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 X-Spam-Level: X-Spam-Status: No, score=-20.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35C1CC433E7 for ; Fri, 16 Oct 2020 13:57:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DA32C20848 for ; Fri, 16 Oct 2020 13:57:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Y4XB+ZRh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408169AbgJPN54 (ORCPT ); Fri, 16 Oct 2020 09:57:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2395556AbgJPN5z (ORCPT ); Fri, 16 Oct 2020 09:57:55 -0400 Received: from mail-wm1-x34a.google.com (mail-wm1-x34a.google.com [IPv6:2a00:1450:4864:20::34a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 889ABC061755 for ; Fri, 16 Oct 2020 06:57:55 -0700 (PDT) Received: by mail-wm1-x34a.google.com with SMTP id c204so811795wmd.5 for ; Fri, 16 Oct 2020 06:57:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=7zDNhPy5uc8ogz43uAAVw05Oz1rJmR7+6LDT853a82A=; b=Y4XB+ZRhrCz7A+n9G/WnCF8CEAVpPH07zo9bQCsffKeXsRpHkh4nYvpGW9+UdVYH9I 5ewSDjdF+a6y0YJNM7iMm9F/TQT9oox5ruhHmKebT//cZXOkVCuABfGe7UUFhYERSAPj hTfj5tqZ6X0TF9X/3PAcmBdgpOrga4CXpcq8tQybjN18LXGarSEWMwket6K8LvfkzhYf AceeBY45BtBzhysrUEXMvx7iHFIVsN1nmY8Lgv5lA/qBUXLiPvV0Nxe3Dk4yDBe1kZVQ BrUBWSyIHFKryNJhGizpiQn18nzMEVvoKxNPfYK6kGPqmNzlMLwGtVEw2FciLOe6+spk G1BA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=7zDNhPy5uc8ogz43uAAVw05Oz1rJmR7+6LDT853a82A=; b=jKLG00775bVHhiNqjf3mZhGEbX2OyQPDx6xIJRFETZC7Sagu3EJCLAc3YVown0lyp5 9Usha4HkDbnELDqTerPK6elC5czbhalE4cDRrpDFpuOsfPn/pUpwnqkKMAIJ/pB34wQF lc/U2KGALaj42rfKj4Dl4TSMHzu3gSA/E81si+bCyVyBLm3jH4ftVwkUiB8O4uatdP7H hiI11C4M69wUB74eMC/pFVPXwcYJFMj0Y+ABWL+hDzT2/KXPWM+fUZX1qKMPsa4Oy+Mj Jo47OS7VwsOchk454oVL8Nyq+T/eIvWd72Mpl9a919jH7u+4CcZapMs5Pq07Eq9bsLWZ pj3Q== X-Gm-Message-State: AOAM532lmSUNftPrAth2FNGmWZS4qiPAWGGr9okimB9iiaEn3stf8/Iy 9RHTgtfXk2ul7Fg3SanIhQ2Cs85SO4CnXPYX X-Google-Smtp-Source: ABdhPJyjpxbLtjDZsCgYCWCSKPekYZtidvLDRCAX+mRjETMl7mHYP/SGTA6yKCFT9+QDQLxxgZfWL5c6GwsXIZUW Sender: "andreyknvl via sendgmr" X-Received: from andreyknvl3.muc.corp.google.com ([2a00:79e0:15:13:7220:84ff:fe09:7e9d]) (user=andreyknvl job=sendgmr) by 2002:a1c:c28a:: with SMTP id s132mr3899832wmf.67.1602856673396; Fri, 16 Oct 2020 06:57:53 -0700 (PDT) Date: Fri, 16 Oct 2020 15:57:45 +0200 Message-Id: Mime-Version: 1.0 X-Mailer: git-send-email 2.29.0.rc1.297.gfa9743e501-goog Subject: [PATCH v4] kcov, usb: only collect coverage from __usb_hcd_giveback_urb in softirq From: Andrey Konovalov To: Dmitry Vyukov , Greg Kroah-Hartman Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Alan Stern , Shuah Khan , Alexander Potapenko , Marco Elver , Aleksandr Nogikh , Nazime Hande Harputluoglu , Andrey Konovalov Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Currently there's a KCOV remote coverage collection section in __usb_hcd_giveback_urb(). Initially that section was added based on the assumption that usb_hcd_giveback_urb() can only be called in interrupt context as indicated by a comment before it. This is what happens when syzkaller is fuzzing the USB stack via the dummy_hcd driver. As it turns out, it's actually valid to call usb_hcd_giveback_urb() in task context, provided that the caller turned off the interrupts; USB/IP does exactly that. This can lead to a nested KCOV remote coverage collection sections both trying to collect coverage in task context. This isn't supported by KCOV, and leads to a WARNING. Change __usb_hcd_giveback_urb() to only call kcov_remote_*() callbacks when it's being executed in a softirq. As the result, the coverage from USB/IP related usb_hcd_giveback_urb() calls won't be collected, but the WARNING is fixed. A potential future improvement would be to support nested remote coverage collection sections, but this patch doesn't address that. Signed-off-by: Andrey Konovalov Acked-by: Marco Elver --- Changes v3->v4: - Don't make any kcov changes, do a softirq context check in usb code instead. --- drivers/usb/core/hcd.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c index a33b849e8beb..2f6a39e09dc6 100644 --- a/drivers/usb/core/hcd.c +++ b/drivers/usb/core/hcd.c @@ -1646,9 +1646,16 @@ static void __usb_hcd_giveback_urb(struct urb *urb) /* pass ownership to the completion handler */ urb->status = status; - kcov_remote_start_usb((u64)urb->dev->bus->busnum); + /* + * This function can be called in task context inside another remote + * coverage collection section, but KCOV doesn't support that kind of + * recursion yet. Only collect coverage in softirq context for now. + */ + if (in_serving_softirq()) + kcov_remote_start_usb((u64)urb->dev->bus->busnum); urb->complete(urb); - kcov_remote_stop(); + if (in_serving_softirq()) + kcov_remote_stop(); usb_anchor_resume_wakeups(anchor); atomic_dec(&urb->use_count); -- 2.29.0.rc1.297.gfa9743e501-goog