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Subject[PATCH v3 2/2] io_uring: off timeouts based only on completions
Date
Offset timeouts wait not for sqe->off non-timeout CQEs, but rather
sqe->off + number of prior inflight requests. Wait exactly for
sqe->off non-timeout completions

Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/io_uring.c | 65 +++++++++++----------------------------------------
1 file changed, 14 insertions(+), 51 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0975cd8ddcb7..732ec73ec3c0 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -394,7 +394,8 @@ struct io_timeout {
struct file *file;
u64 addr;
int flags;
- u32 count;
+ u32 off;
+ u32 target_seq;
};

struct io_rw {
@@ -1124,8 +1125,10 @@ static void io_flush_timeouts(struct io_ring_ctx *ctx)

if (req->flags & REQ_F_TIMEOUT_NOSEQ)
break;
- if (__req_need_defer(req))
+ if (req->timeout.target_seq != ctx->cached_cq_tail
+ - atomic_read(&ctx->cq_timeouts))
break;
+
list_del_init(&req->list);
io_kill_timeout(req);
}
@@ -4660,20 +4663,8 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer)
* We could be racing with timeout deletion. If the list is empty,
* then timeout lookup already found it and will be handling it.
*/
- if (!list_empty(&req->list)) {
- struct io_kiocb *prev;
-
- /*
- * Adjust the reqs sequence before the current one because it
- * will consume a slot in the cq_ring and the cq_tail
- * pointer will be increased, otherwise other timeout reqs may
- * return in advance without waiting for enough wait_nr.
- */
- prev = req;
- list_for_each_entry_continue_reverse(prev, &ctx->timeout_list, list)
- prev->sequence++;
+ if (!list_empty(&req->list))
list_del_init(&req->list);
- }

io_cqring_fill_event(req, -ETIME);
io_commit_cqring(ctx);
@@ -4765,7 +4756,7 @@ static int io_timeout_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe,
if (flags & ~IORING_TIMEOUT_ABS)
return -EINVAL;

- req->timeout.count = off;
+ req->timeout.off = off;

if (!req->io && io_alloc_async_ctx(req))
return -ENOMEM;
@@ -4789,13 +4780,10 @@ static int io_timeout_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe,
static int io_timeout(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
- struct io_timeout_data *data;
+ struct io_timeout_data *data = &req->io->timeout;
struct list_head *entry;
- unsigned span = 0;
- u32 count = req->timeout.count;
- u32 seq = req->sequence;
+ u32 tail, off = req->timeout.off;

- data = &req->io->timeout;
spin_lock_irq(&ctx->completion_lock);

/*
@@ -4803,13 +4791,14 @@ static int io_timeout(struct io_kiocb *req)
* timeout event to be satisfied. If it isn't set, then this is
* a pure timeout request, sequence isn't used.
*/
- if (!count) {
+ if (!off) {
req->flags |= REQ_F_TIMEOUT_NOSEQ;
entry = ctx->timeout_list.prev;
goto add;
}

- req->sequence = seq + count;
+ tail = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);
+ req->timeout.target_seq = tail + off;

/*
* Insertion sort, ensuring the first entry in the list is always
@@ -4817,39 +4806,13 @@ static int io_timeout(struct io_kiocb *req)
*/
list_for_each_prev(entry, &ctx->timeout_list) {
struct io_kiocb *nxt = list_entry(entry, struct io_kiocb, list);
- unsigned nxt_seq;
- long long tmp, tmp_nxt;
- u32 nxt_offset = nxt->timeout.count;

if (nxt->flags & REQ_F_TIMEOUT_NOSEQ)
continue;
-
- /*
- * Since seq + count can overflow, use type long
- * long to store it.
- */
- tmp = (long long)seq + count;
- nxt_seq = nxt->sequence - nxt_offset;
- tmp_nxt = (long long)nxt_seq + nxt_offset;
-
- /*
- * cached_sq_head may overflow, and it will never overflow twice
- * once there is some timeout req still be valid.
- */
- if (seq < nxt_seq)
- tmp += UINT_MAX;
-
- if (tmp > tmp_nxt)
+ /* nxt.seq is behind @tail, otherwise would've been completed */
+ if (off >= nxt->timeout.target_seq - tail)
break;
-
- /*
- * Sequence of reqs after the insert one and itself should
- * be adjusted because each timeout req consumes a slot.
- */
- span++;
- nxt->sequence++;
}
- req->sequence -= span;
add:
list_add(&req->list, entry);
data->timer.function = io_timeout_fn;
--
2.24.0
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