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Enqueueing is atomic > with no spinlock and can happen in any context. > > Include a unit test for basic functionality - runs a boot/module-load > time. Does not use kunit framework. > > Signed-off-by: NeilBrown > --- > include/linux/sunrpc/svc_lwq.h | 79 +++++++++++++++++++ I'm wondering what your longer-term intentions are for this new mechanism. If it is only useful for SunRPC, then perhaps this header belongs under net/sunrpc instead. > net/sunrpc/Kconfig | 6 ++ > net/sunrpc/Makefile | 2 +- > net/sunrpc/svc_lwq.c | 135 +++++++++++++++++++++++++++++++++ > 4 files changed, 221 insertions(+), 1 deletion(-) > create mode 100644 include/linux/sunrpc/svc_lwq.h > create mode 100644 net/sunrpc/svc_lwq.c > > diff --git a/include/linux/sunrpc/svc_lwq.h b/include/linux/sunrpc/svc_lwq.h > new file mode 100644 > index 000000000000..4bd6cbffa155 > --- /dev/null > +++ b/include/linux/sunrpc/svc_lwq.h > @@ -0,0 +1,79 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > + > +#ifndef SUNRPC_SVC_LWQ_H > +#define SUNRPC_SVC_LWQ_H > + > +/* > + * light-weight single linked queue > + * > + * Entries can be enqueued from any context with no locking. > + * Entries can be dequeued from process context with integrated locking. > + * > + */ > +#include > +#include > +#include > + > +struct lwq_node { > + struct llist_node node; > +}; > + > +struct lwq { > + spinlock_t lock; > + struct llist_node *ready; /* entries to be dequeued */ > + struct llist_head new; /* entries being enqueued */ > +}; > + > +static inline void lwq_init(struct lwq *q) > +{ > + spin_lock_init(&q->lock); > + q->ready = NULL; > + init_llist_head(&q->new); > +} > + > +static inline bool lwq_empty(struct lwq *q) > +{ > + return READ_ONCE(q->ready) == NULL && llist_empty(&q->new); > +} > + > +struct llist_node *__lwq_dequeue(struct lwq *q); > +#define lwq_dequeue(_q, _type, _member) \ > + ({ struct llist_node *_n = __lwq_dequeue(_q); \ > + _n ? container_of(_n, _type, _member.node) : NULL; }) > + > +struct llist_node *lwq_dequeue_all(struct lwq *q); > + > +/** > + * lwq_for_each_safe: iterate over detached queue allowing deletion > + * @_n: iterator variable > + * @_t1: temporary struct llist_node ** > + * @_t2: temporary struct llist_node * > + * @_l: address of llist_node pointer from lwq_dequeue_all() > + * @_member: member in _n where lwq_node is found. > + * > + * Iterate over members in a dequeued list. If the iterator variable > + * is set to NULL, the iterator removes that entry from the queue. > + */ > +#define lwq_for_each_safe(_n, _t1, _t2, _l, _member) \ > + for (_t1 = (_l); \ > + *(_t1) ? (_n = container_of(*(_t1), typeof(*(_n)), _member.node),\ > + _t2 = ((*_t1)->next), \ > + true) \ > + : false; \ > + (_n) ? (_t1 = &(_n)->_member.node.next, 0) \ > + : ((*(_t1) = (_t2)), 0)) > + > +static inline bool lwq_enqueue(struct lwq_node *n, struct lwq *q) > +{ > + return llist_add(&n->node, &q->new) && READ_ONCE(q->ready) == NULL; > +} > + > +static inline bool lwq_enqueue_batch(struct llist_node *n, struct lwq *q) > +{ > + struct llist_node *e = n; > + > + return llist_add_batch(llist_reverse_order(n), e, &q->new) && > + READ_ONCE(q->ready) == NULL; > +} > + > +#endif /* SUNRPC_SVC_LWQ_H */ > diff --git a/net/sunrpc/Kconfig b/net/sunrpc/Kconfig > index 2d8b67dac7b5..5de87d005962 100644 > --- a/net/sunrpc/Kconfig > +++ b/net/sunrpc/Kconfig > @@ -115,3 +115,9 @@ config SUNRPC_XPRT_RDMA > > If unsure, or you know there is no RDMA capability on your > hardware platform, say N. > + > +config SUNRPC_LWQ_TEST > + bool "RPC: enable boot-time test for lwq queuing" > + depends on SUNRPC > + help > + Enable boot-time test of lwq functionality. > diff --git a/net/sunrpc/Makefile b/net/sunrpc/Makefile > index f89c10fe7e6a..b224cba1d0da 100644 > --- a/net/sunrpc/Makefile > +++ b/net/sunrpc/Makefile > @@ -10,7 +10,7 @@ obj-$(CONFIG_SUNRPC_XPRT_RDMA) += xprtrdma/ > > sunrpc-y := clnt.o xprt.o socklib.o xprtsock.o sched.o \ > auth.o auth_null.o auth_tls.o auth_unix.o \ > - svc.o svcsock.o svcauth.o svcauth_unix.o \ > + svc.o svc_lwq.o svcsock.o svcauth.o svcauth_unix.o \ > addr.o rpcb_clnt.o timer.o xdr.o \ > sunrpc_syms.o cache.o rpc_pipe.o sysfs.o \ > svc_xprt.o \ > diff --git a/net/sunrpc/svc_lwq.c b/net/sunrpc/svc_lwq.c > new file mode 100644 > index 000000000000..528ad7e3abb1 > --- /dev/null > +++ b/net/sunrpc/svc_lwq.c > @@ -0,0 +1,135 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Light weight single-linked queue. > + * > + * Entries are enqueued to the head of an llist, with no blocking. > + * This can happen in any context. > + * > + * Entries are dequeued using a spinlock to protect against > + * multiple access. The llist is staged in reverse order, and refreshed > + * from the llist when it exhausts. > + */ > +#include > +#include > + > +struct llist_node *__lwq_dequeue(struct lwq *q) > +{ > + struct llist_node *this; > + > + if (lwq_empty(q)) > + return NULL; > + spin_lock(&q->lock); > + this = q->ready; > + if (!this) > + this = llist_reverse_order(llist_del_all(&q->new)); > + if (this) > + q->ready = llist_next(this); > + spin_unlock(&q->lock); > + return this; > +} > + > +struct llist_node *lwq_dequeue_all(struct lwq *q) > +{ > + struct llist_node *r, *t, **ep; > + > + if (lwq_empty(q)) > + return NULL; > + > + spin_lock(&q->lock); > + r = q->ready; > + q->ready = NULL; > + t = llist_del_all(&q->new); > + spin_unlock(&q->lock); > + ep = &r; > + while (*ep) > + ep = &(*ep)->next; > + *ep = llist_reverse_order(t); > + return r; > +} > + > +#if IS_ENABLED(CONFIG_SUNRPC_LWQ_TEST) > + > +#include > +#include > +#include > +#include > +#include > +struct tnode { > + struct lwq_node n; > + int i; > + int c; > +}; > + > +static int lwq_exercise(void *qv) > +{ > + struct lwq *q = qv; > + int cnt; > + struct tnode *t; > + > + for (cnt = 0; cnt < 10000; cnt++) { > + wait_var_event(q, (t = lwq_dequeue(q, struct tnode, n)) != NULL); > + t->c++; > + if (lwq_enqueue(&t->n, q)) > + wake_up_var(q); > + } > + wait_var_event(q, kthread_should_stop()); > + return 0; > +} > + > +static int lwq_test(void) > +{ > + int i; > + struct lwq q; > + struct llist_node *l, **t1, *t2; > + struct tnode *t; > + struct task_struct *threads[8]; > + > + printk(KERN_INFO "testing lwq....\n"); > + lwq_init(&q); > + printk(KERN_INFO " lwq: run some threads\n"); > + for (i = 0; i < ARRAY_SIZE(threads); i++) > + threads[i] = kthread_run(lwq_exercise, &q, "lwq_test-%d", i); > + for (i = 0; i < 100; i++) { > + t = kmalloc(sizeof(*t), GFP_KERNEL); > + t->i = i; > + t->c = 0; > + if (lwq_enqueue(&t->n, &q)) > + wake_up_var(&q); > + }; > + /* wait for threads to exit */ > + for (i = 0; i < ARRAY_SIZE(threads); i++) > + if (!IS_ERR_OR_NULL(threads[i])) > + kthread_stop(threads[i]); > + printk(KERN_INFO " lwq: dequeue first 50:"); > + for (i = 0; i < 50 ; i++) { > + if (i && (i % 10) == 0) { > + printk(KERN_CONT "\n"); > + printk(KERN_INFO " lwq: ... "); > + } > + t = lwq_dequeue(&q, struct tnode, n); > + printk(KERN_CONT " %d(%d)", t->i, t->c); > + kfree(t); > + } > + printk(KERN_CONT "\n"); > + l = lwq_dequeue_all(&q); > + printk(KERN_INFO " lwq: delete the multiples of 3 (test lwq_for_each_safe())\n"); > + lwq_for_each_safe(t, t1, t2, &l, n) { > + if ((t->i % 3) == 0) { > + t->i = -1; > + kfree(t); > + t = NULL; > + } > + } > + if (l) > + lwq_enqueue_batch(l, &q); > + printk(KERN_INFO " lwq: dequeue remaining:"); > + while ((t = lwq_dequeue(&q, struct tnode, n)) != NULL) { > + printk(KERN_CONT " %d", t->i); > + kfree(t); > + } > + printk(KERN_CONT "\n"); > + return 0; > +} > + > +module_init(lwq_test); > +#endif /* CONFIG_SUNRPC_LWQ_TEST*/ > -- > 2.40.1 > -- Chuck Lever