tracing/timerlat: Move hrtimer_init to timerlat_fd open()

JIRA: https://issues.redhat.com/browse/RHEL-28655

commit 1389358bb008e7625942846e9f03554319b7fecc
Author: Daniel Bristot de Oliveira <bristot@kernel.org>
Date:   Thu Feb 1 16:13:39 2024 +0100

tracing/timerlat: Move hrtimer_init to timerlat_fd open()

	tracing/timerlat: Move hrtimer_init to timerlat_fd open()

	Currently, the timerlat's hrtimer is initialized at the first read of
	timerlat_fd, and destroyed at close(). It works, but it causes an error
	if the user program open() and close() the file without reading.

	Here's an example:

	 # echo NO_OSNOISE_WORKLOAD > /sys/kernel/debug/tracing/osnoise/options
	 # echo timerlat > /sys/kernel/debug/tracing/current_tracer

	 # cat <<EOF > ./timerlat_load.py
	 # !/usr/bin/env python3

	 timerlat_fd = open("/sys/kernel/tracing/osnoise/per_cpu/cpu0/timerlat_fd", 'r')
	 timerlat_fd.close();
	 EOF

	 # ./taskset -c 0 ./timerlat_load.py
	<BOOM>

	 BUG: kernel NULL pointer dereference, address: 0000000000000010
	 #PF: supervisor read access in kernel mode
	 #PF: error_code(0x0000) - not-present page
	 PGD 0 P4D 0
	 Oops: 0000 [#1] PREEMPT SMP NOPTI
	 CPU: 1 PID: 2673 Comm: python3 Not tainted 6.6.13-200.fc39.x86_64 #1
	 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-1.fc39 04/01/2014
	 RIP: 0010:hrtimer_active+0xd/0x50
	 Code: 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 48 8b 57 30 <8b> 42 10 a8 01 74 09 f3 90 8b 42 10 a8 01 75 f7 80 7f 38 00 75 1d
	 RSP: 0018:ffffb031009b7e10 EFLAGS: 00010286
	 RAX: 000000000002db00 RBX: ffff9118f786db08 RCX: 0000000000000000
	 RDX: 0000000000000000 RSI: ffff9117a0e64400 RDI: ffff9118f786db08
	 RBP: ffff9118f786db80 R08: ffff9117a0ddd420 R09: ffff9117804d4f70
	 R10: 0000000000000000 R11: 0000000000000000 R12: ffff9118f786db08
	 R13: ffff91178fdd5e20 R14: ffff9117840978c0 R15: 0000000000000000
	 FS:  00007f2ffbab1740(0000) GS:ffff9118f7840000(0000) knlGS:0000000000000000
	 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
	 CR2: 0000000000000010 CR3: 00000001b402e000 CR4: 0000000000750ee0
	 PKRU: 55555554
	 Call Trace:
	  <TASK>
	  ? __die+0x23/0x70
	  ? page_fault_oops+0x171/0x4e0
	  ? srso_alias_return_thunk+0x5/0x7f
	  ? avc_has_extended_perms+0x237/0x520
	  ? exc_page_fault+0x7f/0x180
	  ? asm_exc_page_fault+0x26/0x30
	  ? hrtimer_active+0xd/0x50
	  hrtimer_cancel+0x15/0x40
	  timerlat_fd_release+0x48/0xe0
	  __fput+0xf5/0x290
	  __x64_sys_close+0x3d/0x80
	  do_syscall_64+0x60/0x90
	  ? srso_alias_return_thunk+0x5/0x7f
	  ? __x64_sys_ioctl+0x72/0xd0
	  ? srso_alias_return_thunk+0x5/0x7f
	  ? syscall_exit_to_user_mode+0x2b/0x40
	  ? srso_alias_return_thunk+0x5/0x7f
	  ? do_syscall_64+0x6c/0x90
	  ? srso_alias_return_thunk+0x5/0x7f
	  ? exit_to_user_mode_prepare+0x142/0x1f0
	  ? srso_alias_return_thunk+0x5/0x7f
	  ? syscall_exit_to_user_mode+0x2b/0x40
	  ? srso_alias_return_thunk+0x5/0x7f
	  ? do_syscall_64+0x6c/0x90
	  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
	 RIP: 0033:0x7f2ffb321594
	 Code: 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 80 3d d5 cd 0d 00 00 74 13 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 3c c3 0f 1f 00 55 48 89 e5 48 83 ec 10 89 7d
	 RSP: 002b:00007ffe8d8eef18 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
	 RAX: ffffffffffffffda RBX: 00007f2ffba4e668 RCX: 00007f2ffb321594
	 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
	 RBP: 00007ffe8d8eef40 R08: 0000000000000000 R09: 0000000000000000
	 R10: 55c926e3167eae79 R11: 0000000000000202 R12: 0000000000000003
	 R13: 00007ffe8d8ef030 R14: 0000000000000000 R15: 00007f2ffba4e668
	  </TASK>
	 CR2: 0000000000000010
	 ---[ end trace 0000000000000000 ]---

	Move hrtimer_init to timerlat_fd open() to avoid this problem.

	Link: https://lore.kernel.org/linux-trace-kernel/7324dd3fc0035658c99b825204a66049389c56e3.1706798888.git.bristot@kernel.org

	Cc: Masami Hiramatsu <mhiramat@kernel.org>
	Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	Cc: stable@vger.kernel.org
	Fixes: e88ed227f639 ("tracing/timerlat: Add user-space interface")
	Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
	Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Signed-off-by: John Kacur <jkacur@redhat.com>

kernel/trace/trace_osnoise.c

@@ -2444,6 +2444,9 @@ static int timerlat_fd_open(struct inode *inode, struct file *file)
 	tlat = this_cpu_tmr_var();
 	tlat->count = 0;
 
+	hrtimer_init(&tlat->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
+	tlat->timer.function = timerlat_irq;
+
 	migrate_enable();
 	return 0;
 };
@@ -2526,9 +2529,6 @@ timerlat_fd_read(struct file *file, char __user *ubuf, size_t count,
 		tlat->tracing_thread = false;
 		tlat->kthread = current;
 
-		hrtimer_init(&tlat->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
-		tlat->timer.function = timerlat_irq;
-
 		/* Annotate now to drift new period */
 		tlat->abs_period = hrtimer_cb_get_time(&tlat->timer);