[PATCH v4 1/1] drm/fb-helper: Avoid race with DRM userspace
Daniel Vetter
daniel at ffwll.ch
Mon May 6 07:54:57 UTC 2019
On Sun, May 05, 2019 at 11:16:54AM +0200, Noralf Trønnes wrote:
>
>
> Den 04.05.2019 14.34, skrev Noralf Trønnes:
> >
> >
> > Den 25.04.2019 10.31, skrev Noralf Trønnes:
> >> drm_fb_helper_is_bound() is used to check if DRM userspace is in control.
> >> This is done by looking at the fb on the primary plane. By the time
> >> fb-helper gets around to committing, it's possible that the facts have
> >> changed.
> >>
> >> Avoid this race by holding the drm_device->master_mutex lock while
> >> committing. When DRM userspace does its first open, it will now wait
> >> until fb-helper is done. The helper will stay away if there's a master.
> >>
> >> Locking rule: Always take the fb-helper lock first.
> >>
> >> v2:
> >> - Remove drm_fb_helper_is_bound() (Daniel Vetter)
> >> - No need to check fb_helper->dev->master in
> >> drm_fb_helper_single_fb_probe(), restore_fbdev_mode() has the check.
> >>
> >> Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> >> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
> >> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> >> ---
> >> drivers/gpu/drm/drm_auth.c | 20 ++++++++
> >> drivers/gpu/drm/drm_fb_helper.c | 90 ++++++++++++++++-----------------
> >> drivers/gpu/drm/drm_internal.h | 2 +
> >> 3 files changed, 67 insertions(+), 45 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
> >> index 1669c42c40ed..db199807b7dc 100644
> >> --- a/drivers/gpu/drm/drm_auth.c
> >> +++ b/drivers/gpu/drm/drm_auth.c
> >> @@ -368,3 +368,23 @@ void drm_master_put(struct drm_master **master)
> >> *master = NULL;
> >> }
> >> EXPORT_SYMBOL(drm_master_put);
> >> +
> >> +/* Used by drm_client and drm_fb_helper */
> >> +bool drm_master_internal_acquire(struct drm_device *dev)
> >> +{
> >> + mutex_lock(&dev->master_mutex);
> >> + if (dev->master) {
> >> + mutex_unlock(&dev->master_mutex);
> >> + return false;
> >> + }
> >> +
> >> + return true;
> >> +}
> >> +EXPORT_SYMBOL(drm_master_internal_acquire);
> >> +
> >> +/* Used by drm_client and drm_fb_helper */
> >> +void drm_master_internal_release(struct drm_device *dev)
> >> +{
> >> + mutex_unlock(&dev->master_mutex);
> >> +}
> >> +EXPORT_SYMBOL(drm_master_internal_release);
> >> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> >> index 2339f0f8f5a8..578428461391 100644
> >> --- a/drivers/gpu/drm/drm_fb_helper.c
> >> +++ b/drivers/gpu/drm/drm_fb_helper.c
> >> @@ -44,6 +44,7 @@
> >>
> >> #include "drm_crtc_internal.h"
> >> #include "drm_crtc_helper_internal.h"
> >> +#include "drm_internal.h"
> >>
> >> static bool drm_fbdev_emulation = true;
> >> module_param_named(fbdev_emulation, drm_fbdev_emulation, bool, 0600);
> >> @@ -509,7 +510,7 @@ static int restore_fbdev_mode_legacy(struct drm_fb_helper *fb_helper)
> >> return ret;
> >> }
> >>
> >> -static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
> >> +static int restore_fbdev_mode_force(struct drm_fb_helper *fb_helper)
> >> {
> >> struct drm_device *dev = fb_helper->dev;
> >>
> >> @@ -519,6 +520,21 @@ static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
> >> return restore_fbdev_mode_legacy(fb_helper);
> >> }
> >>
> >> +static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
> >> +{
> >> + struct drm_device *dev = fb_helper->dev;
> >> + int ret;
> >> +
> >> + if (!drm_master_internal_acquire(dev))
> >> + return -EBUSY;
> >> +
> >> + ret = restore_fbdev_mode_force(fb_helper);
> >> +
> >> + drm_master_internal_release(dev);
> >> +
> >> + return ret;
> >> +}
> >> +
> >> /**
> >> * drm_fb_helper_restore_fbdev_mode_unlocked - restore fbdev configuration
> >> * @fb_helper: driver-allocated fbdev helper, can be NULL
> >
> > The Intel CI doesn't like this patch. AFAICT the reason is that the
> > igt at kms_fbcon_fbt@psr-suspend test expects fbcon to work while it has an
> > open fd that is master. This doesn't match the new rule of bailing out
> > if there's a master.
