From: Tejun Heo <tj@kernel.org> mainline inclusion from mainline-v6.12-rc1 commit 7bb6f0810ecfb73a9d7a2ca56fb001e0201a6758 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/IDC9YK Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commi... -------------------------------- BPF schedulers might not want to schedule certain tasks - e.g. kernel threads. This patch adds p->scx.disallow which can be set by BPF schedulers in such cases. The field can be changed anytime and setting it in ops.prep_enable() guarantees that the task can never be scheduled by sched_ext. scx_qmap is updated with the -d option to disallow a specific PID: # echo $$ 1092 # grep -E '(policy)|(ext\.enabled)' /proc/self/sched policy : 0 ext.enabled : 0 # ./set-scx 1092 # grep -E '(policy)|(ext\.enabled)' /proc/self/sched policy : 7 ext.enabled : 0 Run "scx_qmap -p -d 1092" in another terminal. # cat /sys/kernel/sched_ext/nr_rejected 1 # grep -E '(policy)|(ext\.enabled)' /proc/self/sched policy : 0 ext.enabled : 0 # ./set-scx 1092 setparam failed for 1092 (Permission denied) - v4: Refreshed on top of tip:sched/core. - v3: Update description to reflect /sys/kernel/sched_ext interface change. - v2: Use atomic_long_t instead of atomic64_t for scx_kick_cpus_pnt_seqs to accommodate 32bit archs. Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Barret Rhoden <brho@google.com> Reviewed-by: David Vernet <dvernet@meta.com> Acked-by: Josh Don <joshdon@google.com> Acked-by: Hao Luo <haoluo@google.com> Acked-by: Barret Rhoden <brho@google.com> Signed-off-by: Zicheng Qu <quzicheng@huawei.com> --- include/linux/sched/ext.h | 12 ++++++++ kernel/sched/ext.c | 50 ++++++++++++++++++++++++++++++++++ kernel/sched/ext.h | 2 ++ kernel/sched/syscalls.c | 4 +++ tools/sched_ext/scx_qmap.bpf.c | 4 +++ tools/sched_ext/scx_qmap.c | 11 ++++++-- 6 files changed, 81 insertions(+), 2 deletions(-) diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h index 96031252436f..ea7c501ac819 100644 --- a/include/linux/sched/ext.h +++ b/include/linux/sched/ext.h @@ -137,6 +137,18 @@ struct sched_ext_entity { */ u64 slice; + /* + * If set, reject future sched_setscheduler(2) calls updating the policy + * to %SCHED_EXT with -%EACCES. + * + * If set from ops.init_task() and the task's policy is already + * %SCHED_EXT, which can happen while the BPF scheduler is being loaded + * or by inhering the parent's policy during fork, the task's policy is + * rejected and forcefully reverted to %SCHED_NORMAL. The number of + * such events are reported through /sys/kernel/debug/sched_ext::nr_rejected. + */ + bool disallow; /* reject switching into SCX */ + /* cold fields */ /* must be the last field, see init_scx_entity() */ struct list_head tasks_node; diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index baeb66505472..e4eea4c56513 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -487,6 +487,8 @@ struct static_key_false scx_has_op[SCX_OPI_END] = static atomic_t scx_exit_kind = ATOMIC_INIT(SCX_EXIT_DONE); static struct scx_exit_info *scx_exit_info; +static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0); + /* * The maximum amount of time in jiffies that a task may be runnable without * being scheduled on a CPU. If this timeout is exceeded, it will trigger @@ -2337,6 +2339,8 @@ static int scx_ops_init_task(struct task_struct *p, struct task_group *tg, bool { int ret; + p->scx.disallow = false; + if (SCX_HAS_OP(init_task)) { struct scx_init_task_args args = { .fork = fork, @@ -2351,6 +2355,27 @@ static int scx_ops_init_task(struct task_struct *p, struct task_group *tg, bool scx_set_task_state(p, SCX_TASK_INIT); + if (p->scx.disallow) { + struct rq *rq; + struct rq_flags rf; + + rq = task_rq_lock(p, &rf); + + /* + * We're either in fork or load path and @p->policy will be + * applied right after. Reverting @p->policy here and rejecting + * %SCHED_EXT transitions from scx_check_setscheduler() + * guarantees that if ops.init_task() sets @p->disallow, @p can + * never be in SCX. + */ + if (p->policy == SCHED_EXT) { + p->policy = SCHED_NORMAL; + atomic_long_inc(&scx_nr_rejected); + } + + task_rq_unlock(rq, p, &rf); + } + p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT; return 0; } @@ -2554,6 +2579,18 @@ static void switched_from_scx(struct rq *rq, struct task_struct *p) static void wakeup_preempt_scx(struct rq *rq, struct task_struct *p,int wake_flags) {} static void switched_to_scx(struct rq *rq, struct task_struct *p) {} +int scx_check_setscheduler(struct task_struct *p, int policy) +{ + lockdep_assert_rq_held(task_rq(p)); + + /* if disallow, reject transitioning into SCX */ + if (scx_enabled() && READ_ONCE(p->scx.disallow) && + p->policy != policy && policy == SCHED_EXT) + return -EACCES; + + return 0; +} + /* * Omitted operations: * @@ -2708,9 +2745,17 @@ static ssize_t scx_attr_switch_all_show(struct kobject *kobj, } SCX_ATTR(switch_all); +static ssize_t scx_attr_nr_rejected_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_nr_rejected)); +} +SCX_ATTR(nr_rejected); + static struct attribute *scx_global_attrs[] = { &scx_attr_state.attr, &scx_attr_switch_all.attr, + &scx_attr_nr_rejected.attr, NULL, }; @@ -3183,6 +3228,8 @@ static int scx_ops_enable(struct sched_ext_ops *ops) atomic_set(&scx_exit_kind, SCX_EXIT_NONE); scx_warned_zero_slice = false; + atomic_long_set(&scx_nr_rejected, 0); + /* * Keep CPUs stable during enable so that the BPF scheduler can track * online CPUs by watching ->on/offline_cpu() after ->init(). @@ -3481,6 +3528,9 @@ static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log, if (off >= offsetof(struct task_struct, scx.slice) && off + size <= offsetofend(struct task_struct, scx.slice)) return SCALAR_VALUE; + if (off >= offsetof(struct task_struct, scx.disallow) && + off + size <= offsetofend(struct task_struct, scx.disallow)) + return SCALAR_VALUE; } return -EACCES; diff --git a/kernel/sched/ext.h b/kernel/sched/ext.h index 56fcdb0b2c05..33a9f7fe5832 100644 --- a/kernel/sched/ext.h +++ b/kernel/sched/ext.h @@ -35,6 +35,7 @@ void scx_pre_fork(struct task_struct *p); int scx_fork(struct task_struct *p); void scx_post_fork(struct task_struct *p); void scx_cancel_fork(struct task_struct *p); +int scx_check_setscheduler(struct task_struct *p, int policy); bool task_should_scx(struct task_struct *p); void init_sched_ext_class(void); @@ -72,6 +73,7 @@ static inline void scx_pre_fork(struct task_struct *p) {} static inline int scx_fork(struct task_struct *p) { return 0; } static inline void scx_post_fork(struct task_struct *p) {} static inline void scx_cancel_fork(struct task_struct *p) {} +static inline int scx_check_setscheduler(struct task_struct *p, int policy) { return 0; } static inline bool task_on_scx(const struct task_struct *p) { return false; } static inline void init_sched_ext_class(void) {} diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index 76e9f70f3287..396fb2518c79 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -695,6 +695,10 @@ int __sched_setscheduler(struct task_struct *p, goto unlock; } + retval = scx_check_setscheduler(p, policy); + if (retval) + goto unlock; + /* * If not changing anything there's no need to proceed further, * but store a possible modification of reset_on_fork. diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c index 8beae08dfdc7..5ff217c4bfa0 100644 --- a/tools/sched_ext/scx_qmap.bpf.c +++ b/tools/sched_ext/scx_qmap.bpf.c @@ -32,6 +32,7 @@ const volatile u64 slice_ns = SCX_SLICE_DFL; const volatile u32 stall_user_nth; const volatile u32 stall_kernel_nth; const volatile u32 dsp_batch; +const volatile s32 disallow_tgid; u32 test_error_cnt; @@ -243,6 +244,9 @@ void BPF_STRUCT_OPS(qmap_dispatch, s32 cpu, struct task_struct *prev) s32 BPF_STRUCT_OPS(qmap_init_task, struct task_struct *p, struct scx_init_task_args *args) { + if (p->tgid == disallow_tgid) + p->scx.disallow = true; + /* * @p is new. Let's ensure that its task_ctx is available. We can sleep * in this function and the following will automatically use GFP_KERNEL. diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c index 6e9e9726cd62..a2614994cfaa 100644 --- a/tools/sched_ext/scx_qmap.c +++ b/tools/sched_ext/scx_qmap.c @@ -19,13 +19,15 @@ const char help_fmt[] = "\n" "See the top-level comment in .bpf.c for more details.\n" "\n" -"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-b COUNT] [-p] [-v]\n" +"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-b COUNT]\n" +" [-d PID] [-p] [-v]\n" "\n" " -s SLICE_US Override slice duration\n" " -e COUNT Trigger scx_bpf_error() after COUNT enqueues\n" " -t COUNT Stall every COUNT'th user thread\n" " -T COUNT Stall every COUNT'th kernel thread\n" " -b COUNT Dispatch upto COUNT tasks together\n" +" -d PID Disallow a process from switching into SCHED_EXT (-1 for self)\n" " -p Switch only tasks on SCHED_EXT policy intead of all\n" " -v Print libbpf debug messages\n" " -h Display this help and exit\n"; @@ -57,7 +59,7 @@ int main(int argc, char **argv) skel = SCX_OPS_OPEN(qmap_ops, scx_qmap); - while ((opt = getopt(argc, argv, "s:e:t:T:b:pvh")) != -1) { + while ((opt = getopt(argc, argv, "s:e:t:T:b:d:pvh")) != -1) { switch (opt) { case 's': skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000; @@ -74,6 +76,11 @@ int main(int argc, char **argv) case 'b': skel->rodata->dsp_batch = strtoul(optarg, NULL, 0); break; + case 'd': + skel->rodata->disallow_tgid = strtol(optarg, NULL, 0); + if (skel->rodata->disallow_tgid < 0) + skel->rodata->disallow_tgid = getpid(); + break; case 'p': skel->struct_ops.qmap_ops->flags |= SCX_OPS_SWITCH_PARTIAL; break; -- 2.34.1