linux-stable.git/kernel/trace, branch v5.15.209

tracing: Avoid NULL return from hist_field_name() on truncation

2026-06-01T15:35:51+00:00

[ Upstream commit 576ec047d20b368b43c4d5db98c4f2e0f3c101ec ]

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 
Signed-off-by: Sasha Levin

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

2026-06-01T15:35:47+00:00

commit 8f0f5c4fb9df0e19a341e0c6ed8dc4fda9124f03 upstream.

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 
Signed-off-by: Greg Kroah-Hartman

ring-buffer: Fix reporting of missed events in iterator

2026-06-01T15:35:47+00:00

commit a254b6d13b0edd6272926674d2afc46d46e496b7 upstream.

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 
Signed-off-by: Greg Kroah-Hartman

tracing: branch: Fix inverted check on stat tracer registration

2026-06-01T15:35:41+00:00

[ Upstream commit 3b75dd76e64a04771861bb5647951c264919e563 ]

init_annotated_branch_stats() and all_annotated_branch_stats() check the
return value of register_stat_tracer() with "if (!ret)", but
register_stat_tracer() returns 0 on success and a negative errno on
failure. The inverted check causes the warning to be printed on every
successful registration, e.g.:

  Warning: could not register annotated branches stats

while leaving real failures silent. The initcall also returned a
hard-coded 1 instead of the actual error.

Invert the check and propagate ret so that the warning fires on real
errors and the initcall reports the correct status.

Cc: Mathieu Desnoyers 
Cc: Ingo Molnar 
Cc: Frederic Weisbecker 
Link: https://patch.msgid.link/20260420-tracing-v1-1-d8f4cd0d6af1@debian.org
Fixes: 002bb86d8d42 ("tracing/ftrace: separate events tracing and stats tracing engine")
Signed-off-by: Breno Leitao 
Acked-by: Masami Hiramatsu (Google) 
Signed-off-by: Steven Rostedt 
Signed-off-by: Sasha Levin

tracing: Rebuild full_name on each hist_field_name() call

2026-06-01T15:35:34+00:00

[ Upstream commit 5ec1d1e97de134beed3a5b08235a60fc1c51af96 ]

hist_field_name() uses a static MAX_FILTER_STR_VAL buffer for fully
qualified variable-reference names, but it currently appends into that
buffer with strcat() without rebuilding it first. As a result, repeated
calls append a new "system.event.field" name onto the previous one,
which can eventually run past the end of full_name.

Build the name with snprintf() on each call and return NULL if the fully
qualified name does not fit in MAX_FILTER_STR_VAL.

Link: https://patch.msgid.link/20260401112224.85582-1-pengpeng@iscas.ac.cn
Fixes: 067fe038e70f ("tracing: Add variable reference handling to hist triggers")
Reviewed-by: Tom Zanussi 
Tested-by: Tom Zanussi 
Signed-off-by: Pengpeng Hou 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin

tracing/probe: reject non-closed empty immediate strings

2026-06-01T15:35:02+00:00

[ Upstream commit 4346be6577aaa04586167402ae87bbdbe32484a4 ]

parse_probe_arg() accepts quoted immediate strings and passes the body
after the opening quote to __parse_imm_string(). That helper currently
computes strlen(str) and immediately dereferences str[len - 1], which
underflows when the body is empty and not closed with double-quotation.

Reject empty non-closed immediate strings before checking for the closing quote.

Link: https://lore.kernel.org/all/20260401160315.88518-1-pengpeng@iscas.ac.cn/

Fixes: a42e3c4de964 ("tracing/probe: Add immediate string parameter support")
Signed-off-by: Pengpeng Hou 
Reviewed-by: Steven Rostedt (Google) 
Signed-off-by: Masami Hiramatsu (Google) 
Signed-off-by: Sasha Levin

tracing: Fix potential deadlock in cpu hotplug with osnoise

2026-04-18T08:33:38+00:00

[ Upstream commit 1f9885732248d22f788e4992c739a98c88ab8a55 ]

The following sequence may leads deadlock in cpu hotplug:

    task1        task2        task3
    -----        -----        -----

 mutex_lock(&interface_lock)

            [CPU GOING OFFLINE]

            cpus_write_lock();
            osnoise_cpu_die();
              kthread_stop(task3);
                wait_for_completion();

                      osnoise_sleep();
                        mutex_lock(&interface_lock);

 cpus_read_lock();

 [DEAD LOCK]

Fix by swap the order of cpus_read_lock() and mutex_lock(&interface_lock).

