Date: Tue, 9 Nov 2010 16:05:18 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Andriy Gapon <avg@freebsd.org> Cc: freebsd-x11@freebsd.org, freebsd-current@freebsd.org Subject: Re: radeon_cp_texture: page fault with non-sleepable locks held Message-ID: <20101109140518.GV2392@deviant.kiev.zoral.com.ua> In-Reply-To: <4CD9139D.9060302@freebsd.org> References: <4CD3B1D2.30003@icyb.net.ua> <4CD7E401.1010206@freebsd.org> <20101108120403.GC2392@deviant.kiev.zoral.com.ua> <4CD9139D.9060302@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
--gR2gBiFPsZkfqe6l Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Nov 09, 2010 at 11:25:49AM +0200, Andriy Gapon wrote: > on 08/11/2010 14:04 Kostik Belousov said the following: > > On Mon, Nov 08, 2010 at 01:50:25PM +0200, Andriy Gapon wrote: > >> on 05/11/2010 09:27 Andriy Gapon said the following: > >>> > >>> I use FreeSBD head and KDE 4 with all the bells and whistles enabled. > >>> Apparently recent KDE update has enabled even more of them, because I= started to > >>> have panics with a kernel that has INVARIANTS and WITNESS enabled. > >> > >> I tried to solve the problem by changing drmdev from mutex to sx: > >> http://people.freebsd.org/~avg/drm-sx.diff > > I remember that drm lock can be acquired from the interrupt thread, if > > the card supports interrupts. Changing it to sx cannot work then, becau= se > > interrupt threads cannot sleep. Most likely, you are getting around it > > since r600 not yet used interrupts on FreeBSD. > >=20 > > I think the solution is to drop drm lock around copyin. >=20 > Kostik, >=20 > I looked at this some more and now I think that using sx is a step in the= right > direction. >=20 > Rationale: > 1. it seems that on Linux mutex is a sleepable lock and thus can be safel= y held > across a page fault; and Linux mutex -> FreeBSD sx seems to be a porting > technique used for kernel code before[*]. > 2. DRM interrupt code uses a different lock - irq_lock, which is locked v= ia > DRM_SPINLOCK macro (expands to FreeBSD mutex); apparently even on Linux a "even on Linux". Heh. > sleep-able lock can't be acquired in interrupt handler. >=20 > I use Linux this and Linux that as a justification, because the DRM code > apparently originated with Linux model/idioms in mind, although the origi= nal > purpose was for the code to be portable. >=20 > So, what do you think about this aspect? > Should you agree with the usage of sx, then the previous question pops ba= ck - I do not agree. > how to resolve the lock order reversal between drmdev lock and user map l= ock > (which both would be sx). Easiest would be for DRM to provide wrappers for copyin/copyout that unlock, do operation and lock. Where is the reverse order (user map -> drm) ? >=20 > [*] http://www.ukuug.org/events/eurobsdcon2009/papers/dvb_driver_paper.pdf > --=20 > Andriy Gapon --gR2gBiFPsZkfqe6l Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAkzZVR0ACgkQC3+MBN1Mb4igNwCdGq0Gj0h8j/rE8m/9BH7vwc9c aecAoLzwf6qiJ7K+hLQeRQ0tAU2tYuJI =574k -----END PGP SIGNATURE----- --gR2gBiFPsZkfqe6l--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20101109140518.GV2392>