76b61ebf1b
There's a failure case where an application gets a cqe entry, but
the kernel can then overwrite it before the application is done
reading it. This can happen since the io_uring_{get,wait}_completion()
interface both returns a CQE pointer AND increments the ring index.
If the kernel reuses this entry before the applications is done reading
it, the contents may be corrupted.
Remove the CQ head increment from the CQE retrieval, and put it into
a separate helper, io_uring_cqe_seen(). The application must call this
helper when it got a new CQE entry through one of the above calls, and
it's now done reading it.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
88 lines
1.4 KiB
C
88 lines
1.4 KiB
C
/*
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* Description: test CQ ring overflow
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*
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*/
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#include <errno.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <string.h>
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#include <fcntl.h>
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#include "../src/liburing.h"
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static int queue_n_nops(struct io_uring *ring, int n)
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{
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struct io_uring_sqe *sqe;
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int i, ret;
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for (i = 0; i < n; i++) {
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sqe = io_uring_get_sqe(ring);
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if (!sqe) {
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printf("get sqe failed\n");
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goto err;
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}
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io_uring_prep_nop(sqe);
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}
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ret = io_uring_submit(ring);
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if (ret < n) {
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printf("Submitted only %d\n", ret);
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goto err;
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} else if (ret < 0) {
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printf("sqe submit failed: %d\n", ret);
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goto err;
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}
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return 0;
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err:
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return 1;
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}
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int main(int argc, char *argv[])
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{
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struct io_uring_cqe *cqe;
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struct io_uring ring;
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int i, ret;
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ret = io_uring_queue_init(4, &ring, 0);
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if (ret) {
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printf("ring setup failed\n");
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return 1;
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}
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if (queue_n_nops(&ring, 4))
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goto err;
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if (queue_n_nops(&ring, 4))
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goto err;
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if (queue_n_nops(&ring, 4))
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goto err;
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i = 0;
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do {
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ret = io_uring_get_completion(&ring, &cqe);
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if (ret < 0) {
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printf("wait completion %d\n", ret);
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goto err;
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}
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io_uring_cqe_seen(&ring, cqe);
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if (!cqe)
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break;
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i++;
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} while (1);
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if (i != 8 || *ring.cq.koverflow != 4) {
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printf("CQ overflow fail: %d completions, %u overflow\n", i,
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*ring.cq.koverflow);
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goto err;
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}
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io_uring_queue_exit(&ring);
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return 0;
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err:
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io_uring_queue_exit(&ring);
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return 1;
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}
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