From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qv1-f49.google.com (mail-qv1-f49.google.com [209.85.219.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A54F83BE626 for ; Fri, 13 Mar 2026 16:07:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.49 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773418030; cv=none; b=Y7TncO3dJIWRh3h2Er4UAUZXcgEGuFH0Kgg+YNvig5pTAwHaaKU+Lmk27uXEilXpTMOgU7pFhUxdu1xTmfQYUtdIBBt27LOZjjW+bquFldqMnMGdc5fEnENJ3rEK5hKZoD3+KDLYj/KyQngX0A+6/1p55bs56hCfKeMwal40u5M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773418030; c=relaxed/simple; bh=WqR3PYjk2uMZK/8W0O4eCFZt+kWfoSU+GZqz5IH08vg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=AJDm4AaF2kmm9+s4lGngAFaiQnW7moFqJnzmLqZamBSmFZ57G4WrKd16MXZluK7ti13E2MUugbrw7TRaLgU0PmFnj/j6y/zU7FBG0p0AZ8Vx/3c/y708FK1/u7Wjm6aO1jDklHiJCdGhf/EFd0LzNyWKjcVDlNVR4BjYYJmjoko= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=rowland.harvard.edu; spf=fail smtp.mailfrom=g.harvard.edu; dkim=pass (2048-bit key) header.d=rowland.harvard.edu header.i=@rowland.harvard.edu header.b=Nf3fpBlg; arc=none smtp.client-ip=209.85.219.49 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=rowland.harvard.edu Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=g.harvard.edu Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=rowland.harvard.edu header.i=@rowland.harvard.edu header.b="Nf3fpBlg" Received: by mail-qv1-f49.google.com with SMTP id 6a1803df08f44-89a0ece9f14so27860616d6.3 for ; Fri, 13 Mar 2026 09:07:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rowland.harvard.edu; s=google; t=1773418027; x=1774022827; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=+D12SmZC41fUm05hyWSOTm/E2HNan+11WhpBP9pVs+s=; b=Nf3fpBlg/nKvWn/Q3mGTGDErLIteyc0jctzMmUccsJv4xshkiHG+YBogVhSasROJYh h161IKHpsNb8vZ3QLUzMYrO6Xc+lH1YSxYMUB7UD2BHFKhaGFTUuRtWyDmrGvvj/fYvs 0Vu/SVld9dI818Z5+asmLrgL30kG+9ICAJLGOl2mGAzoTXr3SsGALuqcaxJqgrvgqgGf GuaOKRLhtcCGgEn2z7k+R0Yg3chd7YyA/z5RJ15Gw3ayNsI/9/vffHLRztxHUwJdyhJ1 Za5sqx+U5uvVTGFM0FWeaKjYgTz/KLbjO5pLQ0N3tSNH8S5SQE7QCjaX1Iumy5Sg0a46 3+og== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1773418027; x=1774022827; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=+D12SmZC41fUm05hyWSOTm/E2HNan+11WhpBP9pVs+s=; b=gWP1cYg277UBFK0astkUPHuk8JUYwb/lMnVmJ6pHFETeb+vpjC4puiT8+3C4+51p/p UDR5f+wQRF180KY9jFBq9s5FLtDOCQ3j5Dbui2t0qlIWKsmwBhavLptrHE7UCLa0OL9x +FckT2pa2hbvJY/FYQI2imcO72DDK+mg25Zd6x9l1OkLKVnV4z/wqhbQL3wlvtuUjdTo 8X1mizv+9bXuoPwaROppQGIfujYcWHbXYLDonARobRcZukU2KLLGbyibuVarv439nL6Z 4rPHU3BiLEok9oujlFTPB2P05aVcBzRsvDA7l6qygSOKX5Cxlvq9s+12lhZTD0AexsmZ +xbw== X-Forwarded-Encrypted: i=1; AJvYcCVeR6ScGqH2LQvGBwTgRI5BRl4bhcj8+59N4IyR1ofaBOOENwIL0RFce8DxAjp+kRP2dw3aTzaRWd48604=@vger.kernel.org X-Gm-Message-State: AOJu0YyDHFFWTZ4xYupTnMymcPugbH7sDUNGXkzNDqvUieMa1Uzp8PUs 3KHmaPlTYabOEg0E01KZnf9r+xQmm1Z4qkI2UVgosp4NXG0WRyWW+Hw4IF1TBRNAfw== X-Gm-Gg: ATEYQzwkqwTnJMKoZRCcNdNgy2stZ3mlYph4DQZpEqN916cwEx6tXpfy4ZjVHXeOj/Y jo+MzRSXbQXkEh8Pj/GtIlfQC8eVpJ9dyzXQPdPTLeEg8CiLKgLnV5SBb7A2LygzSJTNSbABoJH sEsqiAnQpFY6FwiAKWmCudVW9ncmBEwdqCzkW7O2WNVeSdlia2HvXOXJt/zFsfO/tiuo6eVULNp 9/7Lw+xCIFDBtAT5ZCu13tCxwE0IT9qoqvsx/Twmd6EHuVU4zwgKP5M71vg7iHXRn1R/cLweuQe by1uRoS6xQ4KOkYQ1npKkrGP5AvZeRDmTFX1P4G21xVVBuf1Xd2isCBTfBr4kxJu297JN6YHF3/ ZfggoPfWQHp5uN50TUeWJcohvW4v4X0bOWzW/H/Y222FXN3fUPnwbTP9DMSWHM8DkS2pDVwB2xv LejlhlwMEd0j3nFJjoLxsZS0r2 X-Received: by 2002:a05:6214:2b0f:b0:899:f741:5aea with SMTP id 6a1803df08f44-89a81d32831mr62349766d6.8.1773418027360; Fri, 13 Mar 2026 09:07:07 -0700 (PDT) Received: from rowland.harvard.edu ([2601:19b:d01:d210::687c]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-89a7995b712sm35071716d6.31.2026.03.13.09.07.