Hi, I found two implementation details in t/io_uring.c quite interesting. Both are in the prep_more_ios() function. 1. reading the sq ring head is not protected using something like READ_ONCE() or smp_read_acquire(). According to https://www.kernel.org/doc/Documentation/memory-barriers.txt ``` It _must_not_ be assumed that the compiler will do what you want with memory references that are not protected by READ_ONCE() and WRITE_ONCE(). Without them, the compiler is within its rights to do all sorts of "creative" transformations, which are covered in the COMPILER BARRIER section. ``` Is it possible that the modifications to the sqe using init_io() get reordered prior to reading the sq ring head? 2. Writing to the sq ring tail is not protected using something like smp_store_release. Even according to the article "Efficient IO with io_uring", adding an sqe should be like: ``` write_barrier(); sqring->tail = tail; write_barrier(); ``` However, the first write barrier is missing in the t/io_uring.c Is it possible that the memory stores get reordered? Can anyone provide some insights on this? Thank you! Best, Hongwei
