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io_uring: consider the overflow of sequence for timeout req

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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>
This commit is contained in:
yangerkun 2019-10-15 21:59:29 +08:00 committed by Jens Axboe
parent 7a7c5e715e
commit 5da0fb1ab3
1 changed files with 21 additions and 6 deletions
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27
fs/io_uring.c
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@ -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);