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Commit 5da0fb1a authored by yangerkun's avatar yangerkun Committed by Jens Axboe
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io_uring: consider the overflow of sequence for timeout req 



Now we recalculate the sequence of timeout with 'req->sequence =
ctx->cached_sq_head + count - 1', judge the right place to insert
for timeout_list by compare the number of request we still expected for
completion. But we have not consider about the situation of overflow:

1. ctx->cached_sq_head + count - 1 may overflow. And a bigger count for
the new timeout req can have a small req->sequence.

2. cached_sq_head of now may overflow compare with before req. And it
will lead the timeout req with small req->sequence.

This overflow will lead to the misorder of timeout_list, which can lead
to the wrong order of the completion of timeout_list. Fix it by reuse
req->submit.sequence to store the count, and change the logic of
inserting sort in io_timeout.

Signed-off-by: default avataryangerkun <yangerkun@huawei.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 7a7c5e71

fs/io_uring.c

+21 −6
Original line number Diff line number Diff line
@@ -1884,7 +1884,7 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer) 


static int io_timeout(struct io_kiocb *req, const struct io_uring_sqe *sqe)

{

	unsigned count, req_dist, tail_index;

	unsigned count;

	struct io_ring_ctx *ctx = req->ctx;

	struct list_head *entry;

	struct timespec64 ts;
@@ -1907,21 +1907,36 @@ static int io_timeout(struct io_kiocb *req, const struct io_uring_sqe *sqe) 
		count = 1;



	req->sequence = ctx->cached_sq_head + count - 1;

	/* reuse it to store the count */

	req->submit.sequence = count;

	req->flags |= REQ_F_TIMEOUT;



	/*

	 * Insertion sort, ensuring the first entry in the list is always

	 * the one we need first.

	 */

	tail_index = ctx->cached_cq_tail - ctx->rings->sq_dropped;

	req_dist = req->sequence - tail_index;

	spin_lock_irq(&ctx->completion_lock);

	list_for_each_prev(entry, &ctx->timeout_list) {

		struct io_kiocb *nxt = list_entry(entry, struct io_kiocb, list);

		unsigned dist;

		unsigned nxt_sq_head;

		long long tmp, tmp_nxt;



		dist = nxt->sequence - tail_index;

		if (req_dist >= dist)

		/*

		 * Since cached_sq_head + count - 1 can overflow, use type long

		 * long to store it.

		 */

		tmp = (long long)ctx->cached_sq_head + count - 1;

		nxt_sq_head = nxt->sequence - nxt->submit.sequence + 1;

		tmp_nxt = (long long)nxt_sq_head + nxt->submit.sequence - 1;



		/*

		 * cached_sq_head may overflow, and it will never overflow twice

		 * once there is some timeout req still be valid.

		 */

		if (ctx->cached_sq_head < nxt_sq_head)

			tmp_nxt += UINT_MAX;



		if (tmp >= tmp_nxt)

			break;

	}

	list_add(&req->list, entry);