On 2019/10/16 9:45, Jens Axboe wrote:
On 10/15/19 7:35 PM, yangerkun wrote:
On 2019/10/15 21:59, yangerkun wrote:
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@xxxxxxxxxx>
---
fs/io_uring.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 76fdbe84aff5..c9512da06973 100644
--- 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;
Maybe there is a mistake, it should be tmp. So sorry about this.
I ran it through the basic testing, but I guess it doesn't catch overflow
cases. Maybe we can come up with one? Should be pretty simple to setup a
io_uring, post UINT_MAX - 10 nops (or something like that), then do some
timeout testing.
Good idea! I will try to add a testcase for this in liburing.
Just send an incremental patch to fix it.
OK, will send the fix patch!
