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perf lock contention: Fix SIGCHLD vs pause() race in __cmd_contention()

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__cmd_contention() suffers from the same lost-wakeup race as the perf
sched stats paths: SIGCHLD can be consumed by the signal handler
before pause() is entered, hanging the process.

Apply the same fix: replace pause() with a loop checking the 'done'
flag and using waitpid(WNOHANG) for the workload case.

Suggested-by: Namhyung Kim <namhyung@kernel.org>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Swapnil Sapkal 2026-05-20 10:20:17 +00:00 committed by Arnaldo Carvalho de Melo
parent 5b8c90e066
commit 35c9fb2200
1 changed files with 10 additions and 2 deletions
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12
tools/perf/builtin-lock.c
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@ -31,6 +31,7 @@
#include <stdio.h>
#include <sys/types.h>
#include <sys/prctl.h>
#include <sys/wait.h>
#include <semaphore.h>
#include <math.h>
#include <limits.h>
@ -1915,8 +1916,11 @@ static int __cmd_report(bool display_info)
return err;
}
static volatile sig_atomic_t done;
static void sighandler(int sig __maybe_unused)
{
done = 1;
}
static int check_lock_contention_options(const struct option *options,
@ -2054,6 +2058,7 @@ static int __cmd_contention(int argc, const char **argv)
goto out_delete;
}
done = 0;
signal(SIGINT, sighandler);
signal(SIGCHLD, sighandler);
signal(SIGTERM, sighandler);
@ -2121,8 +2126,11 @@ static int __cmd_contention(int argc, const char **argv)
if (argc)
evlist__start_workload(con.evlist);
/* wait for signal */
pause();
while (!done) {
if (argc && waitpid(con.evlist->workload.pid, NULL, WNOHANG) > 0)
break;
sleep(1);
}
lock_contention_stop();
lock_contention_read(&con);