> >
> > Adding this debug output:
> >
> > @@ -558,6 +558,17 @@ int
> > drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
> > return 0;
> >
> > mutex_lock(&fb_helper->lock);
> > +if (READ_ONCE(fb_helper->dev->master)) {
> > + int level = default_message_loglevel;
> > +
> > + default_message_loglevel = LOGLEVEL_DEBUG;
> > + printk("\n");
> > + printk("\n");
> > + printk("%s\n", __func__);
> > + printk(" THERE IS A MASTER\n");
> > + dump_stack();
> > + default_message_loglevel = level;
> > +}
> > ret = restore_fbdev_mode_force(fb_helper);
> >
> > do_delayed = fb_helper->delayed_hotplug;
> >
> > Gives these log entries:
> >
> > <7> [1857.940072] drm_fb_helper_restore_fbdev_mode_unlocked
> > <7> [1857.940074] THERE IS A MASTER
> > <7> [1857.940079] CPU: 4 PID: 8209 Comm: kms_fbcon_fbt Tainted: G U
> > 5.1.0-rc7-CI-Trybot_4252+ #1
> > <7> [1857.940081] Hardware name: Intel Corporation Ice Lake Client
> > Platform/IceLake U DDR4 SODIMM PD RVP, BIOS
> > ICLSFWR1.R00.3121.A00.1903190527 03/19/2019
> > <7> [1857.940083] Call Trace:
> > <7> [1857.940091] dump_stack+0x67/0x9b
> > <7> [1857.940099] drm_fb_helper_restore_fbdev_mode_unlocked+0xda/0xf0
> > <7> [1857.940104] drm_fb_helper_set_par+0x24/0x50
> > <7> [1857.940188] intel_fbdev_set_par+0x11/0x40 [i915]
> > <7> [1857.940197] fb_set_var+0x17a/0x3f0
> > <7> [1857.940212] ? __lock_acquire+0x49f/0x1590
> > <7> [1857.940230] fbcon_blank+0x192/0x2e0
> > <7> [1857.940235] ? __lock_acquire+0x49f/0x1590
> > <7> [1857.940254] do_unblank_screen+0xa1/0x170
> > <7> [1857.940260] vt_ioctl+0x505/0x11d0
> > <7> [1857.940270] tty_ioctl+0xee/0x940
> > <7> [1857.940274] ? lockdep_hardirqs_off+0x94/0xd0
> > <7> [1857.940278] ? __slab_free+0x24e/0x4f0
> > <7> [1857.940287] ? _raw_spin_unlock_irqrestore+0x39/0x60
> > <7> [1857.940291] ? kmem_cache_free+0x279/0x2e0
> > <7> [1857.940299] do_vfs_ioctl+0xa0/0x6e0
> > <7> [1857.940305] ? do_sys_open+0x13b/0x250
> > <7> [1857.940311] ? rcu_read_lock_sched_held+0x6f/0x80
> > <7> [1857.940313] ? kmem_cache_free+0x283/0x2e0
> > <7> [1857.940321] ksys_ioctl+0x35/0x60
> > <7> [1857.940328] __x64_sys_ioctl+0x11/0x20
> > <7> [1857.940332] do_syscall_64+0x55/0x190
> > <7> [1857.940337] entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > <7> [1857.940341] RIP: 0033:0x7faf8f0825d7
> > <7> [1857.940345] Code: b3 66 90 48 8b 05 b1 48 2d 00 64 c7 00 26 00 00
> > 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00
> > 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 81 48 2d 00 f7 d8 64 89 01 48
> > <7> [1857.940347] RSP: 002b:00007ffddf6a94b8 EFLAGS: 00000246 ORIG_RAX:
> > 0000000000000010
> > <7> [1857.940351] RAX: ffffffffffffffda RBX: 0000000000000000 RCX:
> > 00007faf8f0825d7
> > <7> [1857.940353] RDX: 0000000000000000 RSI: 0000000000004b3a RDI:
> > 000000000000000a
> > <7> [1857.940355] RBP: 0000000000000000 R08: 0000000000000000 R09:
> > 00000000000000ab
> > <7> [1857.940357] R10: 0000000000000000 R11: 0000000000000246 R12:
> > 0000000000004b3a
> > <7> [1857.940359] R13: 000000000000000a R14: 0000000000000000 R15:
> > 0000000000000000
> > <6> [1861.481078] [IGT] kms_fbcon_fbt: exiting, ret=99
> >
> > Patches:
> > https://patchwork.freedesktop.org/series/59951/#rev8
> > Failing test:
> > https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_4252/shard-iclb7/igt@kms_fbcon_fbt@psr-suspend.html
> >
>
> Actually there's two failing tests, this one as well:
>
> * igt at kms_fbcon_fbt at psr:
> - shard-skl: NOTRUN -> [FAIL][1]
> [1]:
> https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_4252/shard-skl7/igt@kms_fbcon_fbt@psr.html
I think the test should change. Our igt fbcon/fbdev tests started as some
quick hacks and evolved from there ...
