On 3/17/24 8:47 PM, Ming Lei wrote: > On Sun, Mar 17, 2024 at 08:40:59PM -0600, Jens Axboe wrote: >> On 3/17/24 8:32 PM, Pavel Begunkov wrote: >>> On 3/18/24 02:25, Jens Axboe wrote: >>>> On 3/17/24 8:23 PM, Ming Lei wrote: >>>>> On Mon, Mar 18, 2024 at 12:41:47AM +0000, Pavel Begunkov wrote: >>>>>> !IO_URING_F_UNLOCKED does not translate to availability of the deferred >>>>>> completion infra, IO_URING_F_COMPLETE_DEFER does, that what we should >>>>>> pass and look for to use io_req_complete_defer() and other variants. >>>>>> >>>>>> Luckily, it's not a real problem as two wrongs actually made it right, >>>>>> at least as far as io_uring_cmd_work() goes. >>>>>> >>>>>> Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx> >>>>>> Link: https://lore.kernel.org/r/eb08e72e837106963bc7bc7dccfd93d646cc7f36.1710514702.git.asml.silence@xxxxxxxxx >>>>>> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> >>> >>> oops, I should've removed all the signed-offs >>> >>>>>> --- >>>>>> io_uring/uring_cmd.c | 10 ++++++++-- >>>>>> 1 file changed, 8 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c >>>>>> index f197e8c22965..ec38a8d4836d 100644 >>>>>> --- a/io_uring/uring_cmd.c >>>>>> +++ b/io_uring/uring_cmd.c >>>>>> @@ -56,7 +56,11 @@ EXPORT_SYMBOL_GPL(io_uring_cmd_mark_cancelable); >>>>>> static void io_uring_cmd_work(struct io_kiocb *req, struct io_tw_state *ts) >>>>>> { >>>>>> struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd); >>>>>> - unsigned issue_flags = ts->locked ? 0 : IO_URING_F_UNLOCKED; >>>>>> + unsigned issue_flags = IO_URING_F_UNLOCKED; >>>>>> + >>>>>> + /* locked task_work executor checks the deffered list completion */ >>>>>> + if (ts->locked) >>>>>> + issue_flags = IO_URING_F_COMPLETE_DEFER; >>>>>> ioucmd->task_work_cb(ioucmd, issue_flags); >>>>>> } >>>>>> @@ -100,7 +104,9 @@ void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, ssize_t res2, >>>>>> if (req->ctx->flags & IORING_SETUP_IOPOLL) { >>>>>> /* order with io_iopoll_req_issued() checking ->iopoll_complete */ >>>>>> smp_store_release(&req->iopoll_completed, 1); >>>>>> - } else if (!(issue_flags & IO_URING_F_UNLOCKED)) { >>>>>> + } else if (issue_flags & IO_URING_F_COMPLETE_DEFER) { >>>>>> + if (WARN_ON_ONCE(issue_flags & IO_URING_F_UNLOCKED)) >>>>>> + return; >>>>>> io_req_complete_defer(req); >>>>>> } else { >>>>>> req->io_task_work.func = io_req_task_complete; >>>>> >>>>> 'git-bisect' shows the reported warning starts from this patch. >>> >>> Thanks Ming >>> >>>> >>>> That does make sense, as probably: >>>> >>>> + /* locked task_work executor checks the deffered list completion */ >>>> + if (ts->locked) >>>> + issue_flags = IO_URING_F_COMPLETE_DEFER; >>>> >>>> this assumption isn't true, and that would mess with the task management >>>> (which is in your oops). >>> >>> I'm missing it, how it's not true? >>> >>> >>> static void ctx_flush_and_put(struct io_ring_ctx *ctx, struct io_tw_state *ts) >>> { >>> ... >>> if (ts->locked) { >>> io_submit_flush_completions(ctx); >>> ... >>> } >>> } >>> >>> static __cold void io_fallback_req_func(struct work_struct *work) >>> { >>> ... >>> mutex_lock(&ctx->uring_lock); >>> llist_for_each_entry_safe(req, tmp, node, io_task_work.node) >>> req->io_task_work.func(req, &ts); >>> io_submit_flush_completions(ctx); >>> mutex_unlock(&ctx->uring_lock); >>> ... >>> } >> >> I