On 14/01/2021 15:50, Marcelo Diop-Gonzalez wrote:
> Right now io_flush_timeouts() checks if the current number of events
> is equal to ->timeout.target_seq, but this will miss some timeouts if
> there have been more than 1 event added since the last time they were
> flushed (possible in io_submit_flush_completions(), for example). Fix
> it by recording the last sequence at which timeouts were flushed so
> that the number of events seen can be compared to the number of events
> needed without overflow.
Looks good, but there is a little change I'll ask you to make (see
below). In a meanwhile I'll test it, so the patch on the fast track.
>
> Signed-off-by: Marcelo Diop-Gonzalez <marcelo827@xxxxxxxxx>
> ---
> fs/io_uring.c | 29 +++++++++++++++++++++++++----
> 1 file changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 372be9caf340..71d8fa0733ad 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -354,6 +354,7 @@ struct io_ring_ctx {
> unsigned cq_entries;
> unsigned cq_mask;
> atomic_t cq_timeouts;
> + unsigned cq_last_tm_flush;
> unsigned long cq_check_overflow;
> struct wait_queue_head cq_wait;
> struct fasync_struct *cq_fasync;
> @@ -1639,19 +1640,36 @@ static void __io_queue_deferred(struct io_ring_ctx *ctx)
>
> static void io_flush_timeouts(struct io_ring_ctx *ctx)
> {
> - while (!list_empty(&ctx->timeout_list)) {
> + u32 seq = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);
This assignment should go after list_empty() -- because of the atomic part
my compiler can't reshuffle them itself.
> +
> + if (list_empty(&ctx->timeout_list))
> + return;
[...]
> static void io_commit_cqring(struct io_ring_ctx *ctx)
> @@ -5837,6 +5855,9 @@ static int io_timeout(struct io_kiocb *req)
> tail = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);
> req->timeout.target_seq = tail + off;
>
> + /* Update the last seq here in case io_flush_timeouts() hasn't */
> + ctx->cq_last_tm_flush = tail;
Have to note that it's ok to do because we don't mix submissions and
completions, so io_timeout should never fall under same completion_lock
section as cq commit,
but otherwise some future locked version of io_timeout would be cutting
off a part of the current flush window (i.e. this [last, cur] thing).
--
Pavel Begunkov
