Merge tag 'io_uring-5.9-2020-08-15' of git://git.kernel.dk/linux-block

Pull io_uring fixes from Jens Axboe:
"A few differerent things in here.

Seems like syzbot got some more io_uring bits wired up, and we got a
handful of reports and the associated fixes are in here.

General fixes too, and a lot of them marked for stable.

Lastly, a bit of fallout from the async buffered reads, where we now
more easily trigger short reads. Some applications don't really like
that, so the io_read() code now handles short reads internally, and
got a cleanup along the way so that it's now easier to read (and
documented). We're now passing tests that failed before"

* tag 'io_uring-5.9-2020-08-15' of git://git.kernel.dk/linux-block:
io_uring: short circuit -EAGAIN for blocking read attempt
io_uring: sanitize double poll handling
io_uring: internally retry short reads
io_uring: retain iov_iter state over io_read/io_write calls
task_work: only grab task signal lock when needed
io_uring: enable lookup of links holding inflight files
io_uring: fail poll arm on queue proc failure
io_uring: hold 'ctx' reference around task_work queue + execute
fs: RWF_NOWAIT should imply IOCB_NOIO
io_uring: defer file table grabbing request cleanup for locked requests
io_uring: add missing REQ_F_COMP_LOCKED for nested requests
io_uring: fix recursive completion locking on oveflow flush
io_uring: use TWA_SIGNAL for task_work uncondtionally
io_uring: account locked memory before potential error case
io_uring: set ctx sq/cq entry count earlier
io_uring: Fix NULL pointer dereference in loop_rw_iter()
io_uring: add comments on how the async buffered read retry works
io_uring: io_async_buf_func() need not test page bit

fs/io_uring.c

···
 
 struct io_async_rw {
 	struct iovec			fast_iov[UIO_FASTIOV];
-	struct iovec			*iov;
-	ssize_t				nr_segs;
-	ssize_t				size;
+	const struct iovec		*free_iovec;
+	struct iov_iter			iter;
+	size_t				bytes_done;
 	struct wait_page_queue		wpq;
 };
 
···
 static void io_double_put_req(struct io_kiocb *req);
 static void __io_double_put_req(struct io_kiocb *req);
 static struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req);
+static void __io_queue_linked_timeout(struct io_kiocb *req);
 static void io_queue_linked_timeout(struct io_kiocb *req);
 static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 				 struct io_uring_files_update *ip,
···
 static ssize_t io_import_iovec(int rw, struct io_kiocb *req,
 			       struct iovec **iovec, struct iov_iter *iter,
 			       bool needs_lock);
-static int io_setup_async_rw(struct io_kiocb *req, ssize_t io_size,
-			     struct iovec *iovec, struct iovec *fast_iov,
-			     struct iov_iter *iter);
+static int io_setup_async_rw(struct io_kiocb *req, const struct iovec *iovec,
+			     const struct iovec *fast_iov,
+			     struct iov_iter *iter, bool force);
 
 static struct kmem_cache *req_cachep;
 
···
 	}
 }
 
-static void io_req_clean_work(struct io_kiocb *req)
+/*
+ * Returns true if we need to defer file table putting. This can only happen
+ * from the error path with REQ_F_COMP_LOCKED set.
+ */
+static bool io_req_clean_work(struct io_kiocb *req)
 {
 	if (!(req->flags & REQ_F_WORK_INITIALIZED))
-		return;
+		return false;
+
+	req->flags &= ~REQ_F_WORK_INITIALIZED;
 
 	if (req->work.mm) {
 		mmdrop(req->work.mm);
···
 	if (req->work.fs) {
 		struct fs_struct *fs = req->work.fs;
 
+		if (req->flags & REQ_F_COMP_LOCKED)
+			return true;
+
 		spin_lock(&req->work.fs->lock);
 		if (--fs->users)
 			fs = NULL;
···
 			free_fs_struct(fs);
 		req->work.fs = NULL;
 	}
-	req->flags &= ~REQ_F_WORK_INITIALIZED;
+
+	return false;
 }
 
 static void io_prep_async_work(struct io_kiocb *req)
···
 			io_prep_async_work(cur);
 }
 
-static void __io_queue_async_work(struct io_kiocb *req)
+static struct io_kiocb *__io_queue_async_work(struct io_kiocb *req)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	struct io_kiocb *link = io_prep_linked_timeout(req);
···
 	trace_io_uring_queue_async_work(ctx, io_wq_is_hashed(&req->work), req,
 					&req->work, req->flags);
 	io_wq_enqueue(ctx->io_wq, &req->work);
-
-	if (link)
-		io_queue_linked_timeout(link);
+	return link;
 }
 
 static void io_queue_async_work(struct io_kiocb *req)
 {
+	struct io_kiocb *link;
+
 	/* init ->work of the whole link before punting */
 	io_prep_async_link(req);
-	__io_queue_async_work(req);
+	link = __io_queue_async_work(req);
+
+	if (link)
+		io_queue_linked_timeout(link);
 }
 