took a look too, and don't immediately see it. Those are also the two >> only cases I found, and before the patches, looks fine too. >> >> So no immediate answer there... But I can confirm that before this >> patch, test passes fine. With the patch, it goes boom pretty quick. >> Either directly off putting the task, or an unrelated memory crash >> instead. > > In ublk, the translated 'issue_flags' is passed to io_uring_cmd_done() > from ioucmd->task_work_cb()(__ublk_rq_task_work()). That might be > related with the reason. Or maybe ublk is doing multiple invocations of task_work completions? I added this: diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index a2cb8da3cc33..ba7641b380a9 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -739,6 +739,7 @@ static void io_put_task_remote(struct task_struct *task) { struct io_uring_task *tctx = task->io_uring; + WARN_ON_ONCE(!percpu_counter_read(&tctx->inflight)); percpu_counter_sub(&tctx->inflight, 1); if (unlikely(atomic_read(&tctx->in_cancel))) wake_up(&tctx->wait); and hit this: [ 77.386845] ------------[ cut here ]------------ [ 77.387128] WARNING: CPU: 5 PID: 109 at io_uring/io_uring.c:742 io_put_task_remote+0x164/0x1a8 [ 77.387608] Modules linked in: [ 77.387784] CPU: 5 PID: 109 Comm: kworker/5:1 Not tainted 6.8.0-11436-g340741d86a53-dirty #5750 [ 77.388277] Hardware name: linux,dummy-virt (DT) [ 77.388601] Workqueue: events io_fallback_req_func [ 77.388930] pstate: 81400005 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) [ 77.389402] pc : io_put_task_remote+0x164/0x1a8 [ 77.389711] lr : __io_submit_flush_completions+0x8b8/0x1308 [ 77.390087] sp : ffff800087327a60 [ 77.390317] x29: ffff800087327a60 x28: 1fffe0002040b329 x27: 1fffe0002040b32f [ 77.390817] x26: ffff000103c4e900 x25: ffff000102059900 x24: ffff000104670000 [ 77.391314] x23: ffff0000d2195000 x22: 00000000002ce20c x21: ffff0000ced4fcc8 [ 77.391787] x20: ffff0000ced4fc00 x19: ffff000103c4e900 x18: 0000000000000000 [ 77.392209] x17: ffff8000814b0c34 x16: ffff8000814affac x15: ffff8000814ac4a8 [ 77.392633] x14: ffff80008069327c x13: ffff800080018c9c x12: ffff600020789d26 [ 77.393055] x11: 1fffe00020789d25 x10: ffff600020789d25 x9 : dfff800000000000 [ 77.393479] x8 : 00009fffdf8762db x7 : ffff000103c4e92b x6 : 0000000000000001 [ 77.393904] x5 : ffff000103c4e928 x4 : ffff600020789d26 x3 : 1fffe0001a432a7a [ 77.394334] x2 : 1fffe00019da9f9a x1 : 0000000000000000 x0 : 0000000000000000 [ 77.394761] Call trace: [ 77.394913] io_put_task_remote+0x164/0x1a8 [ 77.395168] __io_submit_flush_completions+0x8b8/0x1308 [ 77.395481] io_fallback_req_func+0x138/0x1e8 [ 77.395742] process_one_work+0x538/0x1048 [ 77.395992] worker_thread+0x760/0xbd4 [ 77.396221] kthread+0x2dc/0x368 [ 77.396417] ret_from_fork+0x10/0x20 [ 77.396634] ---[ end trace 0000000000000000 ]--- [ 77.397706] ------------[ cut here ]------------ which is showing either an imbalance in the task references, or multiple completions from the same io_uring request. Anyway, I'll pop back in tomrrow, but hopefully the above is somewhat useful at least. I'd suspect the __ublk_rq_task_work() abort check for current != ubq->ubq_daemon and what happens off that. -- Jens Axboe
