[PATCH] workqueue: Fix race in schedule and flush work

Padmanabha Srinivasaiah
2022-02-10T18:44:32Z

While booting secondary cpus, online cpus mask is transient and can end up
in below calltrace. Using same cpumask for both schedule and flush of
work resolves the issue.

[ 0.377823] CPU3: Booted secondary processor 0x0000000003 [0x410fd083]
[ 0.379040] ------------[ cut here ]------------
[ 0.383662] WARNING: CPU: 0 PID: 10 at kernel/workqueue.c:3084 __flush_work+0x12c/0x138
[ 0.384850] Modules linked in:
[ 0.385403] CPU: 0 PID: 10 Comm: rcu_tasks_rude_ Not tainted 5.17.0-rc3-v8+ #13
[ 0.386473] Hardware name: Raspberry Pi 4 Model B Rev 1.4 (DT)
[ 0.387289] pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 0.388308] pc : __flush_work+0x12c/0x138
[ 0.388970] lr : __flush_work+0x80/0x138
[ 0.389620] sp : ffffffc00aaf3c60
[ 0.390139] x29: ffffffc00aaf3d20 x28: ffffffc009c16af0 x27: ffffff80f761df48
[ 0.391316] x26: 0000000000000004 x25: 0000000000000003 x24: 0000000000000100
[ 0.392493] x23: ffffffffffffffff x22: ffffffc009c16b10 x21: ffffffc009c16b28
[ 0.393668] x20: ffffffc009e53861 x19: ffffff80f77fbf40 x18: 00000000d744fcc9
[ 0.394842] x17: 000000000000000b x16: 00000000000001c2 x15: ffffffc009e57550
[ 0.396016] x14: 0000000000000000 x13: ffffffffffffffff x12: 0000000100000000
[ 0.397190] x11: 0000000000000462 x10: ffffff8040258008 x9 : 0000000100000000
[ 0.398364] x8 : 0000000000000000 x7 : ffffffc0093c8bf4 x6 : 0000000000000000
[ 0.399538] x5 : 0000000000000000 x4 : ffffffc00a976e40 x3 : ffffffc00810444c
[ 0.400711] x2 : 0000000000000004 x1 : 0000000000000000 x0 : 0000000000000000
[ 0.401886] Call trace:
[ 0.402309] __flush_work+0x12c/0x138
[ 0.402941] schedule_on_each_cpu+0x228/0x278
[ 0.403693] rcu_tasks_rude_wait_gp+0x130/0x144
[ 0.404502] rcu_tasks_kthread+0x220/0x254
[ 0.405264] kthread+0x174/0x1ac
[ 0.405837] ret_from_fork+0x10/0x20
[ 0.406456] irq event stamp: 102
[ 0.406966] hardirqs last enabled at (101): [<ffffffc0093c8468>] _raw_spin_unlock_irq+0x78/0xb4
[ 0.408304] hardirqs last disabled at (102): [<ffffffc0093b8270>] el1_dbg+0x24/0x5c
[ 0.409410] softirqs last enabled at (54): [<ffffffc0081b80c8>] local_bh_enable+0xc/0x2c
[ 0.410645] softirqs last disabled at (50): [<ffffffc0081b809c>] local_bh_disable+0xc/0x2c
[ 0.411890] ---[ end trace 0000000000000000 ]---
[ 0.413000] smp: Brought up 1 node, 4 CPUs
[ 0.413762] SMP: Total of 4 processors activated.

Signed-off-by: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
---
kernel/workqueue.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 33f1106b4f99..a3f53f859e9d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3326,28 +3326,38 @@ EXPORT_SYMBOL(cancel_delayed_work_sync);
*/
int schedule_on_each_cpu(work_func_t func)
{
- int cpu;
struct work_struct __percpu *works;
+ cpumask_var_t sched_cpumask;
+ int cpu, ret = 0;

- works = alloc_percpu(struct work_struct);
- if (!works)
+ if (!alloc_cpumask_var(&sched_cpumask, GFP_KERNEL))
return -ENOMEM;

+ works = alloc_percpu(struct work_struct);
+ if (!works) {
+ ret = -ENOMEM;
+ goto free_cpumask;
+ }
+
cpus_read_lock();

- for_each_online_cpu(cpu) {
+ cpumask_copy(sched_cpumask, cpu_online_mask);
+ for_each_cpu_and(cpu, sched_cpumask, cpu_online_mask) {
struct work_struct *work = per_cpu_ptr(works, cpu);

INIT_WORK(work, func);
schedule_work_on(cpu, work);
}

- for_each_online_cpu(cpu)
+ for_each_cpu_and(cpu, sched_cpumask, cpu_online_mask)
flush_work(per_cpu_ptr(works, cpu));

cpus_read_unlock();
free_percpu(works);
- return 0;
+
+free_cpumask:
+ free_cpumask_var(sched_cpumask);
+ return ret;
}

/**
--
2.17.1