finding the commit pointer because it only checks the write buffer and
does not check the reader page. This causes the validator to fail the
validation and clear the buffer, where the new data is lost.
There was a check for this, but it checked the "head pointer", which was
incorrect, because the "head pointer" always stays on the write buffer and
is the next page to swap out for the reader page. Fix the logic to catch
this case and allow the user to still read the data after reboot.
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Merge tag 'trace-v6.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull tracing fixes from Steven Rostedt:
- Fix sample code that uses trace_array_printk()
The sample code for in kernel use of trace_array (that creates an
instance for use within the kernel) and shows how to use
trace_array_printk() that writes into the created instance, used
trace_printk_init_buffers(). But that function is used to initialize
normal trace_printk() and produces the NOTICE banner which is not
needed for use of trace_array_printk(). The function to initialize
that is trace_array_init_printk() that takes the created trace array
instance as a parameter.
Update the sample code to reflect the proper usage.
- Fix preemption count output for stacktrace event
The tracing buffer shows the preempt count level when an event
executes. Because writing the event itself disables preemption, this
needs to be accounted for when recording. The stacktrace event did
not account for this so the output of the stacktrace event showed
preemption was disabled while the event that triggered the stacktrace
shows preemption is enabled and this leads to confusion. Account for
preemption being disabled for the stacktrace event.
The same happened for stack traces triggered by function tracer.
- Fix persistent ring buffer when trace_pipe is used
The ring buffer swaps the reader page with the next page to read from
the write buffer when trace_pipe is used. If there's only a page of
data in the ring buffer, this swap will cause the "commit" pointer
(last data written) to be on the reader page. If more data is written
to the buffer, it is added to the reader page until it falls off back
into the write buffer.
If the system reboots and the commit pointer is still on the reader
page, even if new data was written, the persistent buffer validator
will miss finding the commit pointer because it only checks the write
buffer and does not check the reader page. This causes the validator
to fail the validation and clear the buffer, where the new data is
lost.
There was a check for this, but it checked the "head pointer", which
was incorrect, because the "head pointer" always stays on the write
buffer and is the next page to swap out for the reader page. Fix the
logic to catch this case and allow the user to still read the data
after reboot.
* tag 'trace-v6.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
ring-buffer: Fix persistent buffer when commit page is the reader page
ftrace: Fix preemption accounting for stacktrace filter command
ftrace: Fix preemption accounting for stacktrace trigger command
tracing: samples: Initialize trace_array_printk() with the correct function
c94d59a126