On Sat, Feb 3, 2024 at 6:03 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Wed, Jan 31, 2024 at 6:55 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> >
> > Add selftests for the newly added cpumask iter.
> > - cpumask_iter_success
> > - The number of CPUs should be expected when iterating over the cpumask
> > - percpu data extracted from the percpu struct should be expected
> > - It can work in both non-sleepable and sleepable prog
> > - RCU lock is only required by bpf_iter_cpumask_new()
> > - It is fine without calling bpf_iter_cpumask_next()
> >
> > - cpumask_iter_failure
> > - RCU lock is required in sleepable prog
> > - The cpumask to be iterated over can't be NULL
> > - bpf_iter_cpumask_destroy() is required after calling
> > bpf_iter_cpumask_new()
> > - bpf_iter_cpumask_destroy() can only destroy an initilialized iter
> > - bpf_iter_cpumask_next() must use an initilialized iter
>
> typos: initialized
will fix it.
>
> >
> > The result as follows,
> >
> > #64/37 cpumask/test_cpumask_iter:OK
> > #64/38 cpumask/test_cpumask_iter_sleepable:OK
> > #64/39 cpumask/test_cpumask_iter_sleepable:OK
> > #64/40 cpumask/test_cpumask_iter_next_no_rcu:OK
> > #64/41 cpumask/test_cpumask_iter_no_next:OK
> > #64/42 cpumask/test_cpumask_iter:OK
> > #64/43 cpumask/test_cpumask_iter_no_rcu:OK
> > #64/44 cpumask/test_cpumask_iter_no_destroy:OK
> > #64/45 cpumask/test_cpumask_iter_null_pointer:OK
> > #64/46 cpumask/test_cpumask_iter_next_uninit:OK
> > #64/47 cpumask/test_cpumask_iter_destroy_uninit:OK
> > #64 cpumask:OK
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > ---
> > tools/testing/selftests/bpf/config | 1 +
> > .../selftests/bpf/prog_tests/cpumask.c | 152 ++++++++++++++++++
> > .../selftests/bpf/progs/cpumask_common.h | 3 +
> > .../bpf/progs/cpumask_iter_failure.c | 99 ++++++++++++
> > .../bpf/progs/cpumask_iter_success.c | 126 +++++++++++++++
> > 5 files changed, 381 insertions(+)
> > create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_failure.c
> > create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_success.c
> >
>
> LGTM overall, except for seemingly unnecessary use of a big macro
>
> > diff --git a/tools/testing/selftests/bpf/progs/cpumask_common.h b/tools/testing/selftests/bpf/progs/cpumask_common.h
> > index 0cd4aebb97cf..cdb9dc95e9d9 100644
> > --- a/tools/testing/selftests/bpf/progs/cpumask_common.h
> > +++ b/tools/testing/selftests/bpf/progs/cpumask_common.h
> > @@ -55,6 +55,9 @@ void bpf_cpumask_copy(struct bpf_cpumask *dst, const struct cpumask *src) __ksym
> > u32 bpf_cpumask_any_distribute(const struct cpumask *src) __ksym;
> > u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1, const struct cpumask *src2) __ksym;
> > u32 bpf_cpumask_weight(const struct cpumask *cpumask) __ksym;
> > +int bpf_iter_cpumask_new(struct bpf_iter_cpumask *it, const struct cpumask *mask) __ksym;
> > +int *bpf_iter_cpumask_next(struct bpf_iter_cpumask *it) __ksym;
> > +void bpf_iter_cpumask_destroy(struct bpf_iter_cpumask *it) __ksym;
>
> let's mark them __weak so they don't conflict with definitions that
> will eventually come from vmlinux.h (that applies to all the kfunc
> definitions we currently have and we'll need to clean all that up, but
> let's not add non-weak kfuncs going forward)
will change it.
>
> >
> > void bpf_rcu_read_lock(void) __ksym;
> > void bpf_rcu_read_unlock(void) __ksym;
>
> [...]
>
> > diff --git a/tools/testing/selftests/bpf/progs/cpumask_iter_success.c b/tools/testing/selftests/bpf/progs/cpumask_iter_success.c
> > new file mode 100644
> > index 000000000000..4ce14ef98451
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/cpumask_iter_success.c
> > @@ -0,0 +1,126 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/* Copyright (c) 2024 Yafang Shao <laoar.shao@xxxxxxxxx> */
> > +
> > +#include "vmlinux.h"
> > +#include <bpf/bpf_helpers.h>
> > +#include <bpf/bpf_tracing.h>
> > +
> > +#include "task_kfunc_common.h"
> > +#include "cpumask_common.h"
> > +
> > +char _license[] SEC("license") = "GPL";
> > +
> > +extern const struct psi_group_cpu system_group_pcpu __ksym __weak;
> > +extern const struct rq runqueues __ksym __weak;
> > +
> > +int pid;
> > +
> > +#define READ_PERCPU_DATA(meta, cgrp, mask) \
> > +{ \
> > + u32 nr_running = 0, psi_nr_running = 0, nr_cpus = 0; \
> > + struct psi_group_cpu *groupc; \
> > + struct rq *rq; \
> > + int *cpu; \
> > + \
> > + bpf_for_each(cpumask, cpu, mask) { \
> > + rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, *cpu); \
> > + if (!rq) { \
> > + err += 1; \
> > + continue; \
> > + } \
> > + nr_running += rq->nr_running; \
> > + nr_cpus += 1; \
> > + \
> > + groupc = (struct psi_group_cpu *)bpf_per_cpu_ptr(&system_group_pcpu, *cpu); \
> > + if (!groupc) { \
> > + err += 1; \
> > + continue; \
> > + } \
> > + psi_nr_running += groupc->tasks[NR_RUNNING]; \
> > + } \
> > + BPF_SEQ_PRINTF(meta->seq, "nr_running %u nr_cpus %u psi_running %u\n", \
> > + nr_running, nr_cpus, psi_nr_running); \
> > +}
> > +
>
> Does this have to be a gigantic macro? Why can't it be just a function?
