Date: Tue, 30 Mar 2010 16:25:30 +0200 From: Attilio Rao <attilio@freebsd.org> To: Alexander Motin <mav@freebsd.org> Cc: freebsd-scsi@freebsd.org, "Justin T. Gibbs" <gibbs@freebsd.org>, mj@feral.com, Ed Maste <emaste@sandvine.com> Subject: Re: How is supposed to be protected the units list? Message-ID: <3bbf2fe11003300725vdb1e4ddrf112778ca2bbbc20@mail.gmail.com> In-Reply-To: <4BA5C746.7060203@FreeBSD.org> References: <3bbf2fe11002281655i61a5f0a0if3f381ad0c4a1ef8@mail.gmail.com> <3bbf2fe11003031547kd5f7314t3d83b2bde06c1c2f@mail.gmail.com> <4B8EF990.5030407@feral.com> <3bbf2fe11003031607wa3727b5ke89bc2a909d4d6a6@mail.gmail.com> <4B901419.8060800@feral.com> <3bbf2fe11003041737p30690522ya81e1b8f4bd6bbf9@mail.gmail.com> <3bbf2fe11003120601y3c403a1ct50f9fc6c1f0903bf@mail.gmail.com> <4B9A91DA.7030107@FreeBSD.org> <3bbf2fe11003200523t60895bfv1fa73d04e58a7838@mail.gmail.com> <4BA5C746.7060203@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
2010/3/21 Alexander Motin <mav@freebsd.org>: > Attilio Rao wrote: >> So I made this new patch using the bus lock: >> http://www.freebsd.org/~attilio/Sandvine/pdrv/xpt_lock.diff > > OK. I've looked on both and I think both have race window between unit > number allocation and insertion into the list. I've changed last patch > to not drop the lock in meantime. What do you think about this: > http://people.freebsd.org/~mav/unit_lock.patch > ? > > Part about scsi_da.c I don't like in both cases, as I am not sure that > locks can't be recursed there in case of some errors. I don't see how > adding second lock could solve it. The lock recursion is going to happen because of the necessary refcount acquisition as Matt pointed out? Or there is another recursion? In the former case, the global lock will help because you may just acquire it, refcount the periph, cache them and run lockless. You can't do this with xpt_lock_bus because of the recursion in cam_periph_acquire. So we want to live this unprotected and just live with this bug? Attilio -- Peace can only be achieved by understanding - A. Einstein
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3bbf2fe11003300725vdb1e4ddrf112778ca2bbbc20>