[PATCH v3] rcu-tasks: Fix access non-existent percpu rtpcp variable in rcu_tasks_need_gpcb()

From: Zqiang
Date: Wed Jul 10 2024 - 00:46:02 EST

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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);
+
+ 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

Next message: Umang Jain: "[PATCH 0/2] media: imx335: Support vertical flip"
Previous message: Barry Song: "Re: [PATCH v7] mm: shrink skip folio mapped by an exiting process"
Next in thread: Z qiang: "Re: [PATCH v3] rcu-tasks: Fix access non-existent percpu rtpcp variable in rcu_tasks_need_gpcb()"
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