From a9e3760b0838299649c0d57cca44daaf40ba3c33 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 14 Sep 2026 22:12:34 -1000 Subject: sched_ext: Maintain an online cid mask in the scheduler arena Schedulers on the default cid mapping treat [0, nr_online_cids) as the online set and restart on hotplug. Schedulers that install their own mapping with scx_bpf_cid_override() have no way to learn which cids are online: the count no longer identifies members and the CPU-form cpumask is unusable from cid programs. This is an obvious hole in the cid API. Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's arena, allocated alongside the per-CPU scratch masks and populated after the cid mapping is finalized and before ops.init(), for child schedulers too. The pointer stays valid through ops.exit() with no reference to take. It is the arena offset as a void pointer, the same form struct_ops arena arguments arrive in. The verifier types the void return as a scalar for the program's arena cast. The mask follows the SCX hotplug notifications: seeded from cpu_active_mask and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask only inside a hotplug transition. Updates walk the scheduler list under the lock that also serializes unlinking. Reads are live, not atomic snapshots. Root initialization excludes hotplug. v2: Reworded the getter kerneldoc (Andrea Righi). Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- samples/kfifo/bytestream-example.c | 196 +++++++++++++++++++++++++++++++++++++ 1 file changed, 196 insertions(+) create mode 100644 samples/kfifo/bytestream-example.c (limited to 'samples/kfifo/bytestream-example.c') diff --git a/samples/kfifo/bytestream-example.c b/samples/kfifo/bytestream-example.c new file mode 100644 index 000000000..4ae29a12c --- /dev/null +++ b/samples/kfifo/bytestream-example.c @@ -0,0 +1,196 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Sample kfifo byte stream implementation + * + * Copyright (C) 2010 Stefani Seibold + */ + +#include +#include +#include +#include +#include + +/* + * This module shows how to create a byte stream fifo. + */ + +/* fifo size in elements (bytes) */ +#define FIFO_SIZE 32 + +/* name of the proc entry */ +#define PROC_FIFO "bytestream-fifo" + +/* lock for procfs read access */ +static DEFINE_MUTEX(read_access); + +/* lock for procfs write access */ +static DEFINE_MUTEX(write_access); + +/* + * define DYNAMIC in this example for a dynamically allocated fifo. + * + * Otherwise the fifo storage will be a part of the fifo structure. + */ +#if 0 +#define DYNAMIC +#endif + +#ifdef DYNAMIC +static struct kfifo test; +#else +static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE); +#endif + +static const unsigned char expected_result[FIFO_SIZE] = { + 3, 4, 5, 6, 7, 8, 9, 0, + 1, 20, 21, 22, 23, 24, 25, 26, + 27, 28, 29, 30, 31, 32, 33, 34, + 35, 36, 37, 38, 39, 40, 41, 42, +}; + +static int __init testfunc(void) +{ + unsigned char buf[6]; + unsigned char i, j; + unsigned int ret; + + printk(KERN_INFO "byte stream fifo test start\n"); + + /* put string into the fifo */ + kfifo_in(&test, "hello", 5); + + /* put values into the fifo */ + for (i = 0; i != 10; i++) + kfifo_put(&test, i); + + /* show the number of used elements */ + printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test)); + + /* get max of 5 bytes from the fifo */ + i = kfifo_out(&test, buf, 5); + printk(KERN_INFO "buf: %.*s\n", i, buf); + + /* get max of 2 elements from the fifo */ + ret = kfifo_out(&test, buf, 2); + printk(KERN_INFO "ret: %d\n", ret); + /* and put it back to the end of the fifo */ + ret = kfifo_in(&test, buf, ret); + printk(KERN_INFO "ret: %d\n", ret); + + /* skip first element of the fifo */ + printk(KERN_INFO "skip 1st element\n"); + kfifo_skip(&test); + + /* put values into the fifo until is full */ + for (i = 20; kfifo_put(&test, i); i++) + ; + + printk(KERN_INFO "queue len: %u\n", kfifo_len(&test)); + + /* show the first value without removing from the fifo */ + if (kfifo_peek(&test, &i)) + printk(KERN_INFO "%d\n", i); + + /* check the correctness of all values in the fifo */ + j = 0; + while (kfifo_get(&test, &i)) { + printk(KERN_INFO "item = %d\n", i); + if (i != expected_result[j++]) { + printk(KERN_WARNING "value mismatch: test failed\n"); + return -EIO; + } + } + if (j != ARRAY_SIZE(expected_result)) { + printk(KERN_WARNING "size mismatch: test failed\n"); + return -EIO; + } + printk(KERN_INFO "test passed\n"); + + return 0; +} + +static ssize_t fifo_write(struct file *file, const char __user *buf, + size_t count, loff_t *ppos) +{ + int ret; + unsigned int copied; + + if (mutex_lock_interruptible(&write_access)) + return -ERESTARTSYS; + + ret = kfifo_from_user(&test, buf, count, &copied); + + mutex_unlock(&write_access); + if (ret) + return ret; + + return copied; +} + +static ssize_t fifo_read(struct file *file, char __user *buf, + size_t count, loff_t *ppos) +{ + int ret; + unsigned int copied; + + if (mutex_lock_interruptible(&read_access)) + return -ERESTARTSYS; + + ret = kfifo_to_user(&test, buf, count, &copied); + + mutex_unlock(&read_access); + if (ret) + return ret; + + return copied; +} + +static const struct proc_ops fifo_proc_ops = { + .proc_read = fifo_read, + .proc_write = fifo_write, + .proc_lseek = noop_llseek, +}; + +static int __init example_init(void) +{ +#ifdef DYNAMIC + int ret; + + ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL); + if (ret) { + printk(KERN_ERR "error kfifo_alloc\n"); + return ret; + } +#else + INIT_KFIFO(test); +#endif + if (testfunc() < 0) { +#ifdef DYNAMIC + kfifo_free(&test); +#endif + return -EIO; + } + + if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) { +#ifdef DYNAMIC + kfifo_free(&test); +#endif + return -ENOMEM; + } + return 0; +} + +static void __exit example_exit(void) +{ + remove_proc_entry(PROC_FIFO, NULL); +#ifdef DYNAMIC + kfifo_free(&test); +#endif +} + +module_init(example_init); +module_exit(example_exit); +MODULE_DESCRIPTION("Sample kfifo byte stream implementation"); +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Stefani Seibold "); -- cgit v1.3.1