From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Anholt Subject: Re: [PATCH v7 4/4] drm/vc4: Allocate binner bo when starting to use the V3D Date: Thu, 02 May 2019 11:27:29 -0700 Message-ID: <87k1f8ww32.fsf@anholt.net> References: <20190425122917.26536-1-paul.kocialkowski@bootlin.com> <20190425122917.26536-5-paul.kocialkowski@bootlin.com> <87tvemj80z.fsf@anholt.net> <5d8dadb34c9f845e21349253ff21c036c417f37a.camel@bootlin.com> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha512; protocol="application/pgp-signature" Return-path: In-Reply-To: <5d8dadb34c9f845e21349253ff21c036c417f37a.camel@bootlin.com> Sender: linux-kernel-owner@vger.kernel.org To: Paul Kocialkowski , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: David Airlie , Daniel Vetter , Maxime Ripard , Eben Upton List-Id: dri-devel@lists.freedesktop.org --=-=-= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Paul Kocialkowski writes: > Hi, > > On Thu, 2019-04-25 at 10:42 -0700, Eric Anholt wrote: >> Paul Kocialkowski writes: >>=20 >> > The binner BO is not required until the V3D is in use, so avoid >> > allocating it at probe and do it on the first non-dumb BO allocation. >> >=20 >> > Keep track of which clients are using the V3D and liberate the buffer >> > when there is none left, using a kref. Protect the logic with a >> > mutex to avoid race conditions. >> >=20 >> > The binner BO is created at the time of the first render ioctl and is >> > destroyed when there is no client and no exec job using it left. >> >=20 >> > The Out-Of-Memory (OOM) interrupt also gets some tweaking, to avoid >> > enabling it before having allocated a binner bo. >> >=20 >> > We also want to keep the BO alive during runtime suspend/resume to avo= id >> > failing to allocate it at resume. This happens when the CMA pool is >> > full at that point and results in a hard crash. >> >=20 >> > Signed-off-by: Paul Kocialkowski >> > --- >> > drivers/gpu/drm/vc4/vc4_bo.c | 33 +++++++++++++++++++- >> > drivers/gpu/drm/vc4/vc4_drv.c | 6 ++++ >> > drivers/gpu/drm/vc4/vc4_drv.h | 14 +++++++++ >> > drivers/gpu/drm/vc4/vc4_gem.c | 13 ++++++++ >> > drivers/gpu/drm/vc4/vc4_irq.c | 21 +++++++++---- >> > drivers/gpu/drm/vc4/vc4_v3d.c | 58 +++++++++++++++++++++++++++-------- >> > 6 files changed, 125 insertions(+), 20 deletions(-) >> >=20 >> > diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo= .c >> > index 88ebd681d7eb..2b3ec5926fe2 100644 >> > --- a/drivers/gpu/drm/vc4/vc4_bo.c >> > +++ b/drivers/gpu/drm/vc4/vc4_bo.c >> > @@ -799,13 +799,38 @@ vc4_prime_import_sg_table(struct drm_device *dev, >> > return obj; >> > } >> >=20=20 >> > +static int vc4_grab_bin_bo(struct vc4_dev *vc4, struct vc4_file *vc4f= ile) >> > +{ >> > + int ret; >> > + >> > + if (!vc4->v3d) >> > + return -ENODEV; >> > + >> > + if (vc4file->bin_bo_used) >> > + return 0; >> > + >> > + ret =3D vc4_v3d_bin_bo_get(vc4); >> > + if (ret) >> > + return ret; >> > + >> > + vc4file->bin_bo_used =3D true; >>=20 >> I think I found one last race. Multiple threads could be in an ioctl >> trying to grab the bin BO at the same time (while this is only during >> app startup, since the fd only needs to get the ref once, it's >> particularly plausible given that allocating the bin BO is slow). I >> think if you replace this line with: >>=20 >> mutex_lock(&vc4->bin_bo_lock); >> if (vc4file->bin_bo_used) { >> mutex_unlock(&vc4->bin_bo_lock); >> vc4_v3d_bin_bo_put(vc4); >> } else { >> vc4file->bin_bo_used =3D true; >> mutex_unlock(&vc4->bin_bo_lock); >> } > > Huh, very good catch once again, thanks! It took me some time to grasp > this one, but as far as I understand, the risk is that we could ref our > bin bo twice (although it would only be allocated once) since > bin_bo_used is not protected. > > I'd like to suggest another solution, which would avoid re-locking and > doing an extra put if we got an extra ref: adding a "bool *used" > argument to vc4_v3d_bin_bo_get and, which only gets dereferenced with > the bin_bo lock held. Then we can skip obtaining a new reference if > (used && *used) in vc4_v3d_bin_bo_get. > > So we could pass a pointer to vc4file->bin_bo_used for vc4_grab_bin_bo > and exec->bin_bo_used for the exec case (where there is no such issue > since we'll only ever try to _get the bin bo once there anyway). > > What do you think? I like it! --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEE/JuuFDWp9/ZkuCBXtdYpNtH8nugFAlzLNpEACgkQtdYpNtH8 nuhALRAApZt7IqOa5t+ZSGZt1v8iX5qpd40P+ssx8Iq7L52Rd3OYItwCk38Mcxla UutDWr0LMMNDr9AkXvFOw4gR3xR2Tjzoi5mggR25hZCVB92xECXpLUc+HkH64mxk VbROrGdV5v4qlnEu1s0AwyUHsDdb+lr5jMS3OqWvYTHYCMX4Bft2HoXENypQD+MQ ZKdJXDnDLlR2uPqPfpIQJbsaHOzRufq4JdgokxEaHaOF3sAUcQbekGPY5ZgZF6uZ IZ0iI7mHMUt245ewIjpZrvWZjB+raqDJdzQQtorxwfc2EGJHhKQILQTJ2zC47AqU Mb7r6jeU6zMh4tupXopo+OpURZJA28fUqkE9+yyqjrPDeh2trJgQbfEEMuK3oREc NXmSwXWuW6zCk0xgr3QrbfCjHbMRSeJcKdSg0i/6+MkGoinWzBjE1KDRFtjgYQVM ykXIDATYVzV0lTBYtSk3/Cgv3Gk0sGJ5J149xVaUqnAuCfbrtVN5BV5TipE3N6GX 9U5MybuD8MkywvkRrnpCsupUGY8tB1QJfZGo+2nuCiFfcCZvTq17bDwrMa1CW/Hc yJZ3gnq91xOsCckqKD683cT58YohdIKPu7QBLSMJi3SAq8k1eHNBmLCry5etPZY+ ux7Kd48np0r/N0ja6oz+mZlLcxoj+gCP3hxnpBQMSHUEBcEfmGw= =qPta -----END PGP SIGNATURE----- --=-=-=--