On 11/22/22 4:56 PM, Martin KaFai Lau wrote:
On 11/22/22 11:53 AM, Yonghong Song wrote:
+SEC("?fentry.s/" SYS_PREFIX "sys_nanosleep")
+int task_acquire(void *ctx)
+{
+ struct task_struct *task, *real_parent;
+
+ task = bpf_get_current_task_btf();
+ bpf_rcu_read_lock();
+ real_parent = task->real_parent;
+ /* acquire a reference which can be used outside rcu read lock
region */
+ real_parent = bpf_task_acquire(real_parent);
Does the bpf_task_acquire() kfunc need a change to do
refcount_inc_not_zero() and KF_RET_NULL?
We have this definition in kernel:
BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
So the argument is trusted args so, either marked as
PTR_TRUSTED/MEM_ALLOC or have a reference acquired already, so
I guess we should be fine here.
Also, some more 'skip' checks in prog_tests/rcu_read_lock.c is needed
for gcc. This is failing in gcc CI:
https://github.com/kernel-patches/bpf/actions/runs/3527747280/jobs/5917628248#step:6:5624
; bpf_rcu_read_lock();
2: (85) call bpf_rcu_read_lock#26650
; real_parent = task->real_parent;
3: (79) r1 = *(u64 *)(r6 +1416) ;
R1_w=ptr_task_struct(off=0,imm=0) R6_w=trusted_ptr_task_struct(off=0,imm=0)
; real_parent = bpf_task_acquire(real_parent);
4: (85) call bpf_task_acquire#26666
R1 must be referenced or trusted
processed 5 insns (limit 1000000) max_states_per_insn 0 total_states
0 peak_states 0 mark_read 0
-- END PROG LOAD LOG --
libbpf: prog 'task_acquire': failed to load: -22
Yes, we should skip this for gcc compiled kernel since rcu tag is not
available.
+ bpf_rcu_read_unlock();
+ (void)bpf_task_storage_get(&map_a, real_parent, 0, 0);
+ bpf_task_release(real_parent);
+ return 0;
+}
+
+SEC("?fentry.s/" SYS_PREFIX "sys_nanosleep")
+int no_lock(void *ctx)
+{
+ struct task_struct *task, *real_parent;
+
+ /* no bpf_rcu_read_lock(), old code still works */
+ task = bpf_get_current_task_btf();
+ real_parent = task->real_parent;
+ bpf_printk("pid %u\n", real_parent->pid);
nit. Can bpf_printk be avoided here?
I could add a target_pid comparison to prevent the issue. But
will follow your suggestion to use a different function instead
of bpf_printk.
Others lgtm.
