>> At boot time, probe function of multiple connected devices >> (proprietary devices) execute simultaneously. > >What exactly do you mean here? How can probe happen "simultaneously"? >The USB core prevents this, right? I have observed two scenarios to call probe function: Scenario #1: Driver inserted and attaching USB Device: Yes, you are right, two probes at same time is not happening in this scenario. Scenario #2: USB Device attached and inserting Driver: In this case probe has been called in context of insmod, refer following code flow: init -> usb_register_driver -> driver_register -> bus_add_driver -> driver_attach -> bus_for_each_dev -> __driver_attach -> driver_probe_device -> usb_probe_interface -> probe -> usb_register_dev I have observed the crash in Scenario #2, as two probes executes at same time in this scenario. And init_usb_class_mutex lock require to prevent race condition. >> And because of the following code path race condition happens: >> probe->usb_register_dev->init_usb_class > >Why is this just showing up now, and hasn't been an issue for the decade >or so this code has been around? What changed? > >> Tested with these changes, and problem has been solved. > >What changes? Tested with my patch (i.e. locking with init_usb_class_mutex). thanks, ajay kaher --------- Original Message --------- Sender : gregkh@xxxxxxxxxxxxxxxxxxx <gregkh@xxxxxxxxxxxxxxxxxxx> Date : 2017-01-31 12:31 (GMT+5:30) Title : Re: Re: Subject: [PATCH v1] USB:Core: BugFix: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously A: http://en.wikipedia.org/wiki/Top_post Q: Were do I find info about this thing called top-posting? A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail? A: No. Q: Should I include quotations after my reply? http://daringfireball.net/2007/07/on_top On Tue, Jan 31, 2017 at 05:21:46AM +0000, Ajay Kaher wrote: > > > At boot time, probe function of multiple connected devices > (proprietary devices) execute simultaneously. What exactly do you mean here? How can probe happen "simultaneously"? The USB core prevents this, right? And what do you mean exactly by "(proprietary devices)"? > And because of the following code path race condition happens: > probe->usb_register_dev->init_usb_class Why is this just showing up now, and hasn't been an issue for the decade or so this code has been around? What changed? > Tested with these changes, and problem has been solved. What changes? thanks, greg k-h Thanks and Regards, Ajay Kaher
