From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 06EA2C54EBC for ; Tue, 10 Jan 2023 18:03:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231236AbjAJSDs (ORCPT ); Tue, 10 Jan 2023 13:03:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45478 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238177AbjAJSDV (ORCPT ); Tue, 10 Jan 2023 13:03:21 -0500 Received: from mail-pg1-x531.google.com (mail-pg1-x531.google.com [IPv6:2607:f8b0:4864:20::531]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4A8A99FD5 for ; Tue, 10 Jan 2023 10:01:02 -0800 (PST) Received: by mail-pg1-x531.google.com with SMTP id 7so8793962pga.1 for ; Tue, 10 Jan 2023 10:01:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20210112.gappssmtp.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=yQjfdBAuI+lCVIhAS7ja+ercSmY/+2TyjJmiFgzuNZM=; b=ehO+pW7c9jcZ5X0YHTx2bs3lN8BdFLqIHPcguf/KQk/WuFg8QWIOjQma+kQAR7ImI8 PbZPlRCqAKEFMxxew+pVxfmpE7IlOReCc5w90lTBYp2O0baHYRWV6uEDzeMNuD2xLbzg ZkrkKxK8aOaSRUqkZ0eI577Hfo8R17hm612IhzR2XxW835I19vkblL7zHNDL+IIZAq4+ jB1NNlpuJ7QXeefjDPJtbSQ0yvrpcmogqLIJqMHhiwBnPaK5ykGROLHFHnBxeJ+DU7Cg QkUHqgdQ3/JuSaENOGDQKeb0fhF7/9UoYxPBWajcBKlAe7AAPgUpWf9FcEsCmqEUfXnv oshg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=yQjfdBAuI+lCVIhAS7ja+ercSmY/+2TyjJmiFgzuNZM=; b=FQRrvhZzIPLYQNQE2dzH2OyxehU7z4pfCCmwb1qBMYKjOcs8LBVLMOdvFcxOHPEk/g LsrITGCCpx6PQFghqW/clQPho5TIGETAAIR90QEnNOtcJhRE+kYnMZ5dT3/kfJvSWQbY Lz6HYbS/JbQpXGJLCFkpGhlp9ecgvn0xdX9uV/xLYbcCi2p75NUNr7oPeDx4rkzYboq0 eZFs4U9fOTvDi47QmFfk459kF1Rh2S8rpcOr46oA/QyqA+0xye7e36S2gx8fSCNXIlBp QvFAihL2d5ZvRmL96F3htfzfn3J80xW2yRN7QzrnDtlqztmDJbOjYnu6qy0G1b4a/yYU T7Ag== X-Gm-Message-State: AFqh2kpnnmnCh70TfKLBqpmKHcP6/E/9+DUwqHZY72FNA3v4oOTYadEm 7GmWLpHEN7Pbn71qgjVFYh0yP81rME75r17X X-Google-Smtp-Source: AMrXdXsbK7c7PFA8/80nEZD8iBW5Lp052SkcqSmIAqs7oKHwM2X4HItK1ULxy9XA5m2d5r127W6RnA== X-Received: by 2002:a62:1695:0:b0:57f:f570:128d with SMTP id 143-20020a621695000000b0057ff570128dmr17615137pfw.1.1673373661385; Tue, 10 Jan 2023 10:01:01 -0800 (PST) Received: from localhost.localdomain ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id i24-20020a056a00225800b00583698ba91dsm8405877pfu.40.2023.01.10.10.01.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Jan 2023 10:01:00 -0800 (PST) From: Jens Axboe To: io-uring@vger.kernel.org Cc: asml.silence@gmail.com, Jens Axboe Subject: [PATCH 2/2] io_uring/poll: attempt request issue after racy poll wakeup Date: Tue, 10 Jan 2023 11:00:55 -0700 Message-Id: <20230110180055.204657-3-axboe@kernel.dk> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20230110180055.204657-1-axboe@kernel.dk> References: <20230110180055.204657-1-axboe@kernel.dk> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org If we have multiple requests waiting on the same target poll waitqueue, then it's quite possible to get a request triggered and get disappointed in not being able to make any progress with it. If we race in doing so, we'll potentially leave the poll request on the internal tables, but removed from the waitqueue. That means that any subsequent trigger of the poll waitqueue will not kick that request into action, causing an application to potentially wait for completion of a request that will never happen. Fix this by adding a new poll return