-Daniel
>
>
> >
> > If I make this change and don't check for master, then it's fine:
> >
> > @@ -542,7 +558,7 @@ int
> > drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
> > return 0;
> >
> > mutex_lock(&fb_helper->lock);
> > - ret = restore_fbdev_mode(fb_helper);
> > + ret = restore_fbdev_mode_force(fb_helper);
> >
> > do_delayed = fb_helper->delayed_hotplug;
> > if (do_delayed)
> >
> > https://patchwork.freedesktop.org/series/59951/#rev9
> >
> > Should I make this change, or should the test change?
> >
> > Noralf.
> >
> >> @@ -556,34 +572,6 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
> >> }
> >> EXPORT_SYMBOL(drm_fb_helper_restore_fbdev_mode_unlocked);
> >>
> >> -static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper)
> >> -{
> >> - struct drm_device *dev = fb_helper->dev;
> >> - struct drm_crtc *crtc;
> >> - int bound = 0, crtcs_bound = 0;
> >> -
> >> - /*
> >> - * Sometimes user space wants everything disabled, so don't steal the
> >> - * display if there's a master.
> >> - */
> >> - if (READ_ONCE(dev->master))
> >> - return false;
> >> -
> >> - drm_for_each_crtc(crtc, dev) {
> >> - drm_modeset_lock(&crtc->mutex, NULL);
> >> - if (crtc->primary->fb)
> >> - crtcs_bound++;
> >> - if (crtc->primary->fb == fb_helper->fb)
> >> - bound++;
> >> - drm_modeset_unlock(&crtc->mutex);
> >> - }
> >> -
> >> - if (bound < crtcs_bound)
> >> - return false;
> >> -
> >> - return true;
> >> -}
> >> -
> >> #ifdef CONFIG_MAGIC_SYSRQ
> >> /*
> >> * restore fbcon display for all kms driver's using this helper, used for sysrq
> >> @@ -604,7 +592,7 @@ static bool drm_fb_helper_force_kernel_mode(void)
> >> continue;
> >>
> >> mutex_lock(&helper->lock);
> >> - ret = restore_fbdev_mode(helper);
> >> + ret = restore_fbdev_mode_force(helper);
> >> if (ret)
> >> error = true;
> >> mutex_unlock(&helper->lock);
> >> @@ -663,20 +651,22 @@ static void dpms_legacy(struct drm_fb_helper *fb_helper, int dpms_mode)
> >> static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
> >> {
> >> struct drm_fb_helper *fb_helper = info->par;
> >> + struct drm_device *dev = fb_helper->dev;
> >>
> >> /*
> >> * For each CRTC in this fb, turn the connectors on/off.