It seems that the verifier can't identify a function call between
bpf_rcu_read_lock() and bpf_rcu_read_unlock().
That said, if there's a function call between them, the verifier will fail.
Below is the full verifier log if I define it as :
static inline void read_percpu_data(struct bpf_iter_meta *meta, struct
cgroup *cgrp, const cpumask_t *mask)
VERIFIER LOG:
=============
0: R1=ctx() R10=fp0
; int BPF_PROG(test_cpumask_iter_sleepable, struct bpf_iter_meta
*meta, struct cgroup *cgrp)
0: (b4) w7 = 0 ; R7_w=0
; int BPF_PROG(test_cpumask_iter_sleepable, struct bpf_iter_meta
*meta, struct cgroup *cgrp)
1: (79) r2 = *(u64 *)(r1 +8) ; R1=ctx()
R2_w=trusted_ptr_or_null_cgroup(id=1)
; if (!cgrp)
2: (15) if r2 == 0x0 goto pc+16 ; R2_w=trusted_ptr_cgroup()
; int BPF_PROG(test_cpumask_iter_sleepable, struct bpf_iter_meta
*meta, struct cgroup *cgrp)
3: (79) r6 = *(u64 *)(r1 +0)
func 'bpf_iter_cgroup' arg0 has btf_id 10966 type STRUCT 'bpf_iter_meta'
4: R1=ctx() R6_w=trusted_ptr_bpf_iter_meta()
; bpf_rcu_read_lock();
4: (85) call bpf_rcu_read_lock#84184 ;
; p = bpf_task_from_pid(pid);
5: (18) r1 = 0xffffbc1ad3f72004 ;
R1_w=map_value(map=cpumask_.bss,ks=4,vs=8,off=4)
7: (61) r1 = *(u32 *)(r1 +0) ;
R1_w=scalar(smin=0,smax=umax=0xffffffff,var_off=(0x0; 0xffffffff))
; p = bpf_task_from_pid(pid);
8: (85) call bpf_task_from_pid#84204 ;
R0=ptr_or_null_task_struct(id=3,ref_obj_id=3) refs=3
9: (bf) r8 = r0 ;
R0=ptr_or_null_task_struct(id=3,ref_obj_id=3)
R8_w=ptr_or_null_task_struct(id=3,ref_obj_id=3) refs=3
10: (b4) w7 = 1 ; R7_w=1 refs=3
; if (!p) {
11: (15) if r8 == 0x0 goto pc+6 ;
R8_w=ptr_task_struct(ref_obj_id=3) refs=3
; read_percpu_data(meta, cgrp, p->cpus_ptr);
12: (79) r2 = *(u64 *)(r8 +984) ; R2_w=rcu_ptr_cpumask()
R8_w=ptr_task_struct(ref_obj_id=3) refs=3
; read_percpu_data(meta, cgrp, p->cpus_ptr);
13: (bf) r1 = r6 ;
R1_w=trusted_ptr_bpf_iter_meta() R6=trusted_ptr_bpf_iter_meta() refs=3
14: (85) call pc+6
caller:
R6=trusted_ptr_bpf_iter_meta() R7_w=1
R8_w=ptr_task_struct(ref_obj_id=3) R10=fp0 refs=3
callee:
frame1: R1_w=trusted_ptr_bpf_iter_meta() R2_w=rcu_ptr_cpumask() R10=fp0 refs=3
21: frame1: R1_w=trusted_ptr_bpf_iter_meta() R2_w=rcu_ptr_cpumask()
R10=fp0 refs=3
; static inline void read_percpu_data(struct bpf_iter_meta *meta,
struct cgroup *cgrp, const cpumask_t *mask)
21: (bf) r8 = r1 ; frame1:
R1_w=trusted_ptr_bpf_iter_meta() R8_w=trusted_ptr_bpf_iter_meta()
refs=3
22: (bf) r7 = r10 ; frame1: R7_w=fp0 R10=fp0 refs=3
;
23: (07) r7 += -24 ; frame1: R7_w=fp-24 refs=3
; bpf_for_each(cpumask, cpu, mask) {
24: (bf) r1 = r7 ; frame1: R1_w=fp-24 R7_w=fp-24 refs=3
25: (85) call bpf_iter_cpumask_new#77163 ; frame1: R0=scalar()
fp-24=iter_cpumask(ref_id=4,state=active,depth=0) refs=3,4
; bpf_for_each(cpumask, cpu, mask) {
