tracing: Fix memory leak in tracing_read_pipe()

kmemleak reports this issue:

unreferenced object 0xffff888105a18900 (size 128):
  comm "test_progs", pid 18933, jiffies 4336275356 (age 22801.766s)
  hex dump (first 32 bytes):
    25 73 00 90 81 88 ff ff 26 05 00 00 42 01 58 04  %s......&...B.X.
    03 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<00000000560143a1>] __kmalloc_node_track_caller+0x4a/0x140
    [<000000006af00822>] krealloc+0x8d/0xf0
    [<00000000c309be6a>] trace_iter_expand_format+0x99/0x150
    [<000000005a53bdb6>] trace_check_vprintf+0x1e0/0x11d0
    [<0000000065629d9d>] trace_event_printf+0xb6/0xf0
    [<000000009a690dc7>] trace_raw_output_bpf_trace_printk+0x89/0xc0
    [<00000000d22db172>] print_trace_line+0x73c/0x1480
    [<00000000cdba76ba>] tracing_read_pipe+0x45c/0x9f0
    [<0000000015b58459>] vfs_read+0x17b/0x7c0
    [<000000004aeee8ed>] ksys_read+0xed/0x1c0
    [<0000000063d3d898>] do_syscall_64+0x3b/0x90
    [<00000000a06dda7f>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

iter->fmt alloced in
  tracing_read_pipe() -> .. ->trace_iter_expand_format(), but not
freed, to fix, add free in tracing_release_pipe()

Link: https://lkml.kernel.org/r/1667819090-4643-1-git-send-email-wangyufen@huawei.com

Cc: stable@vger.kernel.org
Fixes: efbbdaa2 ("tracing: Show real address for trace event arguments")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Wang Yufen <wangyufen@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -6657,6 +6657,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
 	mutex_unlock(&trace_types_lock);
 
 	free_cpumask_var(iter->started);
+	kfree(iter->fmt);
 	mutex_destroy(&iter->mutex);
 	kfree(iter);