From: Peter Wu <peter@lekensteyn.nl>
To: "Noralf Trønnes" <noralf@tronnes.org>
Cc: lkp@01.org, rong.a.chen@intel.com,
Daniel Vetter <daniel.vetter@ffwll.ch>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
dri-devel@lists.freedesktop.org, kraxel@redhat.com,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] drm/fb-helper: fix leaks in error path of drm_fb_helper_fbdev_setup
Date: Mon, 24 Dec 2018 00:10:33 +0100 [thread overview]
Message-ID: <20181223231033.GA31596@al> (raw)
In-Reply-To: <ad4be2e7-b53c-97b5-7029-83f4017e4643@tronnes.org>
On Sun, Dec 23, 2018 at 02:55:52PM +0100, Noralf Trønnes wrote:
>
>
> Den 23.12.2018 01.55, skrev Peter Wu:
> > After drm_fb_helper_fbdev_setup calls drm_fb_helper_init,
> > "dev->fb_helper" will be initialized (and thus drm_fb_helper_fini will
> > have some effect). After that, drm_fb_helper_initial_config is called
> > which may call the "fb_probe" driver callback.
> >
> > This driver callback may call drm_fb_helper_defio_init (as is done by
> > drm_fb_helper_generic_probe) or set a framebuffer (as is done by bochs)
> > as documented. These are normally cleaned up on exit by
> > drm_fb_helper_fbdev_teardown which also calls drm_fb_helper_fini.
> >
> > If an error occurs after "fb_probe", but before setup is complete, then
> > calling just drm_fb_helper_fini will leak resources. This was triggered
> > by df2052cc922 ("bochs: convert to drm_fb_helper_fbdev_setup/teardown"):
> >
> > [ 50.008030] bochsdrmfb: enable CONFIG_FB_LITTLE_ENDIAN to support this framebuffer
> > [ 50.009436] bochs-drm 0000:00:02.0: [drm:drm_fb_helper_fbdev_setup] *ERROR* fbdev: Failed to set configuration (ret=-38)
> > [ 50.011456] [drm] Initialized bochs-drm 1.0.0 20130925 for 0000:00:02.0 on minor 2
> > [ 50.013604] WARNING: CPU: 1 PID: 1 at drivers/gpu/drm/drm_mode_config.c:477 drm_mode_config_cleanup+0x280/0x2a0
> > [ 50.016175] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G T 4.20.0-rc7 #1
> > [ 50.017732] EIP: drm_mode_config_cleanup+0x280/0x2a0
> > ...
> > [ 50.023155] Call Trace:
> > [ 50.023155] ? bochs_kms_fini+0x1e/0x30
> > [ 50.023155] ? bochs_unload+0x18/0x40
> >
> > This can be reproduced with QEMU and CONFIG_FB_LITTLE_ENDIAN=n.
> >
> > Link: https://lkml.kernel.org/r/20181221083226.GI23332@shao2-debian
> > Link: https://lkml.kernel.org/r/20181223004315.GA11455@al
> > Fixes: 8741216396b2 ("drm/fb-helper: Add drm_fb_helper_fbdev_setup/teardown()")
> > Reported-by: kernel test robot <rong.a.chen@intel.com>
> > Cc: Noralf Trønnes <noralf@tronnes.org>
> > Signed-off-by: Peter Wu <peter@lekensteyn.nl>
> > ---
> > drivers/gpu/drm/drm_fb_helper.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > index 9d64f874f965..432e0f3b9267 100644
> > --- a/drivers/gpu/drm/drm_fb_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > @@ -2860,7 +2860,7 @@ int drm_fb_helper_fbdev_setup(struct drm_device *dev,
> > return 0;
> > err_drm_fb_helper_fini:
> > - drm_fb_helper_fini(fb_helper);
> > + drm_fb_helper_fbdev_teardown(dev);
>
> This change will break the error path for drm_fbdev_generic_setup()
> because drm_fb_helper_generic_probe() cleans up on error but doesn't
> clear drm_fb_helper->fb resulting in a double drm_framebuffer_remove().
This should probably considered a bug of drm_fb_helper_generic_probe.
Ownership of fb_helper should remain with the caller. The caller can
detect an error and act accordingly.
> My assumption has been that the drm_fb_helper_funcs->fb_probe callback
> cleans up its resources on error. Clearly this is not the case for bochs, so
> my take on this is that bochsfb_create() needs to clean up on error.
That assumption still holds for bochs. The problem is this sequence:
- drm_fb_helper_fbdev_setup is called.
- fb_probe succeeds (this is crucial).
- register_framebuffer fails.
- error path of setup is triggered.
As fb_helper is fully setup by drivers, the drm_fb_helper core should
fully deallocate it again on the error path or else a leak occurs.
> Gerd has a patchset that switches bochs over to the generic fbdev
> emulation, but ofc that doesn't help with 4.20:
> https://patchwork.freedesktop.org/series/54269/
And that does not help with other users of the drm_fb_helper who use
functions like drm_fb_helper_defio_init. They will likely run in the
same problem.
I don't have a way to test tinydrm or other drivers, but if you force
register_framebuffer to fail, you should be able to reproduce the
problem with drm_fb_helper_generic_probe.
--
Kind regards,
Peter Wu
https://lekensteyn.nl
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2018-12-23 23:10 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20181221083226.GI23332@shao2-debian>
[not found] ` <CAHk-=whM09ZxdrrN-o3k1JOAn0keF5aXtPAcEYiukn7kW7yp2g@mail.gmail.com>
2018-12-23 0:43 ` [LKP] [bochs] df2052cc92: WARNING:at_drivers/gpu/drm/drm_mode_config.c:#drm_mode_config_cleanup Peter Wu
2018-12-23 0:55 ` [PATCH] drm/fb-helper: fix leaks in error path of drm_fb_helper_fbdev_setup Peter Wu
2018-12-23 13:55 ` Noralf Trønnes
2018-12-23 23:10 ` Peter Wu [this message]
2018-12-24 14:52 ` Noralf Trønnes
2018-12-24 15:03 ` Peter Wu
2019-01-05 18:25 ` Noralf Trønnes
2019-01-08 17:55 ` Noralf Trønnes
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181223231033.GA31596@al \
--to=peter@lekensteyn.nl \
--cc=daniel.vetter@ffwll.ch \
--cc=dri-devel@lists.freedesktop.org \
--cc=kraxel@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=lkp@01.org \
--cc=noralf@tronnes.org \
--cc=rong.a.chen@intel.com \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).