io_uring/napi: enable even with a timeout of 0

1 usec is not as short as it used to be, and it makes sense to allow 0
for a busy poll timeout - this means just do one loop to check if we
have anything available. Add a separate ->napi_enabled to check if napi
has been enabled or not.

While at it, move the writing of the ctx napi values after we've copied
the old values back to userspace. This ensures that if the call fails,
we'll be in the same state as we were before, rather than some
indeterminate state.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 4fe7af8a49078a83bdf253d4c9e821256c602a25..bd7071aeec5d016e1e4a02897c63d5cf816a0aac 100644 (file)
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -420,6 +420,7 @@ struct io_ring_ctx {
        /* napi busy poll default timeout */
        unsigned int            napi_busy_poll_to;
        bool                    napi_prefer_busy_poll;
+       bool                    napi_enabled;
 
        DECLARE_HASHTABLE(napi_ht, 4);
 #endif

diff --git a/io_uring/napi.c b/io_uring/napi.c
index b234adda7dfd2d49f5b673827c0764336602f0af..883a1a6659075604259f15265dd57096ebfe7536 100644 (file)
--- a/io_uring/napi.c
+++ b/io_uring/napi.c
@@ -227,12 +227,12 @@ int io_register_napi(struct io_ring_ctx *ctx, void __user *arg)
        if (napi.pad[0] || napi.pad[1] || napi.pad[2] || napi.resv)
                return -EINVAL;
 
-       WRITE_ONCE(ctx->napi_busy_poll_to, napi.busy_poll_to);
-       WRITE_ONCE(ctx->napi_prefer_busy_poll, !!napi.prefer_busy_poll);
-
        if (copy_to_user(arg, &curr, sizeof(curr)))
                return -EFAULT;
 
+       WRITE_ONCE(ctx->napi_busy_poll_to, napi.busy_poll_to);
+       WRITE_ONCE(ctx->napi_prefer_busy_poll, !!napi.prefer_busy_poll);
+       WRITE_ONCE(ctx->napi_enabled, true);
        return 0;
 }
 
@@ -256,6 +256,7 @@ int io_unregister_napi(struct io_ring_ctx *ctx, void __user *arg)
 
        WRITE_ONCE(ctx->napi_busy_poll_to, 0);
        WRITE_ONCE(ctx->napi_prefer_busy_poll, false);
+       WRITE_ONCE(ctx->napi_enabled, false);
        return 0;
 }
 
@@ -300,7 +301,7 @@ void __io_napi_busy_loop(struct io_ring_ctx *ctx, struct io_wait_queue *iowq)
 {
        iowq->napi_prefer_busy_poll = READ_ONCE(ctx->napi_prefer_busy_poll);
 
-       if (!(ctx->flags & IORING_SETUP_SQPOLL) && iowq->napi_busy_poll_to)
+       if (!(ctx->flags & IORING_SETUP_SQPOLL) && ctx->napi_enabled)
                io_napi_blocking_busy_loop(ctx, iowq);
 }