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    SubjectRe: [PATCH 4.2 41/54] drm/nouveau/fbcon: take runpm reference when userspace has an open fd
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    On Fri, 2015-10-23 at 10:45 -0700, Greg Kroah-Hartman wrote:
    > 4.2-stable review patch.  If anyone has any objections, please let me know.
    >
    > ------------------
    >
    > From: Ben Skeggs <bskeggs@redhat.com>
    >
    > commit f231976c2e8964ceaa9250e57d27c35ff03825c2 upstream.
    >
    > We need to do this in order to prevent accesses to the device while it's
    > powered down.  Userspace may have an mmap of the fb, and there's no good
    > way (that I know of) to prevent it from touching the device otherwise.
    >
    > This fixes some nasty races between runpm and plymouth on some systems,
    > which result in the GPU getting very upset and hanging the boot.
    >
    > Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    >
    > ---
    >  drivers/gpu/drm/nouveau/nouveau_fbcon.c |   24 ++++++++++++++++++++++++
    >  1 file changed, 24 insertions(+)
    >
    > --- a/drivers/gpu/drm/nouveau/nouveau_fbcon.c
    > +++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
    > @@ -178,8 +178,30 @@ nouveau_fbcon_sync(struct fb_info *info)
    >  > > return 0;
    >  }
    >  
    > +static int
    > +nouveau_fbcon_open(struct fb_info *info, int user)
    > +{
    > +> > struct nouveau_fbdev *fbcon = info->par;
    > +> > struct nouveau_drm *drm = nouveau_drm(fbcon->dev);
    > +> > int ret = pm_runtime_get_sync(drm->dev->dev);
    > + if (ret < 0 && ret != -EACCES)
    > + return ret;
    > +> > return 0;
    > +}
    [...]

    As pm_runtime_get_sync() always bumps the usage count, the error path
    here should call pm_runtime_put().

    Ben.
    >
    --
    Ben Hutchings
    Beware of bugs in the above code;
    I have only proved it correct, not tried it. - Donald Knuth[unhandled content-type:application/pgp-signature]
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