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[65.112.8.54]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-50939e8e14esm36187391cf.6.2026.03.12.10.56.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Mar 2026 10:56:57 -0700 (PDT) Date: Thu, 12 Mar 2026 13:56:55 -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: <76ea1412-ee4d-4eaf-b8a8-5866ad960b52@rowland.harvard.edu> References: <497b1bab-984c-43d7-9ef0-6614d2c1b426@rowland.harvard.edu> <69b1c190.a00a0220.707e5.0002.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: <69b1c190.a00a0220.707e5.0002.GAE@google.com> On Wed, Mar 11, 2026 at 12:25:04PM -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 The console log contains some very strange looking stuff. I need more debugging info. 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 +460,28 @@ static void set_link_state(struct dummy_ unsigned int reset = USB_PORT_STAT_RESET & (~dum_hcd->old_status) & dum_hcd->port_status; + if (reset) + dev_info(&dum->gadget.dev, "Dummy %p reset, ints_enabled %d\n", dum, 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 A\n", dum->callback_usage); 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 A\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 B\n", dum->callback_usage); spin_unlock(&dum->lock); if (dum_hcd->old_active && dum->driver->suspend) dum->driver->suspend(&dum->gadget); @@ -482,6 +489,7 @@ 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 B\n", dum->callback_usage); } dum_hcd->old_status = dum_hcd->port_status; @@ -908,21 +916,6 @@ 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 +938,27 @@ static void dummy_udc_async_callbacks(st spin_lock_irq(&dum->lock); dum->ints_enabled = enable; + dev_info(&_gadget->dev, "Dummy %p ints_enabled <- %d A\n", dum, 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 %p ints_enabled = %d !\n", dum, dum->ints_enabled); + } spin_unlock_irq(&dum->lock); } @@ -1020,6 +1034,8 @@ 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 +1048,7 @@ static int dummy_udc_stop(struct usb_gad spin_lock_irq(&dum->lock); dum->ints_enabled = 0; + dev_info(&g->dev, "Dummy %p ints_enabled <- %d B\n", dum, dum->ints_enabled); stop_activity(dum); dum->driver = NULL; spin_unlock_irq(&dum->lock); @@ -1923,11 +1940,13 @@ restart: */ if (value > 0) { ++dum->callback_usage; + dev_info(&dum->gadget.dev, "Inc usage: %d C\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 C\n", dum->callback_usage); if (value >= 0) { /* no delays (max 64KB data stage) */