26: (bf) r1 = r7 ; frame1: R1=fp-24 R7=fp-24 refs=3,4
27: (85) call bpf_iter_cpumask_next#77165 ; frame1: R0_w=0
fp-24=iter_cpumask(ref_id=4,state=drained,depth=0) refs=3,4
28: (bf) r7 = r0 ; frame1: R0_w=0 R7_w=0 refs=3,4
29: (b4) w1 = 0 ; frame1: R1_w=0 refs=3,4
30: (63) *(u32 *)(r10 -40) = r1 ; frame1: R1_w=0 R10=fp0
fp-40=????0 refs=3,4
31: (b4) w1 = 0 ; frame1: R1_w=0 refs=3,4
32: (7b) *(u64 *)(r10 -32) = r1 ; frame1: R1_w=0 R10=fp0
fp-32_w=0 refs=3,4
33: (b4) w9 = 0 ; frame1: R9_w=0 refs=3,4
; bpf_for_each(cpumask, cpu, mask) {
34: (15) if r7 == 0x0 goto pc+57 ; frame1: R7_w=0 refs=3,4
; bpf_for_each(cpumask, cpu, mask) {
92: (bf) r1 = r10 ; frame1: R1_w=fp0 R10=fp0 refs=3,4
; bpf_for_each(cpumask, cpu, mask) {
93: (07) r1 += -24 ; frame1: R1_w=fp-24 refs=3,4
94: (85) call bpf_iter_cpumask_destroy#77161 ; frame1: refs=3
; BPF_SEQ_PRINTF(meta->seq, "nr_running %u nr_cpus %u psi_running %u\n",
95: (61) r1 = *(u32 *)(r10 -40) ; frame1: R1_w=0 R10=fp0
fp-40=????0 refs=3
96: (bc) w1 = w1 ; frame1: R1_w=0 refs=3
97: (7b) *(u64 *)(r10 -8) = r1 ; frame1: R1_w=0 R10=fp0 fp-8_w=0 refs=3
98: (79) r1 = *(u64 *)(r10 -32) ; frame1: R1_w=0 R10=fp0 fp-32=0 refs=3
99: (7b) *(u64 *)(r10 -16) = r1 ; frame1: R1_w=0 R10=fp0 fp-16_w=0 refs=3
100: (7b) *(u64 *)(r10 -24) = r9 ; frame1: R9=0 R10=fp0 fp-24_w=0 refs=3
101: (79) r1 = *(u64 *)(r8 +0) ; frame1:
R1_w=trusted_ptr_seq_file() R8=trusted_ptr_bpf_iter_meta() refs=3
102: (bf) r4 = r10 ; frame1: R4_w=fp0 R10=fp0 refs=3
; bpf_for_each(cpumask, cpu, mask) {
103: (07) r4 += -24 ; frame1: R4_w=fp-24 refs=3
; BPF_SEQ_PRINTF(meta->seq, "nr_running %u nr_cpus %u psi_running %u\n",
104: (18) r2 = 0xffff9bce47e0e210 ; frame1:
R2_w=map_value(map=cpumask_.rodata,ks=4,vs=41) refs=3
106: (b4) w3 = 41 ; frame1: R3_w=41 refs=3
107: (b4) w5 = 24 ; frame1: R5_w=24 refs=3
108: (85) call bpf_seq_printf#126 ; frame1: R0=scalar() refs=3
; }
109: (95) exit
bpf_rcu_read_unlock is missing
processed 45 insns (limit 1000000) max_states_per_insn 0 total_states
5 peak_states 5 mark_read 3
=============
Another workaround is using the __always_inline :
static __always_inline void read_percpu_data(struct bpf_iter_meta
*meta, struct cgroup *cgrp, const cpumask_t *mask)
>
> > +SEC("iter.s/cgroup")
> > +int BPF_PROG(test_cpumask_iter_sleepable, struct bpf_iter_meta *meta, struct cgroup *cgrp)
> > +{
> > + struct task_struct *p;
> > +
> > + /* epilogue */
> > + if (!cgrp)
> > + return 0;
> > +
> > + bpf_rcu_read_lock();
> > + p = bpf_task_from_pid(pid);
> > + if (!p) {
> > + bpf_rcu_read_unlock();
> > + return 1;
> > + }
> > +
> > + READ_PERCPU_DATA(meta, cgrp, p->cpus_ptr);
> > + bpf_task_release(p);
> > + bpf_rcu_read_unlock();
> > + return 0;
> > +}
> > +
>
> [...]
--
Regards
Yafang