Cc: stable@vger.kernel.org
Cc: 
Cc: 
Cc: 
Cc: 
Fixes: bce29ac9ce0bb ("trace: Add osnoise tracer")
Link: https://patch.msgid.link/20260326141953414bVSj33dAYktqp9Oiyizq8@zte.com.cn
Reviewed-by: Masami Hiramatsu (Google) 
Signed-off-by: Luo Haiyang 
Signed-off-by: Steven Rostedt (Google) 
[ adapted guard() macros to lock/unlock calls ]
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

tracing: Fix trace_buf_size= cmdline parameter with sizes >= 2G

2026-04-18T08:33:15+00:00

commit d008ba8be8984760e36d7dcd4adbd5a41a645708 upstream.

Some of the sizing logic through tracer_alloc_buffers() uses int
internally, causing unexpected behavior if the user passes a value that
does not fit in an int (on my x86 machine, the result is uselessly tiny
buffers).

Fix by plumbing the parameter's real type (unsigned long) through to the
ring buffer allocation functions, which already use unsigned long.

It has always been possible to create larger ring buffers via the sysfs
interface: this only affects the cmdline parameter.

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu 
Cc: Mathieu Desnoyers 
Link: https://patch.msgid.link/bff42a4288aada08bdf74da3f5b67a2c28b761f8.1772852067.git.calvin@wbinvd.org
Fixes: 73c5162aa362 ("tracing: keep ring buffer to minimum size till used")
Signed-off-by: Calvin Owens 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Greg Kroah-Hartman

tracing: Fix to set write permission to per-cpu buffer_size_kb

2026-03-04T12:20:35+00:00

[ Upstream commit f844282deed7481cf2f813933229261e27306551 ]

Since the per-cpu buffer_size_kb file is writable for changing
per-cpu ring buffer size, the file should have the write access
permission.

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers 
Link: https://patch.msgid.link/177071301597.2293046.11683339475076917920.stgit@mhiramat.tok.corp.google.com
Fixes: 21ccc9cd7211 ("tracing: Disable "other" permission bits in the tracefs files")
Signed-off-by: Masami Hiramatsu (Google) 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin

tracing: Fix false sharing in hwlat get_sample()

2026-03-04T12:20:14+00:00

[ Upstream commit f743435f988cb0cf1f521035aee857851b25e06d ]

The get_sample() function in the hwlat tracer assumes the caller holds
hwlat_data.lock, but this is not actually happening. The result is
unprotected data access to hwlat_data, and in per-cpu mode can result in
false sharing which may show up as false positive latency events.

The specific case of false sharing observed was primarily between
hwlat_data.sample_width and hwlat_data.count. These are separated by
just 8B and are therefore likely to share a cache line. When one thread
modifies count, the cache line is in a modified state so when other
threads read sample_width in the main latency detection loop, they fetch
the modified cache line. On some systems, the fetch itself may be slow
enough to count as a latency event, which could set up a self
reinforcing cycle of latency events as each event increments count which
then causes more latency events, continuing the cycle.

The other result of the unprotected data access is that hwlat_data.count
can end up with duplicate or missed values, which was observed on some
systems in testing.

Convert hwlat_data.count to atomic64_t so it can be safely modified
without locking, and prevent false sharing by pulling sample_width into
a local variable.

One system this was tested on was a dual socket server with 32 CPUs on
each numa node. With settings of 1us threshold, 1000us width, and
2000us window, this change reduced the number of latency events from
500 per second down to approximately 1 event per minute. Some machines
tested did not exhibit measurable latency from the false sharing.

Cc: Masami Hiramatsu 
Cc: Mathieu Desnoyers 
Link: https://patch.msgid.link/20260210074810.6328-1-clord@mykolab.com
Signed-off-by: Colin Lord 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin