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perf sched: Replace (void*)1 sentinel with proper runtime allocation

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map__findnew_thread() marks color-pid threads by storing (void*)1 as
the thread private data via thread__set_priv().  This sentinel value
causes two problems:

1. thread__get_runtime() returns (void*)1 as a struct thread_runtime
   pointer.  Any field access (e.g. tr->shortname) dereferences address
   1, which is an unmapped page — immediate segfault.

2. cmd_sched() registers free() as the thread priv destructor, so thread
   cleanup calls free((void*)1) — undefined behavior that corrupts the
   heap on many allocators.

Fix by adding a 'color' flag to struct thread_runtime and allocating a
real runtime struct for color-pid threads.  thread__has_color() now
checks the flag instead of relying on priv being non-NULL.

Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Fixes: 58a606149c ("perf sched: Avoid union type punning undefined behavior")
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Ian Rogers <irogers@google.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Arnaldo Carvalho de Melo
2026-06-10 21:00:11 -03:00
parent cfafef390c
commit 500f5dd0a8
1 changed files with 17 additions and 6 deletions
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23
tools/perf/builtin-sched.c
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@@ -274,6 +274,7 @@ struct thread_runtime {
u64 migrations;
int prio;
bool color;
};
/* per event run time data */
@@ -1589,22 +1590,32 @@ static int process_sched_wakeup_ignore(const struct perf_tool *tool __maybe_unus
static bool thread__has_color(struct thread *thread)
{
return thread__priv(thread) != NULL;
struct thread_runtime *tr = thread__priv(thread);
return tr != NULL && tr->color;
}
static struct thread*
map__findnew_thread(struct perf_sched *sched, struct machine *machine, pid_t pid, pid_t tid)
{
struct thread *thread = machine__findnew_thread(machine, pid, tid);
bool color = false;
if (!sched->map.color_pids || !thread || thread__priv(thread))
if (!sched->map.color_pids || !thread)
return thread;
if (thread_map__has(sched->map.color_pids, tid))
color = true;
/*
* Always check the color-pids map, even if thread__priv() is
* already set. COMM events processed before the first sched_switch
* allocate a thread_runtime via thread__get_runtime(), so priv is
* non-NULL before we ever get here. Skipping the check on non-NULL
* priv would prevent those threads from being colored.
*/
if (thread_map__has(sched->map.color_pids, tid)) {
struct thread_runtime *tr = thread__get_runtime(thread);
thread__set_priv(thread, color ? ((void*)1) : NULL);
if (tr)
tr->color = true;
}
return thread;
}