bpf: Revert "bpf: remove unnecessary rcu_read_{lock,unlock}() in multi-uprobe attach logic"

JIRA: https://issues.redhat.com/browse/RHEL-96605

commit 4e2e684
Author: Di Shen <di.shen@unisoc.com>
Date:   Tue May 20 13:49:43 2025 +0800

    bpf: Revert "bpf: remove unnecessary rcu_read_{lock,unlock}() in multi-uprobe attach logic"
    
    This reverts commit 4a8f635.
    
    Althought get_pid_task() internally already calls rcu_read_lock() and
    rcu_read_unlock(), the find_vpid() was not.
    
    The documentation for find_vpid() clearly states:
    "Must be called with the tasklist_lock or rcu_read_lock() held."
    
    Add proper rcu_read_lock/unlock() to protect the find_vpid().
    
    Fixes: 4a8f635 ("bpf: remove unnecessary rcu_read_{lock,unlock}() in multi-uprobe attach logic")
    Reported-by: Xuewen Yan <xuewen.yan@unisoc.com>
    Signed-off-by: Di Shen <di.shen@unisoc.com>
    Acked-by: Andrii Nakryiko <andrii@kernel.org>
    Link: https://lore.kernel.org/r/20250520054943.5002-1-xuewen.yan@unisoc.com
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Signed-off-by: Felix Maurer <fmaurer@redhat.com>

Author: fmaurer-rh

kernel/trace/bpf_trace.c

@@ -3404,7 +3404,9 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	}
 
 	if (pid) {
+		rcu_read_lock();
 		task = get_pid_task(find_vpid(pid), PIDTYPE_TGID);
+		rcu_read_unlock();
 		if (!task) {
 			err = -ESRCH;
 			goto error_path_put;