On Sat, Jan 02, 2021 at 08:26:26PM +0000, Pavel Begunkov wrote: > On 02/01/2021 19:54, Pavel Begunkov wrote: > > On 19/12/2020 19:15, 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 starting value of ->cached_cq_overflow - > >> ->cq_timeouts instead of the target value, so that we can safely > >> (without overflow problems) compare the number of events that have > >> happened with the number of events needed to trigger the timeout. > > https://www.spinics.net/lists/kernel/msg3475160.html > > The idea was to replace u32 cached_cq_tail with u64 while keeping > timeout offsets u32. Assuming that we won't ever hit ~2^62 inflight > requests, complete all requests falling into some large enough window > behind that u64 cached_cq_tail. > > simplifying: > > i64 d = target_off - ctx->u64_cq_tail > if (d <= 0 && d > -2^32) > complete_it() > > Not fond of it, but at least worked at that time. You can try out > this approach if you want, but would be perfect if you would find > something more elegant :) > What do you think about something like this? I think it's not totally correct because it relies on having ->completion_lock in io_timeout() so that ->cq_last_tm_flushed is updated, but in case of IORING_SETUP_IOPOLL, io_iopoll_complete() doesn't take that lock, and ->uring_lock will not be held if io_timeout() is called from io_wq_submit_work(), but maybe could still be worth it since that was already possibly a problem? diff --git a/fs/io_uring.c b/fs/io_uring.c index cb57e0360fcb..50984709879c 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -353,6 +353,7 @@ 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; @@ -1633,19 +1634,26 @@ static void __io_queue_deferred(struct io_ring_ctx *ctx) static void io_flush_timeouts(struct io_ring_ctx *ctx) { + u32 seq = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts); + while (!list_empty(&ctx->timeout_list)) { + u32 events_needed, events_got; struct io_kiocb *req = list_first_entry(&ctx->timeout_list, struct io_kiocb, timeout.list); if (io_is_timeout_noseq(req)) break; - if (req->timeout.target_seq != ctx->cached_cq_tail - - atomic_read(&ctx->cq_timeouts)) + + events_needed = req->timeout.target_seq - ctx->cq_last_tm_flush; + events_got = seq - ctx->cq_last_tm_flush; + if (events_got < events_needed) break; list_del_init(&req->timeout.list); io_kill_timeout(req); } + + ctx->cq_last_tm_flush = seq; } static void io_commit_cqring(struct io_ring_ctx *ctx) -- 2.20.1 > >> > >> Signed-off-by: Marcelo Diop-Gonzalez <marcelo827@xxxxxxxxx> > >> --- > >> fs/io_uring.c | 30 +++++++++++++++++++++++------- > >> 1 file changed, 23 insertions(+), 7 deletions(-) > >> > >> diff --git a/fs/io_uring.c b/fs/io_uring.c > >> index f394bf358022..f62de0cb5fc4 100644 > >> --- a/fs/io_uring.c > >> +++ b/fs/io_uring.c > >> @@ -444,7 +444,7 @@ struct io_cancel { > >> struct io_timeout { > >> struct file *file; > >> u32 off; > >> - u32 target_seq; > >> + u32 start_seq; > >> struct list_head list; > >> /* head of the link, used by linked timeouts only */ > >> struct io_kiocb *head; > >> @@ -1629,6 +1629,24 @@ static void __io_queue_deferred(struct io_ring_ctx *ctx) > >> } while (!list_empty(&ctx->defer_list)); > >> } > >> > >> +static inline u32 io_timeout_events_left(struct io_kiocb *req) > >> +{ > >> + struct io_ring_ctx *ctx = req->ctx; > >> + u32 events; > >> + > >> + /* > >> + * events -= req->timeout.start_seq and the comparison between > >> + * ->timeout.off and events will not overflow because each time > >> + * ->cq_timeouts is incremented, ->cached_cq_tail is incremented too. > >> + */ > >> + > >> + events = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts); > >> + events -= req->timeout.start_seq; > > > > It looks to me that events before the start_seq subtraction can have got wrapped > > around start_seq. > > > > e.g. > > 1) you submit a timeout with off=0xff...ff (start_seq=0 for convenience) > > > > 2) some time has passed, let @events = 0xff..ff - 1 > > so the timeout still waits > > > > 3) we commit 5 requests at once and call io_commit_cqring() only once for > > them, so we get @events == 0xff..ff - 1 + 5, i.e. 4 > > > > @events == 4 < off == 0xff...ff, > > so we didn't trigger out timeout even though should have > > > >> + if (req->timeout.off > events) > >> + return req->timeout.off - events; > >> + return 0; > >> +} > >> + > >> static void io_flush_timeouts(struct io_ring_ctx *ctx) > >> { > >> while (!list_empty(&ctx->timeout_list)) { > >> @@ -1637,8 +1655,7 @@ static void io_flush_timeouts(struct io_ring_ctx *ctx) > >> > >> if (io_is_timeout_noseq(req)) > >> break; > >> - if (req->timeout.target_seq != ctx->cached_cq_tail > >> - - atomic_read(&ctx->cq_timeouts)) > >> + if (io_timeout_events_left(req) > 0) > >> break; > >> > >> list_del_init(&req->timeout.list); > >> @@ -5785,7 +5802,6 @@ static int io_timeout(struct io_kiocb *req) > >> struct io_ring_ctx *ctx = req->ctx; > >> struct io_timeout_data *data = req->async_data; > >> struct list_head *entry; > >> - u32 tail, off = req->timeout.off; > >> > >> spin_lock_irq(&ctx->completion_lock); > >> > >> @@ -5799,8 +5815,8 @@ static int io_timeout(struct io_kiocb *req) > >> goto add; > >> } > >> > >> - tail = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts); > >> - req->timeout.target_seq = tail + off; > >> + req->timeout.start_seq = ctx->cached_cq_tail - > >> + atomic_read(&ctx->cq_timeouts); > >> > >> /* > >> * Insertion sort, ensuring the first entry in the list is always > >> @@ -5813,7 +5829,7 @@ static int io_timeout(struct io_kiocb *req) > >> if (io_is_timeout_noseq(nxt)) > >> continue; > >> /* nxt.seq is behind @tail, otherwise would've been completed */ > >> - if (off >= nxt->timeout.target_seq - tail) > >> + if (req->timeout.off >= io_timeout_events_left(nxt)) > >> break; > >> } > >> add: > >> > > > > -- > Pavel Begunkov
