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rcu-tasks: Fix access non-existent percpu rtpcp variable in rcu_tasks…
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…_need_gpcb()

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
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.

[ neeraj.upadhyay: Fix htmldocs build error reported by Stephen Rothwell ]

Closes: https://lore.kernel.org/linux-input/CALMA0xaTSMN+p4xUXkzrtR5r6k7hgoswcaXx7baR_z9r5jjskw@mail.gmail.com/T/#u
Reported-by: Zhixu Liu <[email protected]>
Signed-off-by: Zqiang <[email protected]>
Signed-off-by: Neeraj Upadhyay <[email protected]>
  • Loading branch information
Zqiang authored and Neeraj Upadhyay committed Aug 14, 2024
1 parent 7945b74 commit fd70e9f
Showing 1 changed file with 53 additions and 29 deletions.
82 changes: 53 additions & 29 deletions kernel/rcu/tasks.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
* @rtp_blkd_tasks: List of tasks blocked as readers.
* @rtp_exit_list: List of tasks in the latter portion of do_exit().
* @cpu: CPU number corresponding to this entry.
* @index: Index of this CPU in rtpcp_array of the rcu_tasks structure.
* @rtpp: Pointer to the rcu_tasks structure.
*/
struct rcu_tasks_percpu {
Expand All @@ -49,6 +50,7 @@ struct rcu_tasks_percpu {
struct list_head rtp_blkd_tasks;
struct list_head rtp_exit_list;
int cpu;
int index;
struct rcu_tasks *rtpp;
};

Expand Down Expand Up @@ -76,6 +78,7 @@ struct rcu_tasks_percpu {
* @call_func: This flavor's call_rcu()-equivalent function.
* @wait_state: Task state for synchronous grace-period waits (default TASK_UNINTERRUPTIBLE).
* @rtpcpu: This flavor's rcu_tasks_percpu structure.
* @rtpcp_array: Array of pointers to rcu_tasks_percpu structure of CPUs in cpu_possible_mask.
* @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks.
* @percpu_enqueue_lim: Number of per-CPU callback queues in use for enqueuing.
* @percpu_dequeue_lim: Number of per-CPU callback queues in use for dequeuing.
Expand Down Expand Up @@ -110,6 +113,7 @@ 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;
Expand Down Expand Up @@ -182,6 +186,8 @@ 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
Expand Down Expand Up @@ -245,6 +251,8 @@ 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;
Expand All @@ -254,14 +262,9 @@ 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);

Expand All @@ -273,14 +276,29 @@ 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.
Expand Down Expand Up @@ -348,7 +366,7 @@ 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.
Expand All @@ -368,10 +386,10 @@ 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);
Expand Down Expand Up @@ -444,6 +462,8 @@ 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. */
Expand Down Expand Up @@ -481,7 +501,7 @@ 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;
Expand All @@ -496,7 +516,9 @@ 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));
Expand All @@ -511,30 +533,32 @@ 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));
Expand Down

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