1 files changed, 217 insertions, 116 deletions

diff --git a/fs/io_uring.c b/fs/io_uring.c
index bbdbd56cf2ac..84efb8956734 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4,15 +4,28 @@
  * supporting fast/efficient IO.
  *
  * A note on the read/write ordering memory barriers that are matched between
- * the application and kernel side. When the application reads the CQ ring
- * tail, it must use an appropriate smp_rmb() to order with the smp_wmb()
- * the kernel uses after writing the tail. Failure to do so could cause a
- * delay in when the application notices that completion events available.
- * This isn't a fatal condition. Likewise, the application must use an
- * appropriate smp_wmb() both before writing the SQ tail, and after writing
- * the SQ tail. The first one orders the sqe writes with the tail write, and
- * the latter is paired with the smp_rmb() the kernel will issue before
- * reading the SQ tail on submission.
+ * the application and kernel side.
+ *
+ * After the application reads the CQ ring tail, it must use an
+ * appropriate smp_rmb() to pair with the smp_wmb() the kernel uses
+ * before writing the tail (using smp_load_acquire to read the tail will
+ * do). It also needs a smp_mb() before updating CQ head (ordering the
+ * entry load(s) with the head store), pairing with an implicit barrier
+ * through a control-dependency in io_get_cqring (smp_store_release to
+ * store head will do). Failure to do so could lead to reading invalid
+ * CQ entries.
+ *
+ * Likewise, the application must use an appropriate smp_wmb() before
+ * writing the SQ tail (ordering SQ entry stores with the tail store),
+ * which pairs with smp_load_acquire in io_get_sqring (smp_store_release
+ * to store the tail will do). And it needs a barrier ordering the SQ
+ * head load before writing new SQ entries (smp_load_acquire to read
+ * head will do).
+ *
+ * When using the SQ poll thread (IORING_SETUP_SQPOLL), the application
+ * needs to check the SQ flags for IORING_SQ_NEED_WAKEUP *after*
+ * updating the SQ tail; a full memory barrier smp_mb() is needed
+ * between.
  *
  * Also see the examples in the liburing library:
  *
@@ -70,20 +83,108 @@ struct io_uring {
 	u32 tail ____cacheline_aligned_in_smp;
 };
 
+/*
+ * This data is shared with the application through the mmap at offset
+ * IORING_OFF_SQ_RING.
+ *
+ * The offsets to the member fields are published through struct
+ * io_sqring_offsets when calling io_uring_setup.
+ */
 struct io_sq_ring {
+	/*
+	 * Head and tail offsets into the ring; the offsets need to be
+	 * masked to get valid indices.
+	 *
+	 * The kernel controls head and the application controls tail.
+	 */
 	struct io_uring		r;
+	/*
+	 * Bitmask to apply to head and tail offsets (constant, equals
+	 * ring_entries - 1)
+	 */
 	u32			ring_mask;
+	/* Ring size (constant, power of 2) */
 	u32			ring_entries;
+	/*
+	 * Number of invalid entries dropped by the kernel due to
+	 * invalid index stored in array
+	 *
+	 * Written by the kernel, shouldn't be modified by the
+	 * application (i.e. get number of "new events" by comparing to
+	 * cached value).
+	 *
+	 * After a new SQ head value was read by the application this
+	 * counter includes all submissions that were dropped reaching
+	 * the new SQ head (and possibly more).
+	 */
 	u32			dropped;
+	/*
+	 * Runtime flags
+	 *
+	 * Written by the kernel, shouldn't be modified by the
+	 * application.
+	 *
+	 * The application needs a full memory barrier before checking
+	 * for IORING_SQ_NEED_WAKEUP after updating the sq tail.
+	 */
 	u32			flags;
+	/*
+	 * Ring buffer of indices into array of io_uring_sqe, which is
+	 * mmapped by the application using the IORING_OFF_SQES offset.
+	 *
+	 * This indirection could e.g. be used to assign fixed
+	 * io_uring_sqe entries to operations and only submit them to
+	 * the queue when needed.
+	 *
+	 * The kernel modifies neither the indices array nor the entries
+	 * array.
+	 */
 	u32			array[];
 };
 
+/*
+ * This data is shared with the application through the mmap at offset
+ * IORING_OFF_CQ_RING.
+ *
+ * The offsets to the member fields are published through struct
+ * io_cqring_offsets when calling io_uring_setup.
+ */
 struct io_cq_ring {
+	/*
+	 * Head and tail offsets into the ring; the offsets need to be
+	 * masked to get valid indices.
+	 *
+	 * The application controls head and the kernel tail.
+	 */
 	struct io_uring		r;
+	/*
+	 * Bitmask to apply to head and tail offsets (constant, equals
+	 * ring_entries - 1)
+	 */
 	u32			ring_mask;
+	/* Ring size (constant, power of 2) */
 	u32			ring_entries;
+	/*
+	 * Number of completion events lost because the queue was full;
+	 * this should be avoided by the application by making sure
+	 * there are not more requests pending thatn there is space in
+	 * the completion queue.
+	 *
+	 * Written by the kernel, shouldn't be modified by the
+	 * application (i.e. get number of "new events" by comparing to
+	 * cached value).
+	 *
+	 * As completion events come in out of order this counter is not
+	 * ordered with any other data.
+	 */
 	u32			overflow;
+	/*
+	 * Ring buffer of completion events.
+	 *
+	 * The kernel writes completion events fresh every time they are
+	 * produced, so the application is allowed to modify pending
+	 * entries.
+	 */
 	struct io_uring_cqe	cqes[];
 };
 
@@ -221,7 +322,7 @@ struct io_kiocb {
 	struct list_head	list;
 	unsigned int		flags;
 	refcount_t		refs;
-#define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
+#define REQ_F_NOWAIT		1	/* must not punt to workers */
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_FIXED_FILE	4	/* ctx owns file */
 #define REQ_F_SEQ_PREV		8	/* sequential with previous */
@@ -317,12 +418,6 @@ static void io_commit_cqring(struct io_ring_ctx *ctx)
 		/* order cqe stores with ring update */
 		smp_store_release(&ring->r.tail, ctx->cached_cq_tail);
 
-		/*
-		 * Write sider barrier of tail update, app has read side. See
-		 * comment at the top of this file.
-		 */
-		smp_wmb();
-
 		if (wq_has_sleeper(&ctx->cq_wait)) {
 			wake_up_interruptible(&ctx->cq_wait);
 			kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
@@ -336,9 +431,12 @@ static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx)
 	unsigned tail;
 
 	tail = ctx->cached_cq_tail;
-	/* See comment at the top of the file */
-	smp_rmb();
-	if (tail + 1 == READ_ONCE(ring->r.head))
+	/*
+	 * writes to the cq entry need to come after reading head; the
+	 * control dependency is enough as we're using WRITE_ONCE to
+	 * fill the cq entry
+	 */
+	if (tail - READ_ONCE(ring->r.head) == ring->ring_entries)
 		return NULL;
 
 	ctx->cached_cq_tail++;
@@ -682,11 +780,9 @@ static void io_iopoll_req_issued(struct io_kiocb *req)
 		list_add_tail(&req->list, &ctx->poll_list);
 }
 
-static void io_file_put(struct io_submit_state *state, struct file *file)
+static void io_file_put(struct io_submit_state *state)
 {
-	if (!state) {
-		fput(file);
-	} else if (state->file) {
+	if (state->file) {
 		int diff = state->has_refs - state->used_refs;
 
 		if (diff)
@@ -711,7 +807,7 @@ static struct file *io_file_get(struct io_submit_state *state, int fd)
 			state->ios_left--;
 			return state->file;
 		}
-		io_file_put(state, NULL);
+		io_file_put(state);
 	}
 	state->file = fget_many(fd, state->ios_left);
 	if (!state->file)
@@ -742,7 +838,7 @@ static bool io_file_supports_async(struct file *file)
 }
 
 static int io_prep_rw(struct io_kiocb *req, const struct sqe_submit *s,
-		      bool force_nonblock, struct io_submit_state *state)
+		      bool force_nonblock)
 {
 	const struct io_uring_sqe *sqe = s->sqe;
 	struct io_ring_ctx *ctx = req->ctx;
@@ -776,10 +872,14 @@ static int io_prep_rw(struct io_kiocb *req, const struct sqe_submit *s,
 	ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
 	if (unlikely(ret))
 		return ret;
-	if (force_nonblock) {
+
+	/* don't allow async punt if RWF_NOWAIT was requested */
+	if (kiocb->ki_flags & IOCB_NOWAIT)
+		req->flags |= REQ_F_NOWAIT;
+
+	if (force_nonblock)
 		kiocb->ki_flags |= IOCB_NOWAIT;
-		req->flags |= REQ_F_FORCE_NONBLOCK;
-	}
+
 	if (ctx->flags & IORING_SETUP_IOPOLL) {
 		if (!(kiocb->ki_flags & IOCB_DIRECT) ||
 		    !kiocb->ki_filp->f_op->iopoll)
@@ -940,7 +1040,7 @@ static void io_async_list_note(int rw, struct io_kiocb *req, size_t len)
 }
 
 static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
-		   bool force_nonblock, struct io_submit_state *state)
+		   bool force_nonblock)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw;
@@ -949,7 +1049,7 @@ static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
 	size_t iov_count;
 	int ret;
 
-	ret = io_prep_rw(req, s, force_nonblock, state);
+	ret = io_prep_rw(req, s, force_nonblock);
 	if (ret)
 		return ret;
 	file = kiocb->ki_filp;
@@ -987,7 +1087,7 @@ static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
 }
 
 static int io_write(struct io_kiocb *req, const struct sqe_submit *s,
-		    bool force_nonblock, struct io_submit_state *state)
+		    bool force_nonblock)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw;
@@ -996,7 +1096,7 @@ static int io_write(struct io_kiocb *req, const struct sqe_submit *s,
 	size_t iov_count;
 	int ret;
 
-	ret = io_prep_rw(req, s, force_nonblock, state);
+	ret = io_prep_rw(req, s, force_nonblock);
 	if (ret)
 		return ret;
 
@@ -1338,8 +1438,7 @@ static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 }
 
 static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
-			   const struct sqe_submit *s, bool force_nonblock,
-			   struct io_submit_state *state)
+			   const struct sqe_submit *s, bool force_nonblock)
 {
 	int ret, opcode;
 
@@ -1355,18 +1454,18 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	case IORING_OP_READV:
 		if (unlikely(s->sqe->buf_index))
 			return -EINVAL;
-		ret = io_read(req, s, force_nonblock, state);
+		ret = io_read(req, s, force_nonblock);
 		break;
 	case IORING_OP_WRITEV:
 		if (unlikely(s->sqe->buf_index))
 			return -EINVAL;
-		ret = io_write(req, s, force_nonblock, state);
+		ret = io_write(req, s, force_nonblock);
 		break;
 	case IORING_OP_READ_FIXED:
-		ret = io_read(req, s, force_nonblock, state);
+		ret = io_read(req, s, force_nonblock);
 		break;
 	case IORING_OP_WRITE_FIXED:
-		ret = io_write(req, s, force_nonblock, state);
+		ret = io_write(req, s, force_nonblock);
 		break;
 	case IORING_OP_FSYNC:
 		ret = io_fsync(req, s->sqe, force_nonblock);
@@ -1439,8 +1538,7 @@ restart:
 		struct sqe_submit *s = &req->submit;
 		const struct io_uring_sqe *sqe = s->sqe;
 
-		/* Ensure we clear previously set forced non-block flag */
-		req->flags &= ~REQ_F_FORCE_NONBLOCK;
+		/* Ensure we clear previously set non-block flag */
 		req->rw.ki_flags &= ~IOCB_NOWAIT;
 
 		ret = 0;
@@ -1459,7 +1557,7 @@ restart:
 			s->has_user = cur_mm != NULL;
 			s->needs_lock = true;
 			do {
-				ret = __io_submit_sqe(ctx, req, s, false, NULL);
+				ret = __io_submit_sqe(ctx, req, s, false);
 				/*
 				 * We can get EAGAIN for polled IO even though
 				 * we're forcing a sync submission from here,
@@ -1470,10 +1568,11 @@ restart:
 					break;
 				cond_resched();
 			} while (1);
-
-			/* drop submission reference */
-			io_put_req(req);
 		}
+
+		/* drop submission reference */
+		io_put_req(req);
+
 		if (ret) {
 			io_cqring_add_event(ctx, sqe->user_data, ret, 0);
 			io_put_req(req);
@@ -1625,8 +1724,8 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 	if (unlikely(ret))
 		goto out;
 
-	ret = __io_submit_sqe(ctx, req, s, true, state);
-	if (ret == -EAGAIN) {
+	ret = __io_submit_sqe(ctx, req, s, true);
+	if (ret == -EAGAIN && !(req->flags & REQ_F_NOWAIT)) {
 		struct io_uring_sqe *sqe_copy;
 
 		sqe_copy = kmalloc(sizeof(*sqe_copy), GFP_KERNEL);
@@ -1671,7 +1770,7 @@ out:
 static void io_submit_state_end(struct io_submit_state *state)
 {
 	blk_finish_plug(&state->plug);
-	io_file_put(state, NULL);
+	io_file_put(state);
 	if (state->free_reqs)
 		kmem_cache_free_bulk(req_cachep, state->free_reqs,
 					&state->reqs[state->cur_req]);
@@ -1700,24 +1799,10 @@ static void io_commit_sqring(struct io_ring_ctx *ctx)
 		 * write new data to them.
 		 */
 		smp_store_release(&ring->r.head, ctx->cached_sq_head);
-
-		/*
-		 * write side barrier of head update, app has read side. See
-		 * comment at the top of this file
-		 */
-		smp_wmb();
 	}
 }
 
 /*
- * Undo last io_get_sqring()
- */
-static void io_drop_sqring(struct io_ring_ctx *ctx)
-{
-	ctx->cached_sq_head--;
-}
-
-/*
  * Fetch an sqe, if one is available. Note that s->sqe will point to memory
  * that is mapped by userspace. This means that care needs to be taken to
  * ensure that reads are stable, as we cannot rely on userspace always
@@ -1739,9 +1824,8 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	 *    though the application is the one updating it.
 	 */
 	head = ctx->cached_sq_head;
-	/* See comment at the top of this file */
-	smp_rmb();
-	if (head == READ_ONCE(ring->r.tail))
+	/* make sure SQ entry isn't read before tail */
+	if (head == smp_load_acquire(&ring->r.tail))
 		return false;
 
 	head = READ_ONCE(ring->array[head & ctx->sq_mask]);
@@ -1755,8 +1839,6 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	/* drop invalid entries */
 	ctx->cached_sq_head++;
 	ring->dropped++;
-	/* See comment at the top of this file */
-	smp_wmb();
 	return false;
 }
 
@@ -1866,7 +1948,8 @@ static int io_sq_thread(void *data)
 
 			/* Tell userspace we may need a wakeup call */
 			ctx->sq_ring->flags |= IORING_SQ_NEED_WAKEUP;
-			smp_wmb();
+			/* make sure to read SQ tail after writing flags */
+			smp_mb();
 
 			if (!io_get_sqring(ctx, &sqes[0])) {
 				if (kthread_should_stop()) {
@@ -1879,13 +1962,11 @@ static int io_sq_thread(void *data)
 				finish_wait(&ctx->sqo_wait, &wait);
 
 				ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
-				smp_wmb();
 				continue;
 			}
 			finish_wait(&ctx->sqo_wait, &wait);
 
 			ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
-			smp_wmb();
 		}
 
 		i = 0;
@@ -1920,13 +2001,17 @@ static int io_sq_thread(void *data)
 		unuse_mm(cur_mm);
 		mmput(cur_mm);
 	}
+
+	if (kthread_should_park())
+		kthread_parkme();
+
 	return 0;
 }
 
 static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 {
 	struct io_submit_state state, *statep = NULL;
-	int i, ret = 0, submit = 0;
+	int i, submit = 0;
 
 	if (to_submit > IO_PLUG_THRESHOLD) {
 		io_submit_state_start(&state, ctx, to_submit);
@@ -1935,6 +2020,7 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 
 	for (i = 0; i < to_submit; i++) {
 		struct sqe_submit s;
+		int ret;
 
 		if (!io_get_sqring(ctx, &s))
 			break;
@@ -1942,21 +2028,18 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 		s.has_user = true;
 		s.needs_lock = false;
 		s.needs_fixed_file = false;
+		submit++;
 
 		ret = io_submit_sqe(ctx, &s, statep);
-		if (ret) {
-			io_drop_sqring(ctx);
-			break;
-		}
-
-		submit++;
+		if (ret)
+			io_cqring_add_event(ctx, s.sqe->user_data, ret, 0);
 	}
 	io_commit_sqring(ctx);
 
 	if (statep)
 		io_submit_state_end(statep);
 
-	return submit ? submit : ret;
+	return submit;
 }
 
 static unsigned io_cqring_events(struct io_cq_ring *ring)
@@ -2054,6 +2137,7 @@ static void io_sq_thread_stop(struct io_ring_ctx *ctx)
 	if (ctx->sqo_thread) {
 		ctx->sqo_stop = 1;
 		mb();
+		kthread_park(ctx->sqo_thread);
 		kthread_stop(ctx->sqo_thread);
 		ctx->sqo_thread = NULL;
 	}
@@ -2215,6 +2299,7 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 			fput(ctx->user_files[i]);
 
 		kfree(ctx->user_files);
+		ctx->user_files = NULL;
 		ctx->nr_user_files = 0;
 		return ret;
 	}
@@ -2235,19 +2320,23 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
 	mmgrab(current->mm);
 	ctx->sqo_mm = current->mm;
 
-	ctx->sq_thread_idle = msecs_to_jiffies(p->sq_thread_idle);
-	if (!ctx->sq_thread_idle)
-		ctx->sq_thread_idle = HZ;
+	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		ret = -EPERM;
+		if (!capable(CAP_SYS_ADMIN))
+			goto err;
 
-	ret = -EINVAL;
-	if (!cpu_possible(p->sq_thread_cpu))
-		goto err;
+		ctx->sq_thread_idle = msecs_to_jiffies(p->sq_thread_idle);
+		if (!ctx->sq_thread_idle)
+			ctx->sq_thread_idle = HZ;
 
-	if (ctx->flags & IORING_SETUP_SQPOLL) {
 		if (p->flags & IORING_SETUP_SQ_AFF) {
-			int cpu;
+			int cpu = array_index_nospec(p->sq_thread_cpu,
+							nr_cpu_ids);
+
+			ret = -EINVAL;
+			if (!cpu_possible(cpu))
+				goto err;
 
-			cpu = array_index_nospec(p->sq_thread_cpu, NR_CPUS);
 			ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
 							ctx, cpu,
 							"io_uring-sq");
@@ -2308,8 +2397,12 @@ static int io_account_mem(struct user_struct *user, unsigned long nr_pages)
 
 static void io_mem_free(void *ptr)
 {
-	struct page *page = virt_to_head_page(ptr);
+	struct page *page;
+
+	if (!ptr)
+		return;
 
+	page = virt_to_head_page(ptr);
 	if (put_page_testzero(page))
 		free_compound_page(page);
 }
@@ -2350,7 +2443,7 @@ static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
 
 		if (ctx->account_mem)
 			io_unaccount_mem(ctx->user, imu->nr_bvecs);
-		kfree(imu->bvec);
+		kvfree(imu->bvec);
 		imu->nr_bvecs = 0;
 	}
 
@@ -2442,9 +2535,9 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 		if (!pages || nr_pages > got_pages) {
 			kfree(vmas);
 			kfree(pages);
-			pages = kmalloc_array(nr_pages, sizeof(struct page *),
+			pages = kvmalloc_array(nr_pages, sizeof(struct page *),
 						GFP_KERNEL);
-			vmas = kmalloc_array(nr_pages,
+			vmas = kvmalloc_array(nr_pages,
 					sizeof(struct vm_area_struct *),
 					GFP_KERNEL);
 			if (!pages || !vmas) {
@@ -2456,7 +2549,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 			got_pages = nr_pages;
 		}
 
-		imu->bvec = kmalloc_array(nr_pages, sizeof(struct bio_vec),
+		imu->bvec = kvmalloc_array(nr_pages, sizeof(struct bio_vec),
 						GFP_KERNEL);
 		ret = -ENOMEM;
 		if (!imu->bvec) {
@@ -2495,6 +2588,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 			}
 			if (ctx->account_mem)
 				io_unaccount_mem(ctx->user, nr_pages);
+			kvfree(imu->bvec);
 			goto err;
 		}
 
@@ -2517,12 +2611,12 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 
 		ctx->nr_user_bufs++;
 	}
-	kfree(pages);
-	kfree(vmas);
+	kvfree(pages);
+	kvfree(vmas);
 	return 0;
 err:
-	kfree(pages);
-	kfree(vmas);
+	kvfree(pages);
+	kvfree(vmas);
 	io_sqe_buffer_unregister(ctx);
 	return ret;
 }
@@ -2560,9 +2654,13 @@ static __poll_t io_uring_poll(struct file *file, poll_table *wait)
 	__poll_t mask = 0;
 
 	poll_wait(file, &ctx->cq_wait, wait);
-	/* See comment at the top of this file */
+	/*
+	 * synchronizes with barrier from wq_has_sleeper call in
+	 * io_commit_cqring
+	 */
 	smp_rmb();
-	if (READ_ONCE(ctx->sq_ring->r.tail) + 1 != ctx->cached_sq_head)
+	if (READ_ONCE(ctx->sq_ring->r.tail) - ctx->cached_sq_head !=
+	    ctx->sq_ring->ring_entries)
 		mask |= EPOLLOUT | EPOLLWRNORM;
 	if (READ_ONCE(ctx->cq_ring->r.head) != ctx->cached_cq_tail)
 		mask |= EPOLLIN | EPOLLRDNORM;
@@ -2673,24 +2771,12 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 		mutex_lock(&ctx->uring_lock);
 		submitted = io_ring_submit(ctx, to_submit);
 		mutex_unlock(&ctx->uring_lock);
-
-		if (submitted < 0)
-			goto out_ctx;
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
 		unsigned nr_events = 0;
 
 		min_complete = min(min_complete, ctx->cq_entries);
 
-		/*
-		 * The application could have included the 'to_submit' count
-		 * in how many events it wanted to wait for. If we failed to
-		 * submit the desired count, we may need to adjust the number
-		 * of events to poll/wait for.
-		 */
-		if (submitted < to_submit)
-			min_complete = min_t(unsigned, submitted, min_complete);
-
 		if (ctx->flags & IORING_SETUP_IOPOLL) {
 			mutex_lock(&ctx->uring_lock);
 			ret = io_iopoll_check(ctx, &nr_events, min_complete);
@@ -2736,17 +2822,12 @@ static int io_allocate_scq_urings(struct io_ring_ctx *ctx,
 		return -EOVERFLOW;
 
 	ctx->sq_sqes = io_mem_alloc(size);
-	if (!ctx->sq_sqes) {
-		io_mem_free(ctx->sq_ring);
+	if (!ctx->sq_sqes)
 		return -ENOMEM;
-	}
 
 	cq_ring = io_mem_alloc(struct_size(cq_ring, cqes, p->cq_entries));
-	if (!cq_ring) {
-		io_mem_free(ctx->sq_ring);
-		io_mem_free(ctx->sq_sqes);
+	if (!cq_ring)
 		return -ENOMEM;
-	}
 
 	ctx->cq_ring = cq_ring;
 	cq_ring->ring_mask = p->cq_entries - 1;
@@ -2917,11 +2998,31 @@ SYSCALL_DEFINE2(io_uring_setup, u32, entries,
 
 static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			       void __user *arg, unsigned nr_args)
+	__releases(ctx->uring_lock)
+	__acquires(ctx->uring_lock)
 {
 	int ret;
 
+	/*
+	 * We're inside the ring mutex, if the ref is already dying, then
+	 * someone else killed the ctx or is already going through
+	 * io_uring_register().
+	 */
+	if (percpu_ref_is_dying(&ctx->refs))
+		return -ENXIO;
+
 	percpu_ref_kill(&ctx->refs);
+
+	/*
+	 * Drop uring mutex before waiting for references to exit. If another
+	 * thread is currently inside io_uring_enter() it might need to grab
+	 * the uring_lock to make progress. If we hold it here across the drain
+	 * wait, then we can deadlock. It's safe to drop the mutex here, since
+	 * no new references will come in after we've killed the percpu ref.
+	 */
+	mutex_unlock(&ctx->uring_lock);
 	wait_for_completion(&ctx->ctx_done);
+	mutex_lock(&ctx->uring_lock);
 
 	switch (opcode) {
 	case IORING_REGISTER_BUFFERS: