On Sun, Feb 4, 2024 at 9:09 AM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
>
> On 2/3/24 7:30 PM, Yafang Shao wrote:
> > 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
> > =============
>
> The error is due to the following in verifier:
>
> } else if (opcode == BPF_EXIT) {
> ...
> if (env->cur_state->active_rcu_lock &&
> !in_rbtree_lock_required_cb(env)) {
> verbose(env, "bpf_rcu_read_unlock is missing\n");
> return -EINVAL;
> }
>
>
> I guess, we could relax the condition not to return -EINVAL if
> it is a static function.
>
> >
> >
> > 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)
>
> __always_inline is also work. But let us improve verifier so we
> can avoid such workarounds in the future. Note that Kumar just
> submitted a patch set to relax spin_lock for static functions:
> https://lore.kernel.org/bpf/20240204120206.796412-1-memxor@xxxxxxxxx/
Agreed, let's improve verifier, but I wouldn't block on it for this
patch set and just use __always_inline for now.
I think we should also work on extending this RCU support to global
functions. We can add per-function annotation (similar to __arg_xxx,
but which will be applied to a function itself), just __rcu or
something like __func_assume_rcu or whatnot, and then there should be
no difference between static and global functions in this regard.
In general, global functions are basically mandatory nowadays for big
production BPF programs (to reduce verification complexity), so we
should strive to keep global functions/subprogs on par with static
subprogs as much as we can.
>
> >
> >>> +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;
> >>> +}
> >>> +
> >> [...]
> >
> >
