[PATCH 5/5] io_uring: add IORING_OP_WAITID support

Jens Axboe
2023-08-02T23:15:32Z

This adds support for an async version of waitid(2), in a fully async
version. If an event isn't immediately available, wait for a callback
to trigger a retry.

The format of the sqe is as follows:

sqe->len The 'which', the idtype being queried/waited for.
sqe->fd The 'pid' (or id) being waited for.
sqe->file_index The 'options' being set.
sqe->addr2 A pointer to siginfo_t, if any, being filled in.

buf_index, add3, and waitid_flags are reserved/unused for now.
waitid_flags will be used for options for this request type. One
interesting use case may be to add multi-shot support, so that the
request stays armed and posts a notification every time a monitored
process state change occurs.

Note that this does not support rusage, on Arnd's recommendation.

See the waitid(2) man page for details on the arguments.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
include/linux/io_uring_types.h | 2 +
include/uapi/linux/io_uring.h | 2 +
io_uring/Makefile | 2 +-
io_uring/cancel.c | 5 +
io_uring/io_uring.c | 3 +
io_uring/opdef.c | 9 +
io_uring/waitid.c | 313 +++++++++++++++++++++++++++++++++
io_uring/waitid.h | 15 ++
8 files changed, 350 insertions(+), 1 deletion(-)
create mode 100644 io_uring/waitid.c
create mode 100644 io_uring/waitid.h

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index a7f03d8d879f..598553877fc2 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -276,6 +276,8 @@ struct io_ring_ctx {
struct hlist_head futex_list;
struct io_alloc_cache futex_cache;

+ struct hlist_head waitid_list;
+
const struct cred *sq_creds; /* cred used for __io_sq_thread() */
struct io_sq_data *sq_data; /* if using sq thread polling */

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 420f38675769..8fca2cffc343 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -66,6 +66,7 @@ struct io_uring_sqe {
__u32 msg_ring_flags;
__u32 uring_cmd_flags;
__u32 futex_flags;
+ __u32 waitid_flags;
};
__u64 user_data; /* data to be passed back at completion time */
/* pack this to avoid bogus arm OABI complaints */
@@ -239,6 +240,7 @@ enum io_uring_op {
IORING_OP_FUTEX_WAIT,
IORING_OP_FUTEX_WAKE,
IORING_OP_FUTEX_WAITV,
+ IORING_OP_WAITID,

/* this goes last, obviously */
IORING_OP_LAST,
diff --git a/io_uring/Makefile b/io_uring/Makefile
index 2e4779bc550c..e5be47e4fc3b 100644
--- a/io_uring/Makefile
+++ b/io_uring/Makefile
@@ -8,6 +8,6 @@ obj-$(CONFIG_IO_URING) += io_uring.o xattr.o nop.o fs.o splice.o \
statx.o net.o msg_ring.o timeout.o \
sqpoll.o fdinfo.o tctx.o poll.o \
cancel.o kbuf.o rsrc.o rw.o opdef.o \
- notif.o
+ notif.o waitid.o
obj-$(CONFIG_IO_WQ) += io-wq.o
obj-$(CONFIG_FUTEX) += futex.o
diff --git a/io_uring/cancel.c b/io_uring/cancel.c
index 3dba8ccb1cd8..a01f3f41012b 100644
--- a/io_uring/cancel.c
+++ b/io_uring/cancel.c
@@ -16,6 +16,7 @@
#include "poll.h"
#include "timeout.h"
#include "futex.h"
+#include "waitid.h"
#include "cancel.h"

struct io_cancel {
@@ -124,6 +125,10 @@ int io_try_cancel(struct io_uring_task *tctx, struct io_cancel_data *cd,
if (ret != -ENOENT)
return ret;

+ ret = io_waitid_cancel(ctx, cd, issue_flags);
+ if (ret != -ENOENT)
+ return ret;
+
spin_lock(&ctx->completion_lock);
if (!(cd->flags & IORING_ASYNC_CANCEL_FD))
ret = io_timeout_cancel(ctx, cd);
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index e52cbdcb29b8..94147e0835bf 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -93,6 +93,7 @@
#include "net.h"
#include "notif.h"
#include "futex.h"
+#include "waitid.h"

