Hi Alan, W dniu 03.06.2014 16:48, Alan Stern pisze:
On Tue, 3 Jun 2014 Wei.Yang@xxxxxxxxxxxxx wrote:From: Yang Wei <Wei.Yang@xxxxxxxxxxxxx> While loading g_mass_storage module, the following warning is triggered. In fact, it is more easy to reproduce it with RT kernel. WARNING: at drivers/usb/gadget/composite.c: usb_composite_setup_continue: Unexpected call Modules linked in: fat vfat minix nls_cp437 nls_iso8859_1 g_mass_storage [<800179cc>] (unwind_backtrace+0x0/0x104) from [<80619608>] (dump_stack+0x20/0x24) [<80619608>] (dump_stack+0x20/0x24) from [<80025100>] (warn_slowpath_common+0x64/0x74) [<80025100>] (warn_slowpath_common+0x64/0x74) from [<800251cc>] (warn_slowpath_fmt+0x40/0x48) [<800251cc>] (warn_slowpath_fmt+0x40/0x48) from [<7f047774>] (usb_composite_setup_continue+0xb4/0xbc [g_mass_storage]) [<7f047774>] (usb_composite_setup_continue+0xb4/0xbc [g_mass_storage]) from [<7f047ad4>] (handle_exception+0x358/0x3e4 [g_mass_storage]) [<7f047ad4>] (handle_exception+0x358/0x3e4 [g_mass_storage]) from [<7f048080>] (fsg_main_thread+0x520/0x157c [g_mass_storage]) [<7f048080>] (fsg_main_thread+0x520/0x157c [g_mass_storage]) from [<8004bc90>] (kthread+0x98/0x9c) [<8004bc90>] (kthread+0x98/0x9c) from [<8000faec>] (kernel_thread_exit+0x0/0x8) The root cause just likes the following scenario. irq thread composite_disconnect() | |->fsg_disable() fsg->common->new_fsg = NULL and then wake fsg_main_thread with seting common->state to FSG_STATE_CONFIG_CHANGE. fsg_main_thread | |->do_set_interface() irq thread set_config() | |->fsg_set_alt() fsg->common->new_fsg = new_fsg and then also wake up fsg_main_thread with setting common->state to FSG_STATE_CONFIG_CHANGE. |-> if(common->new_fsg) usb_composite_setup_continue() In this case, fsg_main_thread would invoke usb_composite_setup_continue twice, so the second call would trigger the above call trace, as we also save common->new_fsg while changing the common->state.Michal and Andrzej: I haven't paid much attention to these matters, because you handled the conversion from g_file_storage to f_mass_storage using the composite framework. But this patch seemed odd, so I took a closer look.
Actually when I started dealing with usb gadgets the f_mass_storage had already been there. My involvement started with some cleanup, then moving to the new function registration interface (usb_get/put_function_instance(), usb_get/put_function()) and adding configfs support. That said, it is not impossible for me to have spoilt something :O
In f_mass_storage.c, struct fsg_common is shared among all the function instances. This structure includes things like cmnd and nluns, which will in general be different for different functions. That's okay if each function is in a separate config, but what happens when there are multiple functions in the same config, using different interfaces? What if the host sends concurrent commands to two of these functions?
When Sebastian introduced the function registration interface I didn't specially like the naming: struct usb_function_instance is something different than an instance of struct usb_function. The purpose of fsg_alloc_inst() is to create a usb_function_instance whose container_of is struct fsg_opts. In fact it is struct fsg_opts which is actually allocated; one of its members is struct fsg_common which is also allocated - individually for each struct usb_function_instance. Among traditional gadgets there is no gadget which uses mass storage function more than once. On the other hand, when gadgets are created with configfs it is forbidden to link a given function more than once into a given config, that is a struct usb_function_instance can be referenced by more than one config, but can be referenced only once in a given config; each symbolic link corresponds to an instance of struct usb_function (don't confuse with struct usb_function_instance). So yes, an fsg_common can be shared among instances of struct usb_function, but neither with traditional gadgets as they are now nor with configfs is it possible to have the same fsg_common referenced more than once in a given config. AP -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
