libsubcmd: Don't free the usage string

Currently, commands which depend on 'parse_options_subcommand()' don't
show the usage string, and instead show '(null)'

$ ./perf sched
Usage: (null)

-D, --dump-raw-trace dump raw trace in ASCII
-f, --force don't complain, do it
-i, --input <file> input file name
-v, --verbose be more verbose (show symbol address, etc)

'parse_options_subcommand()' is generally expected to initialise the usage
string, with information in the passed 'subcommands[]' array

This behaviour was changed in:

230a7a71f92212e7 ("libsubcmd: Fix parse-options memory leak")

Where the generated usage string is deallocated, and usage[0] string is
reassigned as NULL.

As discussed in [1], free the allocated usage string in the main
function itself, and don't reset usage string to NULL in
parse_options_subcommand

With this change, the behaviour is restored.

$ ./perf sched
Usage: perf sched [<options>] {record|latency|map|replay|script|timehist}

-D, --dump-raw-trace dump raw trace in ASCII
-f, --force don't complain, do it
-i, --input <file> input file name
-v, --verbose be more verbose (show symbol address, etc)

[1]: https://lore.kernel.org/linux-perf-users/htq5vhx6piet4nuq2mmhk7fs2bhfykv52dbppwxmo3s7du2odf@styd27tioc6e/

Fixes: 230a7a71f92212e7 ("libsubcmd: Fix parse-options memory leak")
Suggested-by: Namhyung Kim <[e-mail]>
Signed-off-by: Aditya Gupta <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Athira Rajeev <[e-mail]>
Cc: Disha Goel <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kajol Jain <[e-mail]>
Cc: Madhavan Srinivasan <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/subcmd/parse-options.c

···
 			const char *const subcommands[], const char *usagestr[], int flags)
 {
 	struct parse_opt_ctx_t ctx;
-	char *buf = NULL;
 
 	/* build usage string if it's not provided */
 	if (subcommands && !usagestr[0]) {
+		char *buf = NULL;
+
 		astrcatf(&buf, "%s %s [<options>] {", subcmd_config.exec_name, argv[0]);
 
 		for (int i = 0; subcommands[i]; i++) {
···
 			astrcatf(&error_buf, "unknown switch `%c'", *ctx.opt);
 		usage_with_options(usagestr, options);
 	}
-	if (buf) {
-		usagestr[0] = NULL;
-		free(buf);
-	}
+
 	return parse_options_end(&ctx);
 }
 

tools/perf/builtin-kmem.c

···
 
 out_delete:
 	perf_session__delete(session);
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)kmem_usage[0]);
 
 	return ret;
 }

tools/perf/builtin-kvm.c

···
 	else
 		usage_with_options(kvm_usage, kvm_options);
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)kvm_usage[0]);
+
 	return 0;
 }

tools/perf/builtin-kwork.c

···
 	} else
 		usage_with_options(kwork_usage, kwork_options);
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)kwork_usage[0]);
+
 	return 0;
 }

tools/perf/builtin-lock.c

···
 		usage_with_options(lock_usage, lock_options);
 	}
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)lock_usage[0]);
+
 	zfree(&lockhash_table);
 	return rc;
 }

tools/perf/builtin-mem.c

···
 	else
 		usage_with_options(mem_usage, mem_options);
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)mem_usage[0]);
+
 	return 0;
 }

tools/perf/builtin-sched.c

···
 		usage_with_options(sched_usage, sched_options);
 	}
 
+	/* free usage string allocated by parse_options_subcommand */
+	free((void *)sched_usage[0]);
+
 	return 0;
 }