Date: Tue, 12 Feb 2013 08:43:32 +0100 From: Hans Petter Selasky <hselasky@c2i.net> To: John Baldwin <jhb@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r246614 - head/sys/dev/usb/wlan Message-ID: <201302120843.32349.hselasky@c2i.net> In-Reply-To: <201302111133.02161.jhb@freebsd.org> References: <201302101036.r1AAaHs1022034@svn.freebsd.org> <201302111133.02161.jhb@freebsd.org>
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On Monday 11 February 2013 17:33:02 John Baldwin wrote: > On Sunday, February 10, 2013 5:36:17 am Hans Petter Selasky wrote: > > Author: hselasky > > Date: Sun Feb 10 10:36:16 2013 > > New Revision: 246614 > > URL: http://svnweb.freebsd.org/changeset/base/246614 > > > > Log: > > - Streamline detach logic in wlan drivers, so that > > > > freed memory cannot be used during detach. > > > > - Remove all panic() calls from the urtw driver because > > > > panic() is not appropriate here. > > > > - Remove redundant checks for device detached in > > > > device detach callbacks. > > > > - Use DEVMETHOD_END to mark end of device methods. > > Using a detached flag to bail from ioctl generally means you are doing > things wrong in detach. The correct solution is to always detach your > ifnet first, then start tearing down other state. In general with device > detach routines the first order of business is removing external > references such as character devices, ifnets, etc. and only start shutting > down the hardware and releasing state once those steps have completed. Hi, What I can do to solve the problem is to lock a mutex while detaching. Is the ifnet detach routine non-blocking? Why do I say that? It is because we are in a chicken-egg situation. USB is feeding data into ifnet and ifnet is feeding data into USB. Each stack is running under its own lock. The current approach is: 1) Stop data traffic in both directions 2) Make sure no more init happens (ioctl fix) 3) Free USB and IFNET. I see currently no way I can atomically stop all traffic and prevent futher init at the same time, while holding a single mutex. Do you? --HPS
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