 static void io_kill_timeout(struct io_kiocb *req)
···
 	do {
 		struct io_defer_entry *de = list_first_entry(&ctx->defer_list,
 						struct io_defer_entry, list);
+		struct io_kiocb *link;
 
 		if (req_need_defer(de->req, de->seq))
 			break;
 		list_del_init(&de->list);
 		/* punt-init is done before queueing for defer */
-		__io_queue_async_work(de->req);
+		link = __io_queue_async_work(de->req);
+		if (link) {
+			__io_queue_linked_timeout(link);
+			/* drop submission reference */
+			link->flags |= REQ_F_COMP_LOCKED;
+			io_put_req(link);
+		}
 		kfree(de);
 	} while (!list_empty(&ctx->defer_list));
 }
···
 		fput(file);
 }
 
-static void io_dismantle_req(struct io_kiocb *req)
+static bool io_dismantle_req(struct io_kiocb *req)
 {
 	io_clean_op(req);
 
···
 		kfree(req->io);
 	if (req->file)
 		io_put_file(req, req->file, (req->flags & REQ_F_FIXED_FILE));
-	io_req_clean_work(req);
 
 	if (req->flags & REQ_F_INFLIGHT) {
 		struct io_ring_ctx *ctx = req->ctx;
···
 			wake_up(&ctx->inflight_wait);
 		spin_unlock_irqrestore(&ctx->inflight_lock, flags);
 	}
+
+	return io_req_clean_work(req);
 }
 
-static void __io_free_req(struct io_kiocb *req)
+static void __io_free_req_finish(struct io_kiocb *req)
 {
-	struct io_ring_ctx *ctx;
+	struct io_ring_ctx *ctx = req->ctx;
 
-	io_dismantle_req(req);
 	__io_put_req_task(req);
-	ctx = req->ctx;
 	if (likely(!io_is_fallback_req(req)))
 		kmem_cache_free(req_cachep, req);
 	else
 		clear_bit_unlock(0, (unsigned long *) &ctx->fallback_req);
 	percpu_ref_put(&ctx->refs);
+}
+
+static void io_req_task_file_table_put(struct callback_head *cb)
+{
+	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
+	struct fs_struct *fs = req->work.fs;
+
+	spin_lock(&req->work.fs->lock);
+	if (--fs->users)
+		fs = NULL;
+	spin_unlock(&req->work.fs->lock);
+	if (fs)
+		free_fs_struct(fs);
+	req->work.fs = NULL;
+	__io_free_req_finish(req);
+}
+
+static void __io_free_req(struct io_kiocb *req)
+{
+	if (!io_dismantle_req(req)) {
+		__io_free_req_finish(req);
+	} else {
+		int ret;
+
+		init_task_work(&req->task_work, io_req_task_file_table_put);
+		ret = task_work_add(req->task, &req->task_work, TWA_RESUME);
+		if (unlikely(ret)) {
+			struct task_struct *tsk;
+
+			tsk = io_wq_get_task(req->ctx->io_wq);
+			task_work_add(tsk, &req->task_work, 0);
+		}
+	}
 }
 
 static bool io_link_cancel_timeout(struct io_kiocb *req)
···
 		return false;
 
 	list_del_init(&link->link_list);
+	link->flags |= REQ_F_COMP_LOCKED;
 	wake_ev = io_link_cancel_timeout(link);
 	req->flags &= ~REQ_F_LINK_TIMEOUT;
 	return wake_ev;
···
 		trace_io_uring_fail_link(req, link);
 
 		io_cqring_fill_event(link, -ECANCELED);
+		link->flags |= REQ_F_COMP_LOCKED;
 		__io_double_put_req(link);
 		req->flags &= ~REQ_F_LINK_TIMEOUT;
 	}
···
 {
 	struct task_struct *tsk = req->task;
 	struct io_ring_ctx *ctx = req->ctx;
-	int ret, notify = TWA_RESUME;
+	int ret, notify;
 
 	/*
-	 * SQPOLL kernel thread doesn't need notification, just a wakeup.
-	 * If we're not using an eventfd, then TWA_RESUME is always fine,
-	 * as we won't have dependencies between request completions for
-	 * other kernel wait conditions.
+	 * SQPOLL kernel thread doesn't need notification, just a wakeup. For
+	 * all other cases, use TWA_SIGNAL unconditionally to ensure we're
+	 * processing task_work. There's no reliable way to tell if TWA_RESUME
+	 * will do the job.
 	 */
-	if (ctx->flags & IORING_SETUP_SQPOLL)
-		notify = 0;
-	else if (ctx->cq_ev_fd)
+	notify = 0;
+	if (!(ctx->flags & IORING_SETUP_SQPOLL))
 		notify = TWA_SIGNAL;
 
 	ret = task_work_add(tsk, cb, notify);
 	if (!ret)
 		wake_up_process(tsk);
+
 	return ret;
 }
 
