Date: Wed, 21 Dec 2011 20:26:52 +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: <4EF224EC.9050101@FreeBSD.org> In-Reply-To: <201112211738.36126.hselasky@c2i.net> References: <4EEF2B11.6080802@FreeBSD.org> <4EF07EB0.9000209@FreeBSD.org> <4EF1C32D.3070107@FreeBSD.org> <201112211738.36126.hselasky@c2i.net>
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on 21/12/2011 18:38 Hans Petter Selasky said the following: > On Wednesday 21 December 2011 12:29:49 Andriy Gapon wrote: >> 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. > > Hi, > > Those threads should be polled when calling usbd_transfer_poll(). I.E. the > wakeup should be stubbed in the !scheduler_running case. Ah, that's what I missed! -- Andriy Gapon
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