#include "timeout.h"
#include "poll.h"
@@ -352,6 +353,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
ctx->submit_state.free_list.next = NULL;
INIT_WQ_LIST(&ctx->locked_free_list);
INIT_HLIST_HEAD(&ctx->futex_list);
+ INIT_HLIST_HEAD(&ctx->waitid_list);
INIT_DELAYED_WORK(&ctx->fallback_work, io_fallback_req_func);
INIT_WQ_LIST(&ctx->submit_state.compl_reqs);
return ctx;
@@ -3286,6 +3288,7 @@ static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
mutex_lock(&ctx->uring_lock);
ret |= io_poll_remove_all(ctx, task, cancel_all);
ret |= io_futex_remove_all(ctx, task, cancel_all);
+ ret |= io_waitid_remove_all(ctx, task, cancel_all);
mutex_unlock(&ctx->uring_lock);
ret |= io_kill_timeouts(ctx, task, cancel_all);
if (task)
diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index b9e1e12cac9c..1c5cfa9d7b31 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -34,6 +34,7 @@
#include "cancel.h"
#include "rw.h"
#include "futex.h"
+#include "waitid.h"

static int io_no_issue(struct io_kiocb *req, unsigned int issue_flags)
{
@@ -453,6 +454,10 @@ const struct io_issue_def io_issue_defs[] = {
.prep = io_eopnotsupp_prep,
#endif
},
+ [IORING_OP_WAITID] = {
+ .prep = io_waitid_prep,
+ .issue = io_waitid,
+ },
};

const struct io_cold_def io_cold_defs[] = {
@@ -681,6 +686,10 @@ const struct io_cold_def io_cold_defs[] = {
[IORING_OP_FUTEX_WAITV] = {
.name = "FUTEX_WAITV",
},
+ [IORING_OP_WAITID] = {
+ .name = "WAITID",
+ .async_size = sizeof(struct io_waitid_async),
+ },
};

