Re: [PATCH] io_uring: reset -EBUSY error when io sq thread is waken up

Xiaoguang Wang
2020-05-20T13:16:45Z

hi,

> On 5/19/20 10:40 PM, Xiaoguang Wang wrote:
>> In io_sq_thread(), currently if we get an -EBUSY error, we will
>> won't clear it again, which will result in io_sq_thread() will
>> never have a chance to submit sqes again. Below test program test.c
>> can reveal this bug:
>>
>> int main(int argc, char *argv[])
>> {
>> struct io_uring ring;
>> int i, fd, ret;
>> struct io_uring_sqe *sqe;
>> struct io_uring_cqe *cqe;
>> struct iovec *iovecs;
>> void *buf;
>> struct io_uring_params p;
>>
>> if (argc < 2) {
>> printf("%s: file\n", argv[0]);
>> return 1;
>> }
>>
>> memset(&p, 0, sizeof(p));
>> p.flags = IORING_SETUP_SQPOLL;
>> ret = io_uring_queue_init_params(4, &ring, &p);
>> if (ret < 0) {
>> fprintf(stderr, "queue_init: %s\n", strerror(-ret));
>> return 1;
>> }
>>
>> fd = open(argv[1], O_RDONLY | O_DIRECT);
>> if (fd < 0) {
>> perror("open");
>> return 1;
>> }
>>
>> iovecs = calloc(10, sizeof(struct iovec));
>> for (i = 0; i < 10; i++) {
>> if (posix_memalign(&buf, 4096, 4096))
>> return 1;
>> iovecs[i].iov_base = buf;
>> iovecs[i].iov_len = 4096;
>> }
>>
>> ret = io_uring_register_files(&ring, &fd, 1);
>> if (ret < 0) {
>> fprintf(stderr, "%s: register %d\n", __FUNCTION__, ret);
>> return ret;
>> }
>>
>> for (i = 0; i < 10; i++) {
>> sqe = io_uring_get_sqe(&ring);
>> if (!sqe)
>> break;
>>
>> io_uring_prep_readv(sqe, 0, &iovecs[i], 1, 0);
>> sqe->flags |= IOSQE_FIXED_FILE;
>>
>> ret = io_uring_submit(&ring);
>> sleep(1);
>> printf("submit %d\n", i);
>> }
>>
>> for (i = 0; i < 10; i++) {
>> io_uring_wait_cqe(&ring, &cqe);
>> printf("receive: %d\n", i);
>> if (cqe->res != 4096) {
>> fprintf(stderr, "ret=%d, wanted 4096\n", cqe->res);
>> ret = 1;
>> }
>> io_uring_cqe_seen(&ring, cqe);
>> }
>>
>> close(fd);
>> io_uring_queue_exit(&ring);
>> return 0;
>> }
>> sudo ./test testfile
>> above command will hang on the tenth request, to fix this bug, when io
>> sq_thread is waken up, we reset the variable 'ret' to be zero.
>>
>> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
>> ---
>> fs/io_uring.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 6e51140a5722..747de5cdf38a 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -6045,6 +6045,8 @@ static int io_sq_thread(void *data)
>> finish_wait(&ctx->sqo_wait, &wait);
>>
>> ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
>> + if (ret == -EBUSY)
>> + ret = 0;
>> continue;
>> }
>> finish_wait(&ctx->sqo_wait, &wait);
>
> How about just unconditionally clearing it? There's nothing we
> need to preserve at this point, it should just get set to zero
> regardless of the value.
OK, agree, will send a new version soon, thanks.

Regards,
Xiaoguang Wang
>