state, IOU_POLL_REISSUE. Rather than have complicated logic for how to re-arm a given type of request, just punt it for a reissue. While in there, move the 'ret' variable to the only section where it gets used. This avoids confusion the scope of it. Fixes: 49f1c68e048f ("io_uring: optimise submission side poll_refs") Signed-off-by: Jens Axboe --- io_uring/poll.c | 30 +++++++++++++++++++----------- 1 file changed, 19 insertions(+), 11 deletions(-) diff --git a/io_uring/poll.c b/io_uring/poll.c index cf6a70bd54e0..0aca4ee6142b 100644 --- a/io_uring/poll.c +++ b/io_uring/poll.c @@ -223,21 +223,22 @@ enum { IOU_POLL_DONE = 0, IOU_POLL_NO_ACTION = 1, IOU_POLL_REMOVE_POLL_USE_RES = 2, + IOU_POLL_REISSUE = 3, }; /* * All poll tw should go through this. Checks for poll events, manages * references, does rewait, etc. * - * Returns a negative error on failure. IOU_POLL_NO_ACTION when no action require, - * which is either spurious wakeup or multishot CQE is served. - * IOU_POLL_DONE when it's done with the request, then the mask is stored in req->cqe.res. - * IOU_POLL_REMOVE_POLL_USE_RES indicates to remove multishot poll and that the result - * is stored in req->cqe. + * Returns a negative error on failure. IOU_POLL_NO_ACTION when no action + * require, which is either spurious wakeup or multishot CQE is served. + * IOU_POLL_DONE when it's done with the request, then the mask is stored in + * req->cqe.res. IOU_POLL_REMOVE_POLL_USE_RES indicates to remove multishot + * poll and that the result is stored in req->cqe. */ static int io_poll_check_events(struct io_kiocb *req, bool *locked) { - int v, ret; + int v; /* req->task == current here, checking PF_EXITING is safe */ if (unlikely(req->task->flags & PF_EXITING)) @@ -276,10 +277,15 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked) if (!req->cqe.res) { struct poll_table_struct pt = { ._key = req->apoll_events }; req->cqe.res = vfs_poll(req->file, &pt) & req->apoll_events; + /* + * We got woken with a mask, but someone else got to + * it first. The above vfs_poll() doesn't add us back + * to the waitqueue, so if we get nothing back, we + * should be safe and attempt a reissue. + */ + if ((unlikely(!req->cqe.res))) + return IOU_POLL_REISSUE; } - - if ((unlikely(!req->cqe.res))) - continue; if (req->apoll_events & EPOLLONESHOT) return IOU_POLL_DONE; @@ -294,7 +300,7 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked) return IOU_POLL_REMOVE_POLL_USE_RES; } } else { - ret = io_poll_issue(req, locked); + int ret = io_poll_issue(req, locked); if (ret == IOU_STOP_MULTISHOT) return IOU_POLL_REMOVE_POLL_USE_RES; if (ret < 0) @@ -330,6 +336,8 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked) poll = io_kiocb_to_cmd(req, struct io_poll); req->cqe.res = mangle_poll(req->cqe.res & poll->events); + } else if (ret == IOU_POLL_REISSUE) { + io_req_task_submit(req, locked); } else if (ret != IOU_POLL_REMOVE_POLL_USE_RES) { req->cqe.res = ret; req_set_fail(req); @@ -342,7 +350,7 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked) if (ret == IOU_POLL_REMOVE_POLL_USE_RES) io_req_task_complete(req, locked); - else if (ret == IOU_POLL_DONE) + else if (ret == IOU_POLL_DONE || ret == IOU_POLL_REISSUE) io_req_task_submit(req, locked); else io_req_defer_failed(req, ret); -- 2.39.0