Merge: uprobes: Fix race in uprobe_free_utask

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/7506

JIRA: https://issues.redhat.com/browse/RHEL-120479

Fix kernel panic occurring in perf user callchain code.

The reason for that is the race between `uprobe_free_utask` and bpf profiler code doing the perf user stack unwind and is triggered within `uprobe_free_utask` function:
- after `current->utask` is freed and
- before `current->utask` is set to NULL

See commit message for more details, stack trace, and reproducer.

Signed-off-by: Viktor Malik <vmalik@redhat.com>

Approved-by: Jay Shin <jaeshin@redhat.com>
Approved-by: Gregory Bell <grbell@redhat.com>
Approved-by: Jerome Marchand <jmarchan@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

kernel/events/uprobes.c

@@ -1720,6 +1720,7 @@ void uprobe_free_utask(struct task_struct *t)
 	if (!utask)
 		return;
 
+	t->utask = NULL;
 	if (utask->active_uprobe)
 		put_uprobe(utask->active_uprobe);
 
@@ -1729,7 +1730,6 @@ void uprobe_free_utask(struct task_struct *t)
 
 	xol_free_insn_slot(t);
 	kfree(utask);
-	t->utask = NULL;
 }
 
 /*