Date: Wed, 21 Dec 2011 13:29:49 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: Hans Petter Selasky <hselasky@c2i.net> Cc: FreeBSD current <freebsd-current@FreeBSD.org>, "freebsd-usb@FreeBSD.org" <freebsd-usb@FreeBSD.org> Subject: Re: a few usb issues related to edge cases Message-ID: <4EF1C32D.3070107@FreeBSD.org> In-Reply-To: <4EF07EB0.9000209@FreeBSD.org> References: <4EEF2B11.6080802@FreeBSD.org> <201112191530.40526.hselasky@c2i.net> <4EF07EB0.9000209@FreeBSD.org>
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on 20/12/2011 14:25 Andriy Gapon said the following: > I just wanted to draw your attention to the fact that obtaining any locks in the > kdb context (or USB polling code in general, even) is not a good idea. > Chances of getting into trouble on those locks are probably quite moderate or > even low, but they do exist. I am not sure if you are getting any bug reports > about such troubles :-) Regular users probably do not use kdb too often and a > panic for them is just a "crash", so they likely do not expect anything > usable/debuggable after that :-) Looking some more at the code I just got myself confused as to how the dumping to a umass device could work when the scheduler is stopped. It seems that the umass_command_start -> usbd_transfer_start -> usbd_callback_ss_done_defer functions would always put a transfer request onto a queue and try to wake up a thread to process that queue and the request. But that's obviously not going to work when the other thread is not going to be run. Have I missed a code path that leads directly to the controller in this context? Thank you for your help. -- Andriy Gapon
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