> > For kernels built with CONFIG_FORCE_NR_CPUS=y, the nr_cpu_ids is > defined as NR_CPUS instead of the number of possible cpus, this > will cause the following system panic: > > smpboot: Allowing 4 CPUs, 0 hotplug CPUs > ... > setup_percpu: NR_CPUS:512 nr_cpumask_bits:512 nr_cpu_ids:512 nr_node_ids:1 > ... > BUG: unable to handle page fault for address: ffffffff9911c8c8 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > Oops: 0000 [#1] PREEMPT SMP PTI > CPU: 0 PID: 15 Comm: rcu_tasks_trace Tainted: G W > 6.6.21 #1 5dc7acf91a5e8e9ac9dcfc35bee0245691283ea6 > RIP: 0010:rcu_tasks_need_gpcb+0x25d/0x2c0 > RSP: 0018:ffffa371c00a3e60 EFLAGS: 00010082 > CR2: ffffffff9911c8c8 CR3: 000000040fa20005 CR4: 00000000001706f0 > Call Trace: > <TASK> > ? __die+0x23/0x80 > ? page_fault_oops+0xa4/0x180 > ? exc_page_fault+0x152/0x180 > ? asm_exc_page_fault+0x26/0x40 > ? rcu_tasks_need_gpcb+0x25d/0x2c0 > ? __pfx_rcu_tasks_kthread+0x40/0x40 > rcu_tasks_one_gp+0x69/0x180 > rcu_tasks_kthread+0x94/0xc0 > kthread+0xe8/0x140 > ? __pfx_kthread+0x40/0x40 > ret_from_fork+0x34/0x80 > ? __pfx_kthread+0x40/0x40 > ret_from_fork_asm+0x1b/0x80 > </TASK> > > Considering that there may be holes in the CPU numbers, use the > maximum possible cpu number, instead of nr_cpu_ids, for configuring > enqueue and dequeue limits. > > Closes: https://lore.kernel.org/linux-input/CALMA0xaTSMN+p4xUXkzrtR5r6k7hgoswcaXx7baR_z9r5jjskw@xxxxxxxxxxxxxx/T/#u > Reported-by: Zhixu Liu <zhixu.liu@xxxxxxxxx> > Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx> > --- > kernel/rcu/tasks.h | 80 +++++++++++++++++++++++++++++----------------- > 1 file changed, 51 insertions(+), 29 deletions(-) > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h > index 2b1d6abf3ba3..12d63ce84cc9 100644 > --- a/kernel/rcu/tasks.h > +++ b/kernel/rcu/tasks.h > @@ -49,6 +49,7 @@ struct rcu_tasks_percpu { > struct list_head rtp_blkd_tasks; > struct list_head rtp_exit_list; > int cpu; > + int index; > struct rcu_tasks *rtpp; > }; > > @@ -110,6 +111,7 @@ struct rcu_tasks { > call_rcu_func_t call_func; > unsigned int wait_state; > struct rcu_tasks_percpu __percpu *rtpcpu; > + struct rcu_tasks_percpu **rtpcp_array; > int percpu_enqueue_shift; > int percpu_enqueue_lim; > int percpu_dequeue_lim; > @@ -182,6 +184,8 @@ module_param(rcu_task_collapse_lim, int, 0444); > static int rcu_task_lazy_lim __read_mostly = 32; > module_param(rcu_task_lazy_lim, int, 0444); > > +static int rcu_task_cpu_ids; > + > /* RCU tasks grace-period state for debugging. */ > #define RTGS_INIT 0 > #define RTGS_WAIT_WAIT_CBS 1 > @@ -245,6 +249,8 @@ static void cblist_init_generic(struct rcu_tasks *rtp) > int cpu; > int lim; > int shift; > + int maxcpu; > + int index = 0; > > if (rcu_task_enqueue_lim < 0) { > rcu_task_enqueue_lim = 1; > @@ -254,14 +260,9 @@ static void cblist_init_generic(struct rcu_tasks *rtp) > } > lim = rcu_task_enqueue_lim; > > - if (lim > nr_cpu_ids) > - lim = nr_cpu_ids; > - shift = ilog2(nr_cpu_ids / lim); > - if (((nr_cpu_ids - 1) >> shift) >= lim) > - shift++; > - WRITE_ONCE(rtp->percpu_enqueue_shift, shift); > - WRITE_ONCE(rtp->percpu_dequeue_lim, lim); > - smp_store_release(&rtp->percpu_enqueue_lim, lim); > + rtp->rtpcp_array = kcalloc(num_possible_cpus(), sizeof(struct rcu_tasks_percpu *), GFP_KERNEL); > + BUG_ON(!rtp->rtpcp_array); > + > for_each_possible_cpu(cpu) { > struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); > > @@ -273,14 +274,29 @@ static void cblist_init_generic(struct rcu_tasks *rtp) > INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq); > rtpcp->cpu = cpu; > rtpcp->rtpp = rtp; > + rtpcp->index = index; > + rtp->rtpcp_array[index] = rtpcp; > + index++; > if (!rtpcp->rtp_blkd_tasks.next) > INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks); > if (!rtpcp->rtp_exit_list.next) > INIT_LIST_HEAD(&rtpcp->rtp_exit_list); > + maxcpu = cpu; > } > > - pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d.\n", rtp->name, > - data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim), rcu_task_cb_adjust); > + rcu_task_cpu_ids = maxcpu + 1; > + if (lim > rcu_task_cpu_ids) > + lim = rcu_task_cpu_ids; > + shift = ilog2(rcu_task_cpu_ids / lim); > + if (((rcu_task_cpu_ids - 1) >> shift) >= lim) > + shift++; > + WRITE_ONCE(rtp->percpu_enqueue_shift, shift); > + WRITE_ONCE(rtp->percpu_dequeue_lim, lim); > + smp_store_release(&rtp->percpu_enqueue_lim, lim); It seems that smp_store_release does not need, the WRITE_ONCE(rtp->percpu_enqueue_lim, lim) is enough, cblist_init_generic() is invoke in early boot, at this time, no other tasks access these percpu_*lim. Thanks Zqiang > + > + pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d rcu_task_cpu_ids=%d.\n", > + rtp->name, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim), > + rcu_task_cb_adjust, rcu_task_cpu_ids); > } > > // Compute wakeup time for lazy callback timer. > @@ -348,7 +364,7 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, > rtpcp->rtp_n_lock_retries = 0; > } > if (rcu_task_cb_adjust && ++rtpcp->rtp_n_lock_retries > rcu_task_contend_lim && > - READ_ONCE(rtp->percpu_enqueue_lim) != nr_cpu_ids) > + READ_ONCE(rtp->percpu_enqueue_lim) != rcu_task_cpu_ids) > needadjust = true; // Defer adjustment to avoid deadlock. > } > // Queuing callbacks before initialization not yet supported. > @@ -368,10 +384,10 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, > raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); > if (unlikely(needadjust)) { > raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); > - if (rtp->percpu_enqueue_lim != nr_cpu_ids) { > + if (rtp->percpu_enqueue_lim != rcu_task_cpu_ids) { > WRITE_ONCE(rtp->percpu_enqueue_shift, 0); > - WRITE_ONCE(rtp->percpu_dequeue_lim, nr_cpu_ids); > - smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids); > + WRITE_ONCE(rtp->percpu_dequeue_lim, rcu_task_cpu_ids); > + smp_store_release(&rtp->percpu_enqueue_lim, rcu_task_cpu_ids); > pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name); > } > raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); > @@ -444,6 +460,8 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp) > > dequeue_limit = smp_load_acquire(&rtp->percpu_dequeue_lim); > for (cpu = 0; cpu < dequeue_limit; cpu++) { > + if (!cpu_possible(cpu)) > + continue; > struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); > > /* Advance and accelerate any new callbacks. */ > @@ -481,7 +499,7 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp) > if (rcu_task_cb_adjust && ncbs <= rcu_task_collapse_lim) { > raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); > if (rtp->percpu_enqueue_lim > 1) { > - WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(nr_cpu_ids)); > + WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(rcu_task_cpu_ids)); > smp_store_release(&rtp->percpu_enqueue_lim, 1); > rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu(); > gpdone = false; > @@ -496,7 +514,9 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp) > pr_info("Completing switch %s to CPU-0 callback queuing.\n", rtp->name); > } > if (rtp->percpu_dequeue_lim == 1) { > - for (cpu = rtp->percpu_dequeue_lim; cpu < nr_cpu_ids; cpu++) { > + for (cpu = rtp->percpu_dequeue_lim; cpu < rcu_task_cpu_ids; cpu++) { > + if (!cpu_possible(cpu)) > + continue; > struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); > > WARN_ON_ONCE(rcu_segcblist_n_cbs(&rtpcp->cblist)); > @@ -511,30 +531,32 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp) > // Advance callbacks and invoke any that are ready. > static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu *rtpcp) > { > - int cpu; > - int cpunext; > int cpuwq; > unsigned long flags; > int len; > + int index; > struct rcu_head *rhp; > struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); > struct rcu_tasks_percpu *rtpcp_next; > > - cpu = rtpcp->cpu; > - cpunext = cpu * 2 + 1; > - if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { > - rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); > - cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND; > - queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); > - cpunext++; > - if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { > - rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); > - cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND; > + index = rtpcp->index * 2 + 1; > + if (index < num_possible_cpus()) { > + rtpcp_next = rtp->rtpcp_array[index]; > + if (rtpcp_next->cpu < smp_load_acquire(&rtp->percpu_dequeue_lim)) { > + cpuwq = rcu_cpu_beenfullyonline(rtpcp_next->cpu) ? rtpcp_next->cpu : WORK_CPU_UNBOUND; > queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); > + index++; > + if (index < num_possible_cpus()) { > + rtpcp_next = rtp->rtpcp_array[index]; > + if (rtpcp_next->cpu < smp_load_acquire(&rtp->percpu_dequeue_lim)) { > + cpuwq = rcu_cpu_beenfullyonline(rtpcp_next->cpu) ? rtpcp_next->cpu : WORK_CPU_UNBOUND; > + queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); > + } > + } > } > } > > - if (rcu_segcblist_empty(&rtpcp->cblist) || !cpu_possible(cpu)) > + if (rcu_segcblist_empty(&rtpcp->cblist)) > return; > raw_spin_lock_irqsave_rcu_node(rtpcp, flags); > rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq)); > -- > 2.17.1 >
