Merge tag 'trace-ringbuffer-v7.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull ring-buffer fixes from Steven Rostedt:

- Fix reporting MISSED EVENTS in trace iterator

Merge tag 'trace-ringbuffer-v7.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull ring-buffer fixes from Steven Rostedt:

- Fix reporting MISSED EVENTS in trace iterator

When the "trace" file is read with tracing enabled, if the writer
were to pass the iterator reader, it resets, sets a "missed_events"
flag and continues. The tracing output checks for missed events and
if there are some, it prints out "[LOST EVENTS]" to let the user know
events were dropped.

But the clearing of the missed_events happened when the tracing
system queried the ring buffer iterator about missed events. This was
premature as the ring buffer is per CPU, and the tracing code reads
all the CPU buffers and checks for missed events when it is read. If
the CPU iterator that had missed events isn't printed next, the
output for the LOST EVENTS is lost.

Clear the missed_events flag when the iterator moves to the next
event and not when the missed_events flag is queried. Also clear it
on reset.

- Flush and stop the persistent ring buffer on panic

On panic the persistent ring buffer is used to debug what caused the
panic. But on some architectures, it requires flushing the memory
from cache, otherwise, the ring buffer persistent memory may not have
the last events and this could also cause the ring buffer to be
corrupted on the next boot.

- Fix nr_subbufs initialization in simple_ring_buffer_init_mm

The remote simple ring buffer meta data nr_subbufs is initialized too
early and gets cleared later on, making it zero and not reflect the
actual number of sub-buffers.

- Fix unload_page for simple_ring_buffer init rollback

On error, the pages loaded need to be unloaded. To unload a page it
is expected that: page = load_page(va); -> unload_page(page). But the
code was doing: unload_page(va) and not unload_page(page).

- Create output file from cmd_check_undefined

The check for undefined symbols checks if the file *.o.checked exists
and if so it skips doing the work. But the *.o.checked file never was
created making every build do the work even when it was already done
previously.

* tag 'trace-ringbuffer-v7.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Create output file from cmd_check_undefined
tracing: Fix unload_page for simple_ring_buffer init rollback
tracing: Fix nr_subbufs initialization in simple_ring_buffer_init_mm()
ring-buffer: Flush and stop persistent ring buffer on panic
ring-buffer: Fix reporting of missed events in iterator

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ring-buffer: Flush and stop persistent ring buffer on panic

On real hardware, panic and machine reboot may not flush hardware cache
to memory. This means the persistent ring buffer, which relies on

ring-buffer: Flush and stop persistent ring buffer on panic

On real hardware, panic and machine reboot may not flush hardware cache
to memory. This means the persistent ring buffer, which relies on a
coherent state of memory, may not have its events written to the buffer
and they may be lost. Moreover, there may be inconsistency with the
counters which are used for validation of the integrity of the
persistent ring buffer which may cause all data to be discarded.

To avoid this issue, stop recording of the ring buffer on panic and
flush the cache of the ring buffer's memory.

Fixes: e645535a954a ("tracing: Add option to use memmapped memory for trace boot instance")
Cc: stable@vger.kernel.org
Cc: Will Deacon <will@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ian Rogers <irogers@google.com>
Link: https://patch.msgid.link/177751969602.2136606.12031934362587643488.stgit@mhiramat.tok.corp.google.com
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

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