const char *io_uring_get_opcode(u8 opcode)
diff --git a/io_uring/waitid.c b/io_uring/waitid.c
new file mode 100644
index 000000000000..14ffa07e161a
--- /dev/null
+++ b/io_uring/waitid.c
@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Support for async notification of waitid
+ */
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/compat.h>
+#include <linux/io_uring.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "io_uring.h"
+#include "cancel.h"
+#include "waitid.h"
+#include "../kernel/exit.h"
+
+struct io_waitid {
+ struct file *file;
+ int which;
+ pid_t upid;
+ int options;
+ struct wait_queue_head *head;
+ struct siginfo __user *infop;
+ struct waitid_info info;
+};
+
+static void io_waitid_free(struct io_kiocb *req)
+{
+ struct io_waitid_async *iwa = req->async_data;
+
+ put_pid(iwa->wo.wo_pid);
+ kfree(req->async_data);
+ req->async_data = NULL;
+ req->flags &= ~REQ_F_ASYNC_DATA;
+}
+
+#ifdef CONFIG_COMPAT
+static bool io_waitid_compat_copy_si(struct io_waitid *iw, int signo)
+{
+ struct compat_siginfo __user *infop;
+ bool ret;
+
+ infop = (struct compat_siginfo __user *) iw->infop;
+
+ if (!user_write_access_begin(infop, sizeof(*infop)))
+ return false;
+
+ unsafe_put_user(signo, &infop->si_signo, Efault);
+ unsafe_put_user(0, &infop->si_errno, Efault);
+ unsafe_put_user(iw->info.cause, &infop->si_code, Efault);
+ unsafe_put_user(iw->info.pid, &infop->si_pid, Efault);
+ unsafe_put_user(iw->info.uid, &infop->si_uid, Efault);
+ unsafe_put_user(iw->info.status, &infop->si_status, Efault);
+ ret = true;
+done:
+ user_write_access_end();
+ return ret;
+Efault:
+ ret = false;
+ goto done;
+}
+#endif
+
+static bool io_waitid_copy_si(struct io_kiocb *req, int signo)
+{
+ struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
+ bool ret;
+
+ if (!iw->infop)
+ return true;
+
+#ifdef CONFIG_COMPAT
+ if (req->ctx->compat)
+ return io_waitid_compat_copy_si(iw, signo);
+#endif
+
+ if (!user_write_access_begin(iw->infop, sizeof(*iw->infop)))
+ return false;
+
+ unsafe_put_user(signo, &iw->infop->si_signo, Efault);
+ unsafe_put_user(0, &iw->infop->si_errno, Efault);
+ unsafe_put_user(iw->info.cause, &iw->infop->si_code, Efault);
+ unsafe_put_user(iw->info.pid, &iw->infop->si_pid, Efault);
+ unsafe_put_user(iw->info.uid, &iw->infop->si_uid, Efault);
+ unsafe_put_user(iw->info.status, &iw->infop->si_status, Efault);
+ ret = true;
+done:
+ user_write_access_end();
+ return ret;
+Efault:
+ ret = false;
+ goto done;
+}
+
+static int io_waitid_finish(struct io_kiocb *req, int ret)
+{
+ int signo = 0;
+
+ if (ret > 0) {
+ signo = SIGCHLD;
+ ret = 0;
+ }
+
+ if (!io_waitid_copy_si(req, signo))
+ ret = -EFAULT;
+ io_waitid_free(req);
+ return ret;
+}
+
+static void io_waitid_complete(struct io_kiocb *req, int ret)
+{
+ struct io_tw_state ts = { .locked = true };
+
+ lockdep_assert_held(&req->ctx->uring_lock);
+
+ /*
+ * Did cancel find it meanwhile?
+ */
+ if (hlist_unhashed(&req->hash_node))
+ return;
+
+ hlist_del_init(&req->hash_node);
+
+ ret = io_waitid_finish(req, ret);
+ if (ret < 0)
+ req_set_fail(req);
+ io_req_set_res(req, ret, 0);
+ io_req_task_complete(req, &ts);
+}
+
+static bool __io_waitid_cancel(struct io_ring_ctx *ctx, struct io_kiocb *req)
+{
+ struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
+ struct wait_queue_head *head;
+
+ head = READ_ONCE(iw->head);
+ if (head) {
+ struct io_waitid_async *iwa = req->async_data;
+
+ spin_lock_irq(&head->lock);
+ list_del_init(&iwa->wo.child_wait.entry);
+ iw->head = NULL;
+ spin_unlock_irq(&head->lock);
+ io_waitid_complete(req, -ECANCELED);
+ return true;
+ }
+
+ return false;
+}
+
+int io_waitid_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
+ unsigned int issue_flags)
+{
+ struct hlist_node *tmp;
+ struct io_kiocb *req;
+ int nr = 0;
+
+ if (cd->flags & (IORING_ASYNC_CANCEL_FD|IORING_ASYNC_CANCEL_FD_FIXED))
+ return -ENOENT;
+
+ io_ring_submit_lock(ctx, issue_flags);
+ hlist_for_each_entry_safe(req, tmp, &ctx->waitid_list, hash_node) {
+ if (req->cqe.user_data != cd->data &&
+ !(cd->flags & IORING_ASYNC_CANCEL_ANY))
+ continue;
+ if (__io_waitid_cancel(ctx, req))
+ nr++;
+ if (!(cd->flags & IORING_ASYNC_CANCEL_ALL))
+ break;
+ }
+ io_ring_submit_unlock(ctx, issue_flags);
+
