[PATCH 7/7] io_uring: only publish fully handled mem region

[Pavel Begunkov <asml.silence@gmail.com>]

io_register_mem_region() can try to remove a region right after
publishing it. This non-atomicity is annoying. Do it in two steps
similar to io_register_mem_region(), create memory first and publish it
once the rest of the handling is done. Remove now unused
io_create_region_mmap_safe(), which was assumed to be a temporary
solution from day one.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/memmap.c   | 21 ---------------------
 io_uring/memmap.h   | 12 ++++++++++++
 io_uring/register.c | 11 ++++++-----
 3 files changed, 18 insertions(+), 26 deletions(-)

diff --git a/io_uring/memmap.c b/io_uring/memmap.c
index 2e99dffddfc5..aa388ecd4754 100644
--- a/io_uring/memmap.c
+++ b/io_uring/memmap.c
@@ -234,27 +234,6 @@ int io_create_region(struct io_ring_ctx *ctx, struct io_mapped_region *mr,
 	return ret;
 }
 
-int io_create_region_mmap_safe(struct io_ring_ctx *ctx, struct io_mapped_region *mr,
-				struct io_uring_region_desc *reg,
-				unsigned long mmap_offset)
-{
-	struct io_mapped_region tmp_mr;
-	int ret;
-
-	memcpy(&tmp_mr, mr, sizeof(tmp_mr));
-	ret = io_create_region(ctx, &tmp_mr, reg, mmap_offset);
-	if (ret)
-		return ret;
-
-	/*
-	 * Once published mmap can find it without holding only the ->mmap_lock
-	 * and not ->uring_lock.
-	 */
-	guard(mutex)(&ctx->mmap_lock);
-	memcpy(mr, &tmp_mr, sizeof(tmp_mr));
-	return 0;
-}
-
 static struct io_mapped_region *io_mmap_get_region(struct io_ring_ctx *ctx,
 						   loff_t pgoff)
 {
diff --git a/io_uring/memmap.h b/io_uring/memmap.h
index 08419684e4bc..58002976e0c3 100644
--- a/io_uring/memmap.h
+++ b/io_uring/memmap.h
@@ -36,4 +36,16 @@ static inline bool io_region_is_set(struct io_mapped_region *mr)
 	return !!mr->nr_pages;
 }
 
+static inline void io_region_publish(struct io_ring_ctx *ctx,
+				     struct io_mapped_region *src_region,
+				     struct io_mapped_region *dst_region)
+{
+	/*
+	 * Once published mmap can find it without holding only the ->mmap_lock
+	 * and not ->uring_lock.
+	 */
+	guard(mutex)(&ctx->mmap_lock);
+	*dst_region = *src_region;
+}
+
 #endif
diff --git a/io_uring/register.c b/io_uring/register.c
index b11550ed940c..43eb02004824 100644
--- a/io_uring/register.c
+++ b/io_uring/register.c
@@ -576,6 +576,7 @@ static int io_register_mem_region(struct io_ring_ctx *ctx, void __user *uarg)
 	struct io_uring_mem_region_reg reg;
 	struct io_uring_region_desc __user *rd_uptr;
 	struct io_uring_region_desc rd;
+	struct io_mapped_region region = {};
 	int ret;
 
 	if (io_region_is_set(&ctx->param_region))
@@ -599,20 +600,20 @@ static int io_register_mem_region(struct io_ring_ctx *ctx, void __user *uarg)
 	    !(ctx->flags & IORING_SETUP_R_DISABLED))
 		return -EINVAL;
 
-	ret = io_create_region_mmap_safe(ctx, &ctx->param_region, &rd,
-					 IORING_MAP_OFF_PARAM_REGION);
+	ret = io_create_region(ctx, &region, &rd, IORING_MAP_OFF_PARAM_REGION);
 	if (ret)
 		return ret;
 	if (copy_to_user(rd_uptr, &rd, sizeof(rd))) {
-		guard(mutex)(&ctx->mmap_lock);
-		io_free_region(ctx, &ctx->param_region);
+		io_free_region(ctx, &region);
 		return -EFAULT;
 	}
 
 	if (reg.flags & IORING_MEM_REGION_REG_WAIT_ARG) {
-		ctx->cq_wait_arg = io_region_get_ptr(&ctx->param_region);
+		ctx->cq_wait_arg = io_region_get_ptr(&region);
 		ctx->cq_wait_size = rd.size;
 	}
+
+	io_region_publish(ctx, &region, &ctx->param_region);
 	return 0;
 }
 
-- 
2.49.0