linux.git/kernel/trace, branch master

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

2026-05-22T13:09:58+00:00

Pull tracing fixes from Steven Rostedt:

 - Avoid NULL return from hist_field_name()

   The function hist_field_name() is directly passed to a strcat() which
   does not handle "NULL" characters. Return a zero length string when
   size is greater than the limit.

   This is used only to output already created histograms and no field
   currently is greater than the limit. But it should still not return
   NULL.

 - Do not call map->ops->elt_free() on allocation failure

   When elt_alloc() fails, it should not call the map->ops->elt_free()
   function if it exists, as that function may not be able to handle the
   free on allocation failures. The ->elt_free() should only be called
   when elt_alloc() succeeds.

* tag 'trace-v7.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  tracing: Do not call map->ops->elt_free() if elt_alloc() fails
  tracing: Avoid NULL return from hist_field_name() on truncation

tracing: Do not call map->ops->elt_free() if elt_alloc() fails

2026-05-21T15:29:03+00:00

In paths where tracing_map_elt_alloc() failed to allocate objects,
the map->ops->elt_alloc() call was never successful. In this case,
map->ops->elt_free() should not be called.

Link: https://sashiko.dev/#/patchset/20260520223101.34710-1-rosenp%40gmail.com

Cc: stable@vger.kernel.org
Cc: Tom Zanussi 
Cc: Mathieu Desnoyers 
Cc: Rosen Penev 
Reported-by: Sashiko 
Fixes: 2734b629525a ("tracing: Add per-element variable support to tracing_map")
Link: https://patch.msgid.link/177933895460.108746.5396070821443932634.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) 
Signed-off-by: Steven Rostedt

tracing: Create output file from cmd_check_undefined

2026-05-21T12:31:55+00:00

As the output file is currently never created, the check will run every
time, even if the inputs have not changed.

Create an empty output file which allows make to skip the execution when
it is not necessary.

Cc: Masami Hiramatsu 
Cc: Mathieu Desnoyers 
Cc: Vincent Donnefort 
Cc: Marc Zyngier 
Cc: Arnd Bergmann 
Link: https://patch.msgid.link/20260520-tracing-ringbuffer-check-v1-1-d979cfab1338@weissschuh.net
Fixes: 1211907ac0b5 ("tracing: Generate undef symbols allowlist for simple_ring_buffer")
Fixes: 58b4bd18390e ("tracing: Adjust cmd_check_undefined to show unexpected undefined symbols")
Reviewed-by: Nathan Chancellor 
Tested-by: Nathan Chancellor 
Signed-off-by: Thomas Weißschuh 
Signed-off-by: Steven Rostedt

tracing: Fix unload_page for simple_ring_buffer init rollback

2026-05-21T12:26:22+00:00

The unload_page callback expects the return value of load_page() as its
argument: ret = load_page(va); unload(ret). Fix the rollback code in
simple_ring_buffer_init_mm() where the descriptor's VA is used instead
of the loaded page address.

Link: https://patch.msgid.link/20260512141614.1759430-1-vdonnefort@google.com
Fixes: 635923081c79 ("tracing: load/unload page callbacks for simple_ring_buffer")
Signed-off-by: Vincent Donnefort 
Signed-off-by: Steven Rostedt

tracing: Fix nr_subbufs initialization in simple_ring_buffer_init_mm()

2026-05-21T12:24:59+00:00

nr_subbufs in the ring buffer metadata is always initialized to zero
because it is assigned from cpu_buffer->nr_pages before the page
initialization loop has run. While nr_subbufs is not currently read
by the kernel, it should reflect the actual buffer geometry in the
meta page for correctness.

Move the assignment after the page loop so that cpu_buffer->nr_pages
holds the final count.

Link: https://patch.msgid.link/20260512135420.99194-1-devnexen@gmail.com
Fixes: 34e5b958bdad ("tracing: Introduce simple_ring_buffer")
Reviewed-by: Vincent Donnefort 
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: David Carlier 
Signed-off-by: Steven Rostedt

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

2026-05-21T12:20:58+00:00

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 
Cc: Mathieu Desnoyers 
Cc: Ian Rogers 
Link: https://patch.msgid.link/177751969602.2136606.12031934362587643488.stgit@mhiramat.tok.corp.google.com
Signed-off-by: Masami Hiramatsu (Google) 
Acked-by: Catalin Marinas 
Acked-by: Geert Uytterhoeven 
Signed-off-by: Steven Rostedt

ring-buffer: Fix reporting of missed events in iterator

2026-05-21T12:20:29+00:00

When tracing is active while reading the trace file, if the iterator
reading the buffer detects that the writer has passed the iterator head,
it will reset and set a "missed events" flag. This flag is passed to the
output processing to show the user that events were missed:

  CPU:4 [LOST EVENTS]

The problem is that the flag is reset after it is checked in
ring_buffer_iter_dropped(). But the "trace" file iterates over all the CPU
ring buffers and it will check if they are dropped when figuring out which
buffer to print next. This prematurely clears the missed_events flag if
the CPU buffer with the missed events is not the one that is printed next.

On the iteration where the CPU buffer with the missed events is printed,
the check if it had missed events would return false and the output does
not show that events were missed.

Do not reset the missed_events flag when checking if there were missed
events, but instead clear it when moving the iterator head to the next
event.

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers 
Link: https://patch.msgid.link/20260520220801.4fd09d13@fedora
Fixes: c9b7a4a72ff64 ("ring-buffer/tracing: Have iterator acknowledge dropped events")
Acked-by: Masami Hiramatsu (Google) 
Signed-off-by: Steven Rostedt

tracing: Avoid NULL return from hist_field_name() on truncation

2026-05-20T20:10:56+00:00

hist_field_name() returns "" everywhere except the fully-qualified
VAR_REF/EXPR case, where snprintf() truncation returns NULL early
and bypasses the bottom NULL->"" guard. Callers don't expect NULL:
strcat(expr, hist_field_name(field, 0)) at trace_events_hist.c:1758
and the strcmp() in the sort-key match loop at :4804 both deref it.

system and event_name are bounded by MAX_EVENT_NAME_LEN, but the
field name on a VAR_REF is kstrdup'd from a histogram variable
name parsed out of the trigger string and has no length cap, so
a long enough var name in a fully qualified reference can reach
the truncation path.

Keep the length check but leave field_name as "" on overflow.

Link: https://patch.msgid.link/20260508195747.25492-1-devnexen@gmail.com
Fixes: 5ec1d1e97de1 ("tracing: Rebuild full_name on each hist_field_name() call")
Signed-off-by: David Carlier 
Signed-off-by: Steven Rostedt

Merge tag 'trace-v7.1-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

2026-05-17T19:02:31+00:00

Pull tracing fixes from Steven Rostedt:

 - Add more functions to the remote allowed list

   randconfig found more functions that are allowed for the remote code
   for s390 and arm. Add them to the allowed list.

 - Fix remote_test error path

   If one of the simple ring buffers fails to load, the code is supposed
   to rollback its initialized buffers. Instead of rolling back the
   buffers for the failed load, it uses the global variable and rolls
   back all the successfully loaded buffers.

* tag 'trace-v7.1-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  tracing: Fix desc in error path for the trace remote test module
  ring-buffer remote: Avoid unexpected symbol warnings (arm, s390)

tracing: Fix desc in error path for the trace remote test module

2026-05-16T20:11:04+00:00

During initialisation in remote_test_load(), if one of the
simple_ring_buffer fails to initialise, the error path attempts to
rollback initialised buffers. However, the rollback incorrectly uses the
global pointer to the trace descriptor, which is only set upon
successful load completion. Fix the error path by using the local
pointer to the descriptor.

Link: https://patch.msgid.link/20260515201616.337469-1-vdonnefort@google.com
Fixes: ea908a2b79c8 ("tracing: Add a trace remote module for testing")
Reported-by: Sashiko 
Signed-off-by: Vincent Donnefort 

base-commit: 5d6919055dec134de3c40167a490f33c74c12581
Signed-off-by: Steven Rostedt