+ if (nr)
+ return nr;
+
+ return -ENOENT;
+}
+
+bool io_waitid_remove_all(struct io_ring_ctx *ctx, struct task_struct *task,
+ bool cancel_all)
+{
+ struct hlist_node *tmp;
+ struct io_kiocb *req;
+ bool found = false;
+
+ lockdep_assert_held(&ctx->uring_lock);
+
+ hlist_for_each_entry_safe(req, tmp, &ctx->waitid_list, hash_node) {
+ if (!io_match_task_safe(req, task, cancel_all))
+ continue;
+ __io_waitid_cancel(ctx, req);
+ found = true;
+ }
+
+ return found;
+}
+
+static void io_waitid_cb(struct io_kiocb *req, struct io_tw_state *ts)
+{
+ struct io_waitid_async *iwa = req->async_data;
+ struct io_ring_ctx *ctx = req->ctx;
+ int ret;
+
+ /*
+ * If we get -ERESTARTSYS here, we need to re-arm and check again
+ * to ensure we get another callback. If the retry works, then we can
+ * just remove ourselves from the waitqueue again and finish the
+ * request.
+ */
+ ret = __do_wait(&iwa->wo);
+ if (unlikely(ret == -ERESTARTSYS)) {
+ struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
+
+ io_tw_lock(ctx, ts);
+ iw->head = &current->signal->wait_chldexit;
+ add_wait_queue(iw->head, &iwa->wo.child_wait);
+ ret = __do_wait(&iwa->wo);
+ if (ret == -ERESTARTSYS)
+ return;
+
+ remove_wait_queue(iw->head, &iwa->wo.child_wait);
+ iw->head = NULL;
+ }
+
+ io_tw_lock(ctx, ts);
+ io_waitid_complete(req, ret);
+}
+
+static int io_waitid_wait(struct wait_queue_entry *wait, unsigned mode,
+ int sync, void *key)
+{
+ struct wait_opts *wo = container_of(wait, struct wait_opts, child_wait);
+ struct io_waitid_async *iwa = container_of(wo, struct io_waitid_async, wo);
+ struct io_kiocb *req = iwa->req;
+ struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
+ struct task_struct *p = key;
+
+ if (!pid_child_should_wake(wo, p))
+ return 0;
+
+ req->io_task_work.func = io_waitid_cb;
+ io_req_task_work_add(req);
+ iw->head = NULL;
+ list_del_init(&wait->entry);
+ return 1;
+}
+
+int io_waitid_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+ struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
+
+ if (sqe->addr || sqe->buf_index || sqe->addr3 || sqe->waitid_flags)
+ return -EINVAL;
+
+ iw->which = READ_ONCE(sqe->len);
+ iw->options = READ_ONCE(sqe->file_index);
+ iw->upid = READ_ONCE(sqe->fd);
+ iw->infop = u64_to_user_ptr(READ_ONCE(sqe->addr2));
+ iw->head = NULL;
+ return 0;
+}
+
+int io_waitid(struct io_kiocb *req, unsigned int issue_flags)
+{
+ struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
+ struct io_ring_ctx *ctx = req->ctx;
+ struct io_waitid_async *iwa;
+ unsigned int f_flags = 0;
+ int ret;
+
+ if (io_alloc_async_data(req))
+ return -ENOMEM;
+
+ iwa = req->async_data;
+ iwa->req = req;
+
+ ret = kernel_waitid_prepare(&iwa->wo, iw->which, iw->upid, &iw->info,
+ iw->options, NULL, &f_flags);
+ if (ret)
+ goto done;
+
+ /*
+ * Arm our callback and add us to the waitqueue, in case no events
+ * are available.
+ */
+ init_waitqueue_func_entry(&iwa->wo.child_wait, io_waitid_wait);
+ iwa->wo.child_wait.private = req->task;
+ iw->head = &current->signal->wait_chldexit;
+ add_wait_queue(iw->head, &iwa->wo.child_wait);
+
+ io_ring_submit_lock(ctx, issue_flags);
+ hlist_add_head(&req->hash_node, &ctx->waitid_list);
+
+ ret = __do_wait(&iwa->wo);
+ if (ret == -ERESTARTSYS) {
+ io_ring_submit_unlock(ctx, issue_flags);
+ return IOU_ISSUE_SKIP_COMPLETE;
+ }
+
+ hlist_del_init(&req->hash_node);
+ remove_wait_queue(iw->head, &iwa->wo.child_wait);
+ iw->head = NULL;
+ ret = io_waitid_finish(req, ret);
+
+ io_ring_submit_unlock(ctx, issue_flags);
+done:
+ if (ret < 0)
+ req_set_fail(req);
+ io_req_set_res(req, ret, 0);
+ return IOU_OK;
+}
diff --git a/io_uring/waitid.h b/io_uring/waitid.h
new file mode 100644
index 000000000000..956a8adafe8c
--- /dev/null
+++ b/io_uring/waitid.h
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "../kernel/exit.h"
+
+struct io_waitid_async {
+ struct io_kiocb *req;
+ struct wait_opts wo;
+};
+
+int io_waitid_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_waitid(struct io_kiocb *req, unsigned int issue_flags);
+int io_waitid_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
+ unsigned int issue_flags);
+bool io_waitid_remove_all(struct io_ring_ctx *ctx, struct task_struct *task,
+ bool cancel_all);
--
2.40.1