io_uring: get rid of double locking

We don't need to take both uring_locks at once, msg_ring can be split in
two parts, first getting a file from the filetable of the first ring and
then installing it into the second one.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/a80ecc2bc99c3b3f2cf20015d618b7c51419a797.1670384893.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index c7d6586..387c45a 100644 (file)
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -15,6 +15,7 @@
 
 struct io_msg {
        struct file                     *file;
+       struct file                     *src_file;
        u64 user_data;
        u32 len;
        u32 cmd;
@@ -23,6 +24,17 @@ struct io_msg {
        u32 flags;
 };
 
+void io_msg_ring_cleanup(struct io_kiocb *req)
+{
+       struct io_msg *msg = io_kiocb_to_cmd(req, struct io_msg);
+
+       if (WARN_ON_ONCE(!msg->src_file))
+               return;
+
+       fput(msg->src_file);
+       msg->src_file = NULL;
+}
+
 static int io_msg_ring_data(struct io_kiocb *req)
 {
        struct io_ring_ctx *target_ctx = req->file->private_data;
@@ -37,17 +49,13 @@ static int io_msg_ring_data(struct io_kiocb *req)
        return -EOVERFLOW;
 }
 
-static void io_double_unlock_ctx(struct io_ring_ctx *ctx,
-                                struct io_ring_ctx *octx,
+static void io_double_unlock_ctx(struct io_ring_ctx *octx,
                                 unsigned int issue_flags)
 {
-       if (issue_flags & IO_URING_F_UNLOCKED)
-               mutex_unlock(&ctx->uring_lock);
        mutex_unlock(&octx->uring_lock);
 }
 
-static int io_double_lock_ctx(struct io_ring_ctx *ctx,
-                             struct io_ring_ctx *octx,
+static int io_double_lock_ctx(struct io_ring_ctx *octx,
                              unsigned int issue_flags)
 {
        /*
@@ -60,17 +68,28 @@ static int io_double_lock_ctx(struct io_ring_ctx *ctx,
                        return -EAGAIN;
                return 0;
        }
+       mutex_lock(&octx->uring_lock);
+       return 0;
+}
 
-       /* Always grab smallest value ctx first. We know ctx != octx. */
-       if (ctx < octx) {
-               mutex_lock(&ctx->uring_lock);
-               mutex_lock(&octx->uring_lock);
-       } else {
-               mutex_lock(&octx->uring_lock);
-               mutex_lock(&ctx->uring_lock);
+static struct file *io_msg_grab_file(struct io_kiocb *req, unsigned int issue_flags)
+{
+       struct io_msg *msg = io_kiocb_to_cmd(req, struct io_msg);
+       struct io_ring_ctx *ctx = req->ctx;
+       struct file *file = NULL;
+       unsigned long file_ptr;
+       int idx = msg->src_fd;
+
+       io_ring_submit_lock(ctx, issue_flags);
+       if (likely(idx < ctx->nr_user_files)) {
+               idx = array_index_nospec(idx, ctx->nr_user_files);
+               file_ptr = io_fixed_file_slot(&ctx->file_table, idx)->file_ptr;
+               file = (struct file *) (file_ptr & FFS_MASK);
+               if (file)
+                       get_file(file);
        }
-
-       return 0;
+       io_ring_submit_unlock(ctx, issue_flags);
+       return file;
 }
 
 static int io_msg_send_fd(struct io_kiocb *req, unsigned int issue_flags)
@@ -78,34 +97,27 @@ static int io_msg_send_fd(struct io_kiocb *req, unsigned int issue_flags)
        struct io_ring_ctx *target_ctx = req->file->private_data;
        struct io_msg *msg = io_kiocb_to_cmd(req, struct io_msg);
        struct io_ring_ctx *ctx = req->ctx;
-       unsigned long file_ptr;
-       struct file *src_file;
+       struct file *src_file = msg->src_file;
        int ret;
 
        if (target_ctx == ctx)
                return -EINVAL;
+       if (!src_file) {
+               src_file = io_msg_grab_file(req, issue_flags);
+               if (!src_file)
+                       return -EBADF;
+               msg->src_file = src_file;
+               req->flags |= REQ_F_NEED_CLEANUP;
+       }
 
-       ret = io_double_lock_ctx(ctx, target_ctx, issue_flags);
-       if (unlikely(ret))
-               return ret;
-
-       ret = -EBADF;
-       if (unlikely(msg->src_fd >= ctx->nr_user_files))
-               goto out_unlock;
-
-       msg->src_fd = array_index_nospec(msg->src_fd, ctx->nr_user_files);
-       file_ptr = io_fixed_file_slot(&ctx->file_table, msg->src_fd)->file_ptr;
-       if (!file_ptr)
-               goto out_unlock;
-
-       src_file = (struct file *) (file_ptr & FFS_MASK);
-       get_file(src_file);
+       if (unlikely(io_double_lock_ctx(target_ctx, issue_flags)))
+               return -EAGAIN;
 
        ret = __io_fixed_fd_install(target_ctx, src_file, msg->dst_fd);
-       if (ret < 0) {
-               fput(src_file);
+       if (ret < 0)
                goto out_unlock;
-       }
+       msg->src_file = NULL;
+       req->flags &= ~REQ_F_NEED_CLEANUP;
 
        if (msg->flags & IORING_MSG_RING_CQE_SKIP)
                goto out_unlock;
@@ -119,7 +131,7 @@ static int io_msg_send_fd(struct io_kiocb *req, unsigned int issue_flags)
        if (!io_post_aux_cqe(target_ctx, msg->user_data, msg->len, 0))
                ret = -EOVERFLOW;
 out_unlock:
-       io_double_unlock_ctx(ctx, target_ctx, issue_flags);
+       io_double_unlock_ctx(target_ctx, issue_flags);
        return ret;
 }
 
@@ -130,6 +142,7 @@ int io_msg_ring_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
        if (unlikely(sqe->buf_index || sqe->personality))
                return -EINVAL;
 
+       msg->src_file = NULL;
        msg->user_data = READ_ONCE(sqe->off);
        msg->len = READ_ONCE(sqe->len);
        msg->cmd = READ_ONCE(sqe->addr);

diff --git a/io_uring/msg_ring.h b/io_uring/msg_ring.h
index fb9601f..3987ee6 100644 (file)
--- a/io_uring/msg_ring.h
+++ b/io_uring/msg_ring.h
@@ -2,3 +2,4 @@
 
 int io_msg_ring_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_msg_ring(struct io_kiocb *req, unsigned int issue_flags);
+void io_msg_ring_cleanup(struct io_kiocb *req);

diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index 04dd2c9..3aa0d65 100644 (file)
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -445,6 +445,7 @@ const struct io_op_def io_op_defs[] = {
                .name                   = "MSG_RING",
                .prep                   = io_msg_ring_prep,
                .issue                  = io_msg_ring,
+               .cleanup                = io_msg_ring_cleanup,
        },
        [IORING_OP_FSETXATTR] = {
                .needs_file = 1,