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: yangerkun <yangerkun@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 38d274f..d2cb277 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -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);