From: Alan Stern Date: Sun, 15 Mar 2026 18:31:00 +0000 (-0400) Subject: USB: dummy-hcd: Fix interrupt synchronization error X-Git-Tag: v7.0-rc7~10^2~31 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2ca9e46f8f1f5a297eb0ac83f79d35d5b3a02541;p=thirdparty%2Flinux.git USB: dummy-hcd: Fix interrupt synchronization error This fixes an error in synchronization in the dummy-hcd driver. The error has a somewhat involved history. The synchronization mechanism was introduced by commit 7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change"), which added an emulated "interrupts enabled" flag together with code emulating synchronize_irq() (it waits until all current handler callbacks have returned). But the emulated interrupt-disable occurred too late, after the driver containing the handler callback routines had been told that it was unbound and no more callbacks would occur. Commit 4a5d797a9f9c ("usb: gadget: dummy_hcd: fix gpf in gadget_setup") tried to fix this by moving the synchronize_irq() emulation code from dummy_stop() to dummy_pullup(), which runs before the unbind callback. There still were races, though, because the emulated interrupt-disable still occurred too late. It couldn't be moved to dummy_pullup(), because that routine can be called for reasons other than an impending unbind. Therefore commits 7dc0c55e9f30 ("USB: UDC core: Add udc_async_callbacks gadget op") and 04145a03db9d ("USB: UDC: Implement udc_async_callbacks in dummy-hcd") added an API allowing the UDC core to tell dummy-hcd exactly when emulated interrupts and their callbacks should be disabled. That brings us to the current state of things, which is still wrong because the emulated synchronize_irq() occurs before the emulated interrupt-disable! That's no good, beause it means that more emulated interrupts can occur after the synchronize_irq() emulation has run, leading to the possibility that a callback handler may be running when the gadget driver is unbound. To fix this, we have to move the synchronize_irq() emulation code yet again, to the dummy_udc_async_callbacks() routine, which takes care of enabling and disabling emulated interrupt requests. The synchronization will now run immediately after emulated interrupts are disabled, which is where it belongs. Signed-off-by: Alan Stern Fixes: 04145a03db9d ("USB: UDC: Implement udc_async_callbacks in dummy-hcd") Cc: stable Link: https://patch.msgid.link/c7bc93fe-4241-4d04-bd56-27c12ba35c97@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/usb/gadget/udc/dummy_hcd.c b/drivers/usb/gadget/udc/dummy_hcd.c index 860ee7d3ef98..e55701575857 100644 --- a/drivers/usb/gadget/udc/dummy_hcd.c +++ b/drivers/usb/gadget/udc/dummy_hcd.c @@ -913,21 +913,6 @@ static int dummy_pullup(struct usb_gadget *_gadget, int value) 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)); @@ -950,6 +935,20 @@ static void dummy_udc_async_callbacks(struct usb_gadget *_gadget, bool enable) spin_lock_irq(&dum->lock); dum->ints_enabled = enable; + if (!enable) { + /* + * Emulate synchronize_irq(): wait for callbacks to finish. + * This has to happen after emulated interrupts are disabled + * (dum->ints_enabled is clear) and before the unbind callback, + * just like the call to synchronize_irq() in + * gadget/udc/core:gadget_unbind_driver(). + */ + while (dum->callback_usage > 0) { + spin_unlock_irq(&dum->lock); + usleep_range(1000, 2000); + spin_lock_irq(&dum->lock); + } + } spin_unlock_irq(&dum->lock); }