> >> */
> >> mutex_lock(&fb_helper->lock);
> >> - if (!drm_fb_helper_is_bound(fb_helper)) {
> >> - mutex_unlock(&fb_helper->lock);
> >> - return;
> >> - }
> >> + if (!drm_master_internal_acquire(dev))
> >> + goto unlock;
> >>
> >> - if (drm_drv_uses_atomic_modeset(fb_helper->dev))
> >> + if (drm_drv_uses_atomic_modeset(dev))
> >> restore_fbdev_mode_atomic(fb_helper, dpms_mode == DRM_MODE_DPMS_ON);
> >> else
> >> dpms_legacy(fb_helper, dpms_mode);
> >> +
> >> + drm_master_internal_release(dev);
> >> +unlock:
> >> mutex_unlock(&fb_helper->lock);
> >> }
> >>
> >> @@ -1509,6 +1499,7 @@ static int setcmap_atomic(struct fb_cmap *cmap, struct fb_info *info)
> >> int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> >> {
> >> struct drm_fb_helper *fb_helper = info->par;
> >> + struct drm_device *dev = fb_helper->dev;
> >> int ret;
> >>
> >> if (oops_in_progress)
> >> @@ -1516,9 +1507,9 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> >>
> >> mutex_lock(&fb_helper->lock);
> >>
> >> - if (!drm_fb_helper_is_bound(fb_helper)) {
> >> + if (!drm_master_internal_acquire(dev)) {
> >> ret = -EBUSY;
> >> - goto out;
> >> + goto unlock;
> >> }
> >>
> >> if (info->fix.visual == FB_VISUAL_TRUECOLOR)
> >> @@ -1528,7 +1519,8 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> >> else
> >> ret = setcmap_legacy(cmap, info);
> >>
> >> -out:
> >> + drm_master_internal_release(dev);
> >> +unlock:
> >> mutex_unlock(&fb_helper->lock);
> >>
> >> return ret;
> >> @@ -1548,12 +1540,13 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
> >> unsigned long arg)
> >> {
> >> struct drm_fb_helper *fb_helper = info->par;
> >> + struct drm_device *dev = fb_helper->dev;
> >> struct drm_mode_set *mode_set;
> >> struct drm_crtc *crtc;
> >> int ret = 0;
> >>
> >> mutex_lock(&fb_helper->lock);
> >> - if (!drm_fb_helper_is_bound(fb_helper)) {
> >> + if (!drm_master_internal_acquire(dev)) {
> >> ret = -EBUSY;
> >> goto unlock;
> >> }
> >> @@ -1591,11 +1584,12 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
> >> }
> >>
> >> ret = 0;
> >> - goto unlock;
> >> + break;
> >> default:
> >> ret = -ENOTTY;
> >> }
> >>
> >> + drm_master_internal_release(dev);
> >> unlock:
> >> mutex_unlock(&fb_helper->lock);
> >> return ret;
> >> @@ -1847,15 +1841,18 @@ int drm_fb_helper_pan_display(struct fb_var_screeninfo *var,
> >> return -EBUSY;
> >>
> >> mutex_lock(&fb_helper->lock);
> >> - if (!drm_fb_helper_is_bound(fb_helper)) {
> >> - mutex_unlock(&fb_helper->lock);
> >> - return -EBUSY;
> >> + if (!drm_master_internal_acquire(dev)) {
> >> + ret = -EBUSY;
> >> + goto unlock;
> >> }
> >>
> >> if (drm_drv_uses_atomic_modeset(dev))
> >> ret = pan_display_atomic(var, info);
> >> else
> >> ret = pan_display_legacy(var, info);
> >> +
> >> + drm_master_internal_release(dev);
> >> +unlock:
> >> mutex_unlock(&fb_helper->lock);
> >>
> >> return ret;
> >> @@ -2014,7 +2011,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
> >> DRM_INFO("Cannot find any crtc or sizes\n");
> >>
> >> /* First time: disable all crtc's.. */
> >> - if (!fb_helper->deferred_setup && !READ_ONCE(fb_helper->dev->master))
> >> + if (!fb_helper->deferred_setup)
> >> restore_fbdev_mode(fb_helper);
> >> return -EAGAIN;
> >> }
> >> @@ -3028,6 +3025,7 @@ EXPORT_SYMBOL(drm_fb_helper_initial_config);
> >> */
> >> int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
> >> {
> >> + struct drm_device *dev = fb_helper->dev;
> >> int err = 0;
> >>
> >> if (!drm_fbdev_emulation || !fb_helper)
> >> @@ -3040,12 +3038,14 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
> >> return err;
> >> }
> >>
> >> - if (!fb_helper->fb || !drm_fb_helper_is_bound(fb_helper)) {
> >> + if (!fb_helper->fb || !drm_master_internal_acquire(dev)) {
> >> fb_helper->delayed_hotplug = true;
> >> mutex_unlock(&fb_helper->lock);
> >> return err;
> >> }
> >>
> >> + drm_master_internal_release(dev);
> >> +
> >> DRM_DEBUG_KMS("\n");
> >>
> >> drm_setup_crtcs(fb_helper, fb_helper->fb->width, fb_helper->fb->height);
> >> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> >> index d9a483a5fce0..3ee97c9998a2 100644
> >> --- a/drivers/gpu/drm/drm_internal.h
> >> +++ b/drivers/gpu/drm/drm_internal.h
> >> @@ -91,6 +91,8 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
> >> struct drm_file *file_priv);
> >> int drm_master_open(struct drm_file *file_priv);
> >> void drm_master_release(struct drm_file *file_priv);
> >> +bool drm_master_internal_acquire(struct drm_device *dev);
> >> +void drm_master_internal_release(struct drm_device *dev);
> >>
> >> /* drm_sysfs.c */
> >> extern struct class *drm_class;
> >>
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
More information about the dri-devel
mailing list