[PATCH AUTOSEL 5.6 20/47] io_uring: reset -EBUSY error when io sq thread is waken up

Sasha Levin
2020-05-28T11:56:51Z

From: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

[ Upstream commit d4ae271dfaae2a5f41c015f2f20d62a1deeec734 ]

In io_sq_thread(), currently if we get an -EBUSY error and go to sleep,
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.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/io_uring.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 504484dc33e4..c6e1f76a6ee0 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5224,6 +5224,7 @@ static int io_sq_thread(void *data)
finish_wait(&ctx->sqo_wait, &wait);

ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
+ ret = 0;
continue;
}
finish_wait(&ctx->sqo_wait, &wait);
--
2.25.1