···
 static void io_req_task_submit(struct callback_head *cb)
 {
 	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
+	struct io_ring_ctx *ctx = req->ctx;
 
 	__io_req_task_submit(req);
+	percpu_ref_put(&ctx->refs);
 }
 
 static void io_req_task_queue(struct io_kiocb *req)
···
 	int ret;
 
 	init_task_work(&req->task_work, io_req_task_submit);
+	percpu_ref_get(&req->ctx->refs);
 
 	ret = io_req_task_work_add(req, &req->task_work);
 	if (unlikely(ret)) {
···
 		req->flags &= ~REQ_F_TASK_PINNED;
 	}
 
-	io_dismantle_req(req);
+	WARN_ON_ONCE(io_dismantle_req(req));
 	rb->reqs[rb->to_free++] = req;
 	if (unlikely(rb->to_free == ARRAY_SIZE(rb->reqs)))
 		__io_req_free_batch_flush(req->ctx, rb);
···
 	ret = io_import_iovec(rw, req, &iovec, &iter, false);
 	if (ret < 0)
 		goto end_req;
-	ret = io_setup_async_rw(req, ret, iovec, inline_vecs, &iter);
+	ret = io_setup_async_rw(req, iovec, inline_vecs, &iter, false);
 	if (!ret)
 		return true;
 	kfree(iovec);
···
 		refcount_inc(&req->refs);
 		io_queue_async_work(req);
 	}
+
+	percpu_ref_put(&ctx->refs);
 }
 #endif
 
···
 		return false;
 
 	init_task_work(&req->task_work, io_rw_resubmit);
+	percpu_ref_get(&req->ctx->refs);
+
 	ret = io_req_task_work_add(req, &req->task_work);
 	if (!ret)
 		return true;
···
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);
 
+	/* add previously done IO, if any */
+	if (req->io && req->io->rw.bytes_done > 0) {
+		if (ret < 0)
+			ret = req->io->rw.bytes_done;
+		else
+			ret += req->io->rw.bytes_done;
+	}
+
 	if (req->flags & REQ_F_CUR_POS)
 		req->file->f_pos = kiocb->ki_pos;
 	if (ret >= 0 && kiocb->ki_complete == io_complete_rw)
···
 	ssize_t ret;
 	u8 opcode;
 
+	if (req->io) {
+		struct io_async_rw *iorw = &req->io->rw;
+
+		*iovec = NULL;
+		return iov_iter_count(&iorw->iter);
+	}
+
 	opcode = req->opcode;
 	if (opcode == IORING_OP_READ_FIXED || opcode == IORING_OP_WRITE_FIXED) {
 		*iovec = NULL;
···
 		ret = import_single_range(rw, buf, sqe_len, *iovec, iter);
 		*iovec = NULL;
 		return ret < 0 ? ret : sqe_len;
-	}
-
-	if (req->io) {
-		struct io_async_rw *iorw = &req->io->rw;
-
-		iov_iter_init(iter, rw, iorw->iov, iorw->nr_segs, iorw->size);
-		*iovec = NULL;
-		return iorw->size;
 	}
 
 	if (req->flags & REQ_F_BUFFER_SELECT) {
···
 	return ret;
 }
 
-static void io_req_map_rw(struct io_kiocb *req, ssize_t io_size,
-			  struct iovec *iovec, struct iovec *fast_iov,
-			  struct iov_iter *iter)
+static void io_req_map_rw(struct io_kiocb *req, const struct iovec *iovec,
+			  const struct iovec *fast_iov, struct iov_iter *iter)
 {
 	struct io_async_rw *rw = &req->io->rw;
 
-	rw->nr_segs = iter->nr_segs;
-	rw->size = io_size;
+	memcpy(&rw->iter, iter, sizeof(*iter));
+	rw->free_iovec = NULL;
+	rw->bytes_done = 0;
+	/* can only be fixed buffers, no need to do anything */
+	if (iter->type == ITER_BVEC)
+		return;
 	if (!iovec) {
-		rw->iov = rw->fast_iov;
-		if (rw->iov != fast_iov)
-			memcpy(rw->iov, fast_iov,
+		unsigned iov_off = 0;
+
+		rw->iter.iov = rw->fast_iov;
+		if (iter->iov != fast_iov) {
+			iov_off = iter->iov - fast_iov;
+			rw->iter.iov += iov_off;
+		}
+		if (rw->fast_iov != fast_iov)
+			memcpy(rw->fast_iov + iov_off, fast_iov + iov_off,
 			       sizeof(struct iovec) * iter->nr_segs);
 	} else {
-		rw->iov = iovec;
+		rw->free_iovec = iovec;
 		req->flags |= REQ_F_NEED_CLEANUP;
 	}
 }
···
 	return  __io_alloc_async_ctx(req);
 }
 
-static int io_setup_async_rw(struct io_kiocb *req, ssize_t io_size,
-			     struct iovec *iovec, struct iovec *fast_iov,
-			     struct iov_iter *iter)
+static int io_setup_async_rw(struct io_kiocb *req, const struct iovec *iovec,
+			     const struct iovec *fast_iov,
+			     struct iov_iter *iter, bool force)
 {
-	if (!io_op_defs[req->opcode].async_ctx)
+	if (!force && !io_op_defs[req->opcode].async_ctx)
 		return 0;
 	if (!req->io) {
 		if (__io_alloc_async_ctx(req))
 			return -ENOMEM;
 
-		io_req_map_rw(req, io_size, iovec, fast_iov, iter);
+		io_req_map_rw(req, iovec, fast_iov, iter);
 	}
 	return 0;
 }
···
 static inline int io_rw_prep_async(struct io_kiocb *req, int rw,
 				   bool force_nonblock)
 {
-	struct io_async_ctx *io = req->io;
-	struct iov_iter iter;
+	struct io_async_rw *iorw = &req->io->rw;
 	ssize_t ret;
 
-	io->rw.iov = io->rw.fast_iov;
+	iorw->iter.iov = iorw->fast_iov;
+	/* reset ->io around the iovec import, we don't want to use it */
 	req->io = NULL;
-	ret = io_import_iovec(rw, req, &io->rw.iov, &iter, !force_nonblock);
-	req->io = io;
+	ret = io_import_iovec(rw, req, (struct iovec **) &iorw->iter.iov,
+				&iorw->iter, !force_nonblock);
+	req->io = container_of(iorw, struct io_async_ctx, rw);
 	if (unlikely(ret < 0))
 		return ret;
 
-	io_req_map_rw(req, ret, io->rw.iov, io->rw.fast_iov, &iter);
+	io_req_map_rw(req, iorw->iter.iov, iorw->fast_iov, &iorw->iter);
 	return 0;
 }
 
···
 	return io_rw_prep_async(req, READ, force_nonblock);
 }
 
+/*
+ * This is our waitqueue callback handler, registered through lock_page_async()
+ * when we initially tried to do the IO with the iocb armed our waitqueue.
+ * This gets called when the page is unlocked, and we generally expect that to
+ * happen when the page IO is completed and the page is now uptodate. This will
+ * queue a task_work based retry of the operation, attempting to copy the data
+ * again. If the latter fails because the page was NOT uptodate, then we will
+ * do a thread based blocking retry of the operation. That's the unexpected
+ * slow path.
+ */
 static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode,
 			     int sync, void *arg)
 {
···
 	if (!wake_page_match(wpq, key))
 		return 0;
 
-	/* Stop waking things up if the page is locked again */
-	if (test_bit(key->bit_nr, &key->page->flags))
-		return -1;
-
 	list_del_init(&wait->entry);
 
 	init_task_work(&req->task_work, io_req_task_submit);
+	percpu_ref_get(&req->ctx->refs);
+
 	/* submit ref gets dropped, acquire a new one */
 	refcount_inc(&req->refs);
 	ret = io_req_task_work_add(req, &req->task_work);
···
 	return -EOPNOTSUPP;
 }
 
-
+/*
+ * This controls whether a given IO request should be armed for async page
+ * based retry. If we return false here, the request is handed to the async
+ * worker threads for retry. If we're doing buffered reads on a regular file,
+ * we prepare a private wait_page_queue entry and retry the operation. This
+ * will either succeed because the page is now uptodate and unlocked, or it
+ * will register a callback when the page is unlocked at IO completion. Through
+ * that callback, io_uring uses task_work to setup a retry of the operation.
+ * That retry will attempt the buffered read again. The retry will generally
+ * succeed, or in rare cases where it fails, we then fall back to using the
+ * async worker threads for a blocking retry.
+ */
 static bool io_rw_should_retry(struct io_kiocb *req)
 {
 	struct kiocb *kiocb = &req->rw.kiocb;
···
 	if (req->flags & REQ_F_NOWAIT)
 		return false;
 
-	/* already tried, or we're doing O_DIRECT */
-	if (kiocb->ki_flags & (IOCB_DIRECT | IOCB_WAITQ))
+	/* Only for buffered IO */
+	if (kiocb->ki_flags & IOCB_DIRECT)
 		return false;
 	/*
 	 * just use poll if we can, and don't attempt if the fs doesn't
 	 * support callback based unlocks
 	 */
 	if (file_can_poll(req->file) || !(req->file->f_mode & FMODE_BUF_RASYNC))
-		return false;
-
-	/*
-	 * If request type doesn't require req->io to defer in general,
-	 * we need to allocate it here
-	 */
-	if (!req->io && __io_alloc_async_ctx(req))
 		return false;
 
 	ret = kiocb_wait_page_queue_init(kiocb, &req->io->rw.wpq,
···
 {
 	if (req->file->f_op->read_iter)
 		return call_read_iter(req->file, &req->rw.kiocb, iter);
-	return loop_rw_iter(READ, req->file, &req->rw.kiocb, iter);
+	else if (req->file->f_op->read)
+		return loop_rw_iter(READ, req->file, &req->rw.kiocb, iter);
+	else
+		return -EINVAL;
 }
 
 static int io_read(struct io_kiocb *req, bool force_nonblock,
···
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw.kiocb;
-	struct iov_iter iter;
-	size_t iov_count;
+	struct iov_iter __iter, *iter = &__iter;
 	ssize_t io_size, ret, ret2;
-	unsigned long nr_segs;
+	size_t iov_count;
 
-	ret = io_import_iovec(READ, req, &iovec, &iter, !force_nonblock);
+	if (req->io)
+		iter = &req->io->rw.iter;
+
+	ret = io_import_iovec(READ, req, &iovec, iter, !force_nonblock);
 	if (ret < 0)
 		return ret;
 	io_size = ret;
 	req->result = io_size;
+	ret = 0;
 
 	/* Ensure we clear previously set non-block flag */
 	if (!force_nonblock)
···
 	if (force_nonblock && !io_file_supports_async(req->file, READ))
 		goto copy_iov;
 
-	iov_count = iov_iter_count(&iter);
-	nr_segs = iter.nr_segs;
+	iov_count = iov_iter_count(iter);
 	ret = rw_verify_area(READ, req->file, &kiocb->ki_pos, iov_count);
 	if (unlikely(ret))
 		goto out_free;
 
-	ret2 = io_iter_do_read(req, &iter);
+	ret = io_iter_do_read(req, iter);
 
-	/* Catch -EAGAIN return for forced non-blocking submission */
-	if (!force_nonblock || (ret2 != -EAGAIN && ret2 != -EIO)) {
-		kiocb_done(kiocb, ret2, cs);
-	} else {
-		iter.count = iov_count;
-		iter.nr_segs = nr_segs;
-copy_iov:
-		ret = io_setup_async_rw(req, io_size, iovec, inline_vecs,
-					&iter);
+	if (!ret) {
+		goto done;
+	} else if (ret == -EIOCBQUEUED) {
+		ret = 0;
+		goto out_free;
+	} else if (ret == -EAGAIN) {
+		if (!force_nonblock)
+			goto done;
+		ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
 		if (ret)
 			goto out_free;
-		/* it's copied and will be cleaned with ->io */
-		iovec = NULL;
-		/* if we can retry, do so with the callbacks armed */
-		if (io_rw_should_retry(req)) {
-			ret2 = io_iter_do_read(req, &iter);
-			if (ret2 == -EIOCBQUEUED) {
-				goto out_free;
-			} else if (ret2 != -EAGAIN) {
-				kiocb_done(kiocb, ret2, cs);
-				goto out_free;
-			}
-		}
+		return -EAGAIN;
+	} else if (ret < 0) {
+		goto out_free;
+	}
+
+	/* read it all, or we did blocking attempt. no retry. */
+	if (!iov_iter_count(iter) || !force_nonblock ||
+	    (req->file->f_flags & O_NONBLOCK))
+		goto done;
+
+	io_size -= ret;
+copy_iov:
+	ret2 = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
+	if (ret2) {
+		ret = ret2;
+		goto out_free;
+	}
+	/* it's copied and will be cleaned with ->io */
+	iovec = NULL;
+	/* now use our persistent iterator, if we aren't already */
+	iter = &req->io->rw.iter;
+retry:
+	req->io->rw.bytes_done += ret;
+	/* if we can retry, do so with the callbacks armed */
+	if (!io_rw_should_retry(req)) {
 		kiocb->ki_flags &= ~IOCB_WAITQ;
 		return -EAGAIN;
 	}
+
+	/*
+	 * Now retry read with the IOCB_WAITQ parts set in the iocb. If we
+	 * get -EIOCBQUEUED, then we'll get a notification when the desired
+	 * page gets unlocked. We can also get a partial read here, and if we
+	 * do, then just retry at the new offset.
+	 */
+	ret = io_iter_do_read(req, iter);
+	if (ret == -EIOCBQUEUED) {
+		ret = 0;
+		goto out_free;
+	} else if (ret > 0 && ret < io_size) {
+		/* we got some bytes, but not all. retry. */
+		goto retry;
+	}
+done:
+	kiocb_done(kiocb, ret, cs);
+	ret = 0;
 out_free:
 	if (iovec)
 		kfree(iovec);
···
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw.kiocb;
-	struct iov_iter iter;
+	struct iov_iter __iter, *iter = &__iter;
 	size_t iov_count;
 	ssize_t ret, ret2, io_size;
-	unsigned long nr_segs;
 
-	ret = io_import_iovec(WRITE, req, &iovec, &iter, !force_nonblock);
+	if (req->io)
+		iter = &req->io->rw.iter;
+
+	ret = io_import_iovec(WRITE, req, &iovec, iter, !force_nonblock);
 	if (ret < 0)
 		return ret;
 	io_size = ret;
···
 	    (req->flags & REQ_F_ISREG))
 		goto copy_iov;
 
-	iov_count = iov_iter_count(&iter);
-	nr_segs = iter.nr_segs;
+	iov_count = iov_iter_count(iter);
 	ret = rw_verify_area(WRITE, req->file, &kiocb->ki_pos, iov_count);
 	if (unlikely(ret))
 		goto out_free;
···
 	kiocb->ki_flags |= IOCB_WRITE;
 
 	if (req->file->f_op->write_iter)
-		ret2 = call_write_iter(req->file, kiocb, &iter);
+		ret2 = call_write_iter(req->file, kiocb, iter);
+	else if (req->file->f_op->write)
+		ret2 = loop_rw_iter(WRITE, req->file, kiocb, iter);
 	else
-		ret2 = loop_rw_iter(WRITE, req->file, kiocb, &iter);
+		ret2 = -EINVAL;
 
 	/*
 	 * Raw bdev writes will return -EOPNOTSUPP for IOCB_NOWAIT. Just
···
 	if (!force_nonblock || ret2 != -EAGAIN) {
 		kiocb_done(kiocb, ret2, cs);
 	} else {
-		iter.count = iov_count;
-		iter.nr_segs = nr_segs;
 copy_iov:
-		ret = io_setup_async_rw(req, io_size, iovec, inline_vecs,
-					&iter);
-		if (ret)
-			goto out_free;
-		/* it's copied and will be cleaned with ->io */
-		iovec = NULL;
-		return -EAGAIN;
+		ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
+		if (!ret)
+			return -EAGAIN;
 	}
 out_free:
 	if (iovec)
···
 
 	req->result = mask;
 	init_task_work(&req->task_work, func);
+	percpu_ref_get(&req->ctx->refs);
+
 	/*
 	 * If this fails, then the task is exiting. When a task exits, the
 	 * work gets canceled, so just cancel this request as well instead
···
 	return false;
 }
 
-static void io_poll_remove_double(struct io_kiocb *req, void *data)
+static struct io_poll_iocb *io_poll_get_double(struct io_kiocb *req)
 {
-	struct io_poll_iocb *poll = data;
+	/* pure poll stashes this in ->io, poll driven retry elsewhere */
+	if (req->opcode == IORING_OP_POLL_ADD)
+		return (struct io_poll_iocb *) req->io;
+	return req->apoll->double_poll;
+}
+
+static struct io_poll_iocb *io_poll_get_single(struct io_kiocb *req)
+{
+	if (req->opcode == IORING_OP_POLL_ADD)
+		return &req->poll;
+	return &req->apoll->poll;
+}
+
+static void io_poll_remove_double(struct io_kiocb *req)
+{
+	struct io_poll_iocb *poll = io_poll_get_double(req);
 
 	lockdep_assert_held(&req->ctx->completion_lock);
 
···
 {
 	struct io_ring_ctx *ctx = req->ctx;
 
-	io_poll_remove_double(req, req->io);
+	io_poll_remove_double(req);
 	req->poll.done = true;
 	io_cqring_fill_event(req, error ? error : mangle_poll(mask));
 	io_commit_cqring(ctx);
···
 static void io_poll_task_func(struct callback_head *cb)
 {
 	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
+	struct io_ring_ctx *ctx = req->ctx;
 	struct io_kiocb *nxt = NULL;
 
 	io_poll_task_handler(req, &nxt);
 	if (nxt)
 		__io_req_task_submit(nxt);
+	percpu_ref_put(&ctx->refs);
 }
 
 static int io_poll_double_wake(struct wait_queue_entry *wait, unsigned mode,
 			       int sync, void *key)
 {
 	struct io_kiocb *req = wait->private;
-	struct io_poll_iocb *poll = req->apoll->double_poll;
+	struct io_poll_iocb *poll = io_poll_get_single(req);
 	__poll_t mask = key_to_poll(key);
 
 	/* for instances that support it check for an event match first: */
···
 		done = list_empty(&poll->wait.entry);
 		if (!done)
 			list_del_init(&poll->wait.entry);
+		/* make sure double remove sees this as being gone */
+		wait->private = NULL;
 		spin_unlock(&poll->head->lock);
 		if (!done)
 			__io_async_wake(req, poll, mask, io_poll_task_func);
···
 
 	if (io_poll_rewait(req, &apoll->poll)) {
 		spin_unlock_irq(&ctx->completion_lock);
+		percpu_ref_put(&ctx->refs);
 		return;
 	}
 
···
 	if (hash_hashed(&req->hash_node))
 		hash_del(&req->hash_node);
 
-	io_poll_remove_double(req, apoll->double_poll);
+	io_poll_remove_double(req);
 	spin_unlock_irq(&ctx->completion_lock);
 
 	if (!READ_ONCE(apoll->poll.canceled))
···
 	else
 		__io_req_task_cancel(req, -ECANCELED);
 
+	percpu_ref_put(&ctx->refs);
 	kfree(apoll->double_poll);
 	kfree(apoll);
 }
···
 
 	ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
 					io_async_wake);
-	if (ret) {
-		io_poll_remove_double(req, apoll->double_poll);
+	if (ret || ipt.error) {
+		io_poll_remove_double(req);
 		spin_unlock_irq(&ctx->completion_lock);
 		kfree(apoll->double_poll);
 		kfree(apoll);
···
 {
 	bool do_complete;
 
+	io_poll_remove_double(req);
+
 	if (req->opcode == IORING_OP_POLL_ADD) {
-		io_poll_remove_double(req, req->io);
 		do_complete = __io_poll_remove_one(req, &req->poll);
 	} else {
 		struct async_poll *apoll = req->apoll;
-
-		io_poll_remove_double(req, apoll->double_poll);
 
 		/* non-poll requests have submit ref still */
 		do_complete = __io_poll_remove_one(req, &apoll->poll);
···
 		io_cqring_fill_event(req, -ECANCELED);
 		io_commit_cqring(req->ctx);
 		req->flags |= REQ_F_COMP_LOCKED;
+		req_set_fail_links(req);
 		io_put_req(req);
 	}
 
···
 	return HRTIMER_NORESTART;
 }
 
+static int __io_timeout_cancel(struct io_kiocb *req)
+{
+	int ret;
+
+	list_del_init(&req->timeout.list);
+
+	ret = hrtimer_try_to_cancel(&req->io->timeout.timer);
+	if (ret == -1)
+		return -EALREADY;
+
+	req_set_fail_links(req);
+	req->flags |= REQ_F_COMP_LOCKED;
+	io_cqring_fill_event(req, -ECANCELED);
+	io_put_req(req);
+	return 0;
+}
+
 static int io_timeout_cancel(struct io_ring_ctx *ctx, __u64 user_data)
 {
 	struct io_kiocb *req;
···
 
 	list_for_each_entry(req, &ctx->timeout_list, timeout.list) {
 		if (user_data == req->user_data) {
-			list_del_init(&req->timeout.list);
 			ret = 0;
 			break;
 		}
···
 	if (ret == -ENOENT)
 		return ret;
 
-	ret = hrtimer_try_to_cancel(&req->io->timeout.timer);
-	if (ret == -1)
-		return -EALREADY;
-
-	req_set_fail_links(req);
-	io_cqring_fill_event(req, -ECANCELED);
-	io_put_req(req);
-	return 0;
+	return __io_timeout_cancel(req);
 }
 
 static int io_timeout_remove_prep(struct io_kiocb *req,
···
 		case IORING_OP_WRITEV:
 		case IORING_OP_WRITE_FIXED:
 		case IORING_OP_WRITE:
-			if (io->rw.iov != io->rw.fast_iov)
-				kfree(io->rw.iov);
+			if (io->rw.free_iovec)
+				kfree(io->rw.free_iovec);
 			break;
 		case IORING_OP_RECVMSG:
 		case IORING_OP_SENDMSG:
···
 	return HRTIMER_NORESTART;
 }
 
-static void io_queue_linked_timeout(struct io_kiocb *req)
+static void __io_queue_linked_timeout(struct io_kiocb *req)
 {
-	struct io_ring_ctx *ctx = req->ctx;
-
 	/*
 	 * If the list is now empty, then our linked request finished before
 	 * we got a chance to setup the timer
 	 */
-	spin_lock_irq(&ctx->completion_lock);
 	if (!list_empty(&req->link_list)) {
 		struct io_timeout_data *data = &req->io->timeout;
 
···
 		hrtimer_start(&data->timer, timespec64_to_ktime(data->ts),
 				data->mode);
 	}
+}
+
+static void io_queue_linked_timeout(struct io_kiocb *req)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	spin_lock_irq(&ctx->completion_lock);
+	__io_queue_linked_timeout(req);
 	spin_unlock_irq(&ctx->completion_lock);
 
 	/* drop submission reference */
···
 	return work->files == files;
 }
 
+/*
+ * Returns true if 'preq' is the link parent of 'req'
+ */
+static bool io_match_link(struct io_kiocb *preq, struct io_kiocb *req)
+{
+	struct io_kiocb *link;
+
+	if (!(preq->flags & REQ_F_LINK_HEAD))
+		return false;
+
+	list_for_each_entry(link, &preq->link_list, link_list) {
+		if (link == req)
+			return true;
+	}
+
+	return false;
+}
+
+/*
+ * We're looking to cancel 'req' because it's holding on to our files, but
+ * 'req' could be a link to another request. See if it is, and cancel that
+ * parent request if so.
+ */
+static bool io_poll_remove_link(struct io_ring_ctx *ctx, struct io_kiocb *req)
+{
+	struct hlist_node *tmp;
+	struct io_kiocb *preq;
+	bool found = false;
+	int i;
+
+	spin_lock_irq(&ctx->completion_lock);
+	for (i = 0; i < (1U << ctx->cancel_hash_bits); i++) {
+		struct hlist_head *list;
+
+		list = &ctx->cancel_hash[i];
+		hlist_for_each_entry_safe(preq, tmp, list, hash_node) {
+			found = io_match_link(preq, req);
+			if (found) {
+				io_poll_remove_one(preq);
+				break;
+			}
+		}
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+	return found;
+}
+
+static bool io_timeout_remove_link(struct io_ring_ctx *ctx,
+				   struct io_kiocb *req)
+{
+	struct io_kiocb *preq;
+	bool found = false;
+
+	spin_lock_irq(&ctx->completion_lock);
+	list_for_each_entry(preq, &ctx->timeout_list, timeout.list) {
+		found = io_match_link(preq, req);
+		if (found) {
+			__io_timeout_cancel(preq);
+			break;
+		}
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+	return found;
+}
+
 static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 				  struct files_struct *files)
 {
···
 			}
 		} else {
 			io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
+			/* could be a link, check and remove if it is */
+			if (!io_poll_remove_link(ctx, cancel_req))
+				io_timeout_remove_link(ctx, cancel_req);
 			io_put_req(cancel_req);
 		}
 
···
 	struct io_rings *rings;
 	size_t size, sq_array_offset;
 
+	/* make sure these are sane, as we already accounted them */
+	ctx->sq_entries = p->sq_entries;
+	ctx->cq_entries = p->cq_entries;
+
 	size = rings_size(p->sq_entries, p->cq_entries, &sq_array_offset);
 	if (size == SIZE_MAX)
 		return -EOVERFLOW;
···
 	rings->cq_ring_entries = p->cq_entries;
 	ctx->sq_mask = rings->sq_ring_mask;
 	ctx->cq_mask = rings->cq_ring_mask;
-	ctx->sq_entries = rings->sq_ring_entries;
-	ctx->cq_entries = rings->cq_ring_entries;
 
 	size = array_size(sizeof(struct io_uring_sqe), p->sq_entries);
 	if (size == SIZE_MAX) {
···
 	ctx->user = user;
 	ctx->creds = get_current_cred();
 
+	/*
+	 * Account memory _before_ installing the file descriptor. Once
+	 * the descriptor is installed, it can get closed at any time. Also
+	 * do this before hitting the general error path, as ring freeing
+	 * will un-account as well.
+	 */
+	io_account_mem(ctx, ring_pages(p->sq_entries, p->cq_entries),
+		       ACCT_LOCKED);
+	ctx->limit_mem = limit_mem;
+
 	ret = io_allocate_scq_urings(ctx, p);
 	if (ret)
 		goto err;
···
 		ret = -EFAULT;
 		goto err;
 	}
-
-	/*
-	 * Account memory _before_ installing the file descriptor. Once
-	 * the descriptor is installed, it can get closed at any time.
-	 */
-	io_account_mem(ctx, ring_pages(p->sq_entries, p->cq_entries),
-		       ACCT_LOCKED);
-	ctx->limit_mem = limit_mem;
 
 	/*
 	 * Install ring fd as the very last thing, so we don't risk someone

include/linux/fs.h

···
 	if (flags & RWF_NOWAIT) {
 		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
 			return -EOPNOTSUPP;
-		kiocb_flags |= IOCB_NOWAIT;
+		kiocb_flags |= IOCB_NOWAIT | IOCB_NOIO;
 	}
 	if (flags & RWF_HIPRI)
 		kiocb_flags |= IOCB_HIPRI;

kernel/signal.c

···
 
 relock:
 	spin_lock_irq(&sighand->siglock);
-	current->jobctl &= ~JOBCTL_TASK_WORK;
+	/*
+	 * Make sure we can safely read ->jobctl() in task_work add. As Oleg
+	 * states:
+	 *
+	 * It pairs with mb (implied by cmpxchg) before READ_ONCE. So we
+	 * roughly have
+	 *
+	 *	task_work_add:				get_signal:
+	 *	STORE(task->task_works, new_work);	STORE(task->jobctl);
+	 *	mb();					mb();
+	 *	LOAD(task->jobctl);			LOAD(task->task_works);
+	 *
+	 * and we can rely on STORE-MB-LOAD [ in task_work_add].
+	 */
+	smp_store_mb(current->jobctl, current->jobctl & ~JOBCTL_TASK_WORK);
 	if (unlikely(current->task_works)) {
 		spin_unlock_irq(&sighand->siglock);
 		task_work_run();

kernel/task_work.c

···
 		set_notify_resume(task);
 		break;
 	case TWA_SIGNAL:
-		if (lock_task_sighand(task, &flags)) {
+		/*
+		 * Only grab the sighand lock if we don't already have some
+		 * task_work pending. This pairs with the smp_store_mb()
+		 * in get_signal(), see comment there.
+		 */
+		if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
+		    lock_task_sighand(task, &flags)) {
 			task->jobctl |= JOBCTL_TASK_WORK;
 			signal_wake_up(task, 0);
 			unlock_task_sighand(task, &flags);