From: Benjamin Herrenschmidt benh@kernel.crashing.org
[ Upstream commit 4a56a478a525d6427be90753451c40e1327caa1a ]
If fsg_disable() and fsg_set_alt() are called too closely to each other (for example due to a quick reset/reconnect), what can happen is that fsg_set_alt sets common->new_fsg from an interrupt while handle_exception is trying to process the config change caused by fsg_disable():
fsg_disable() ... handle_exception() sets state back to FSG_STATE_NORMAL hasn't yet called do_set_interface() or is inside it.
---> interrupt fsg_set_alt sets common->new_fsg queues a new FSG_STATE_CONFIG_CHANGE <---
Now, the first handle_exception can "see" the updated new_fsg, treats it as if it was a fsg_set_alt() response, call usb_composite_setup_continue() etc...
But then, the thread sees the second FSG_STATE_CONFIG_CHANGE, and goes back down the same path, wipes and reattaches a now active fsg, and .. calls usb_composite_setup_continue() which at this point is wrong.
Not only we get a backtrace, but I suspect the second set_interface wrecks some state causing the host to get upset in my case.
This fixes it by replacing "new_fsg" by a "state argument" (same principle) which is set in the same lock section as the state update, and retrieved similarly.
That way, there is never any discrepancy between the dequeued state and the observed value of it. We keep the ability to have the latest reconfig operation take precedence, but we guarantee that once "dequeued" the argument (new_fsg) will not be clobbered by any new event.
Signed-off-by: Benjamin Herrenschmidt benh@kernel.crashing.org Acked-by: Alan Stern stern@rowland.harvard.edu Signed-off-by: Felipe Balbi felipe.balbi@linux.intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/usb/gadget/function/f_mass_storage.c | 28 +++++++++++++------- 1 file changed, 18 insertions(+), 10 deletions(-)
diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c index 043f97ad8f226..f2bc8d0370676 100644 --- a/drivers/usb/gadget/function/f_mass_storage.c +++ b/drivers/usb/gadget/function/f_mass_storage.c @@ -261,7 +261,7 @@ struct fsg_common; struct fsg_common { struct usb_gadget *gadget; struct usb_composite_dev *cdev; - struct fsg_dev *fsg, *new_fsg; + struct fsg_dev *fsg; wait_queue_head_t io_wait; wait_queue_head_t fsg_wait;
@@ -290,6 +290,7 @@ struct fsg_common { unsigned int bulk_out_maxpacket; enum fsg_state state; /* For exception handling */ unsigned int exception_req_tag; + void *exception_arg;
enum data_direction data_dir; u32 data_size; @@ -391,7 +392,8 @@ static int fsg_set_halt(struct fsg_dev *fsg, struct usb_ep *ep)
/* These routines may be called in process context or in_irq */
-static void raise_exception(struct fsg_common *common, enum fsg_state new_state) +static void __raise_exception(struct fsg_common *common, enum fsg_state new_state, + void *arg) { unsigned long flags;
@@ -404,6 +406,7 @@ static void raise_exception(struct fsg_common *common, enum fsg_state new_state) if (common->state <= new_state) { common->exception_req_tag = common->ep0_req_tag; common->state = new_state; + common->exception_arg = arg; if (common->thread_task) send_sig_info(SIGUSR1, SEND_SIG_PRIV, common->thread_task); @@ -411,6 +414,10 @@ static void raise_exception(struct fsg_common *common, enum fsg_state new_state) spin_unlock_irqrestore(&common->lock, flags); }
+static void raise_exception(struct fsg_common *common, enum fsg_state new_state) +{ + __raise_exception(common, new_state, NULL); +}
/*-------------------------------------------------------------------------*/
@@ -2285,16 +2292,16 @@ static int do_set_interface(struct fsg_common *common, struct fsg_dev *new_fsg) static int fsg_set_alt(struct usb_function *f, unsigned intf, unsigned alt) { struct fsg_dev *fsg = fsg_from_func(f); - fsg->common->new_fsg = fsg; - raise_exception(fsg->common, FSG_STATE_CONFIG_CHANGE); + + __raise_exception(fsg->common, FSG_STATE_CONFIG_CHANGE, fsg); return USB_GADGET_DELAYED_STATUS; }
static void fsg_disable(struct usb_function *f) { struct fsg_dev *fsg = fsg_from_func(f); - fsg->common->new_fsg = NULL; - raise_exception(fsg->common, FSG_STATE_CONFIG_CHANGE); + + __raise_exception(fsg->common, FSG_STATE_CONFIG_CHANGE, NULL); }
@@ -2307,6 +2314,7 @@ static void handle_exception(struct fsg_common *common) enum fsg_state old_state; struct fsg_lun *curlun; unsigned int exception_req_tag; + struct fsg_dev *new_fsg;
/* * Clear the existing signals. Anything but SIGUSR1 is converted @@ -2360,6 +2368,7 @@ static void handle_exception(struct fsg_common *common) common->next_buffhd_to_fill = &common->buffhds[0]; common->next_buffhd_to_drain = &common->buffhds[0]; exception_req_tag = common->exception_req_tag; + new_fsg = common->exception_arg; old_state = common->state; common->state = FSG_STATE_NORMAL;
@@ -2413,8 +2422,8 @@ static void handle_exception(struct fsg_common *common) break;
case FSG_STATE_CONFIG_CHANGE: - do_set_interface(common, common->new_fsg); - if (common->new_fsg) + do_set_interface(common, new_fsg); + if (new_fsg) usb_composite_setup_continue(common->cdev); break;
@@ -2989,8 +2998,7 @@ static void fsg_unbind(struct usb_configuration *c, struct usb_function *f)
DBG(fsg, "unbind\n"); if (fsg->common->fsg == fsg) { - fsg->common->new_fsg = NULL; - raise_exception(fsg->common, FSG_STATE_CONFIG_CHANGE); + __raise_exception(fsg->common, FSG_STATE_CONFIG_CHANGE, NULL); /* FIXME: make interruptible or killable somehow? */ wait_event(common->fsg_wait, common->fsg != fsg); }