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Mar 2026 09:07:06 -0700 (PDT) Date: Fri, 13 Mar 2026 12:07:04 -0400 From: Alan Stern To: syzbot Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [usb?] general protection fault in usb_gadget_udc_reset (4) Message-ID: References: <69b3797b.050a0220.36eb34.0006.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69b3797b.050a0220.36eb34.0006.GAE@google.com> On Thu, Mar 12, 2026 at 07:42:03PM -0700, syzbot wrote: > Hello, > > syzbot has tested the proposed patch but the reproducer is still triggering an issue: > general protection fault in usb_gadget_udc_reset > > raw-gadget.1 gadget.0: Dummy disconnect 0 reset 16, ints_enabled 1 > raw-gadget.1 gadget.0: Inc usage: 1 X > Oops: general protection fault, probably for non-canonical address 0xdffffc0000000008: 0000 [#1] SMP KASAN PTI I believe I have found the problem. The code in question in dummy_hcd.c does this: dev_info(&dum->gadget.dev, "Dummy disconnect %d reset %d, ints_enabled %d\n", disconnect, reset, dum->ints_enabled); /* Report reset and disconnect events to the driver */ if (dum->ints_enabled && (disconnect || reset)) { stop_activity(dum); ++dum->callback_usage; dev_info(&dum->gadget.dev, "Inc usage: %d X\n", dum->callback_usage); spin_unlock(&dum->lock); The issue is that dum->callback_usage needs to be incremented after the dum->ints_enabled check and before the dum->lock spinlock is released, but stop_activity() drops the spinlock temporarily while giving back cancelled requests. Let's interchange the increment and the stop_activity() call. That's the only change here from the prior test patch. Alan Stern #syz test: upstream 651690480a96 Index: usb-devel/drivers/usb/gadget/udc/dummy_hcd.c =================================================================== --- usb-devel.orig/drivers/usb/gadget/udc/dummy_hcd.c +++ usb-devel/drivers/usb/gadget/udc/dummy_hcd.c @@ -460,21 +460,27 @@ static void set_link_state(struct dummy_ unsigned int reset = USB_PORT_STAT_RESET & (~dum_hcd->old_status) & dum_hcd->port_status; + dev_info(&dum->gadget.dev, "Dummy disconnect %d reset %d, ints_enabled %d\n", disconnect, reset, dum->ints_enabled); + /* Report reset and disconnect events to the driver */ if (dum->ints_enabled && (disconnect || reset)) { - stop_activity(dum); ++dum->callback_usage; + dev_info(&dum->gadget.dev, "Inc usage: %d X\n", dum->callback_usage); + stop_activity(dum); spin_unlock(&dum->lock); + udelay(1000); if (reset) usb_gadget_udc_reset(&dum->gadget, dum->driver); else dum->driver->disconnect(&dum->gadget); spin_lock(&dum->lock); --dum->callback_usage; + dev_info(&dum->gadget.dev, "Dec usage: %d X\n", dum->callback_usage); } } else if (dum_hcd->active != dum_hcd->old_active && dum->ints_enabled) { ++dum->callback_usage; + dev_info(&dum->gadget.dev, "Inc usage: %d Y\n", dum->callback_usage); spin_unlock(&dum->lock); if (dum_hcd->old_active && dum->driver->suspend) dum->driver->suspend(&dum->gadget); @@ -482,6 +488,7 @@ static void set_link_state(struct dummy_ dum->driver->resume(&dum->gadget); spin_lock(&dum->lock); --dum->callback_usage; + dev_info(&dum->gadget.dev, "Dec usage: %d Y\n", dum->callback_usage); } dum_hcd->old_status = dum_hcd->port_status; @@ -908,21 +915,6 @@ static int dummy_pullup(struct usb_gadge spin_lock_irqsave(&dum->lock, flags); dum->pullup = (value != 0); set_link_state(dum_hcd); - if (value == 0) { - /* - * Emulate synchronize_irq(): wait for callbacks to finish. - * This seems to be the best place to emulate the call to - * synchronize_irq() that's in usb_gadget_remove_driver(). - * Doing it in dummy_udc_stop() would be too late since it - * is called after the unbind callback and unbind shouldn't - * be invoked until all the other callbacks are finished. - */ - while (dum->callback_usage > 0) { - spin_unlock_irqrestore(&dum->lock, flags); - usleep_range(1000, 2000); - spin_lock_irqsave(&dum->lock, flags); - } - } spin_unlock_irqrestore(&dum->lock, flags); usb_hcd_poll_rh_status(dummy_hcd_to_hcd(dum_hcd)); @@ -945,6 +937,27 @@ static void dummy_udc_async_callbacks(st spin_lock_irq(&dum->lock); dum->ints_enabled = enable; + dev_info(&_gadget->dev, "Dummy ints_enabled <- %d A\n", dum->ints_enabled); + if (!enable) { + dev_info(&dum->gadget.dev, "Wait usage %d\n", dum->callback_usage); + /* + * Emulate synchronize_irq(): wait for callbacks to finish. + * This seems to be the best place to emulate the call to + * synchronize_irq() that's in usb_gadget_remove_driver(). + * It has to come after dum->ints_enabled is clear. But + * doing it in dummy_udc_stop() would be too late since that + * routine is called after the unbind callback, and unbind + * shouldn't be invoked until all the other callbacks are + * finished. + */ + while (dum->callback_usage > 0) { + spin_unlock_irq(&dum->lock); + usleep_range(1000, 2000); + spin_lock_irq(&dum->lock); + } + if (dum->ints_enabled) + dev_info(&_gadget->dev, "Dummy ints_enabled = %d !\n", dum->ints_enabled); + } spin_unlock_irq(&dum->lock); } @@ -1020,6 +1033,8 @@ static int dummy_udc_start(struct usb_ga spin_lock_irq(&dum->lock); dum->devstatus = 0; dum->driver = driver; + dev_info(&dum->gadget.dev, "Start on bus %d\n", + dummy_hcd_to_hcd(dum_hcd)->self.busnum); spin_unlock_irq(&dum->lock); return 0; @@ -1032,6 +1047,7 @@ static int dummy_udc_stop(struct usb_gad spin_lock_irq(&dum->lock); dum->ints_enabled = 0; + dev_info(&g->dev, "Dummy ints_enabled <- %d B\n", dum->ints_enabled); stop_activity(dum); dum->driver = NULL; spin_unlock_irq(&dum->lock); @@ -1923,11 +1939,13 @@ restart: */ if (value > 0) { ++dum->callback_usage; + dev_info(&dum->gadget.dev, "Inc usage: %d Z\n", dum->callback_usage); spin_unlock(&dum->lock); value = dum->driver->setup(&dum->gadget, &setup); spin_lock(&dum->lock); --dum->callback_usage; + dev_info(&dum->gadget.dev, "Dec usage: %d Z\n", dum->callback_usage); if (value >= 0) { /* no delays (max 64KB data stage) */