Date: Tue, 26 Apr 2011 16:42:17 +0200 From: Hans Petter Selasky <hselasky@c2i.net> To: freebsd-hackers@freebsd.org Cc: Bartosz Fabianowski <freebsd@chillt.de> Subject: Re: Is there some implicit locking of device methods? Message-ID: <201104261642.17569.hselasky@c2i.net> In-Reply-To: <201104261037.17893.jhb@freebsd.org> References: <4DB695DB.1080505@chillt.de> <5627117D-499B-4FD7-BF84-BE4BE6F583D7@bsdimp.com> <201104261037.17893.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tuesday 26 April 2011 16:37:17 John Baldwin wrote: > On Tuesday, April 26, 2011 10:27:14 am Warner Losh wrote: > > On Apr 26, 2011, at 7:42 AM, John Baldwin wrote: > > > - The Giant protection for new-bus should prevent attach/detach from > > > running > > > > > > concurrently I believe (either that or the USB bus itself should > > > ensure that the two instances of your device have seperate device_t > > > instances with separate softc's, so current attach/detach should not > > > matter except that they may both try to talk to the same hardware > > > perhaps? In that case that is something the USB bus driver should > > > fix by prevent a device from attaching at an existing address until > > > any existing device at that address is fully detached). > > > > I thought that if we held Giant when we're about to go to sleep that we > > drop it as a special case. So if any newbus-releated function sleeps, > > we can have a situation where attach is running and detach gets called. > > There is (or was) some code to cope with this in CardBus, iirc. I'm > > surprised there isn't any in USB, since Hans was the one that alerted me > > to this issue. > > Yes, Giant doesn't really provide too much help here. However, the real > fix should be in the USB bus, and USB peripheral drivers should not have > to worry about handling concurrent attach/detach (they can't really handle > it safely anyway). Hi, All detach/attach/suspend/resume functions on a device tree belonging to the same USB controller are executed from a single thread, which is called the root HUB thread. --HPS
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201104261642.17569.hselasky>