Hi Daniel,
Please see below, I've had several bisection results pointing at that commit over the week-end on mainline but also on linux-next and net-next. While the peach-pi is a bit flaky at the moment and is likely to have more than one issue, it does seem like this commit is causing some well reproducible kernel hang.
Here's a re-run with v4.15-rc3 showing the issue:
https://lava.collabora.co.uk/scheduler/job/1018478
and here's another one with the change mentioned below reverted:
https://lava.collabora.co.uk/scheduler/job/1018479
They both show a warning about "unbalanced disables for lcd_vdd", I don't know if this is related as I haven't investigated any further. It does appear to reliably hang with v4.15-rc3 and boot most of the time with the commit reverted though.
The automated kernelci.org bisection is still an experimental tool and it may well be a false positive, so please take this result with a pinch of salt...
Hope this helps!
Best wishes, Guillaume
-------- Forwarded Message -------- Subject: mainline/master boot bisection: v4.15-rc3 on peach-pi #3228-staging Date: Mon, 11 Dec 2017 08:25:55 +0000 (UTC) From: kernelci.org bot bot@kernelci.org To: guillaume.tucker@collabora.com
Bisection result for mainline/master (v4.15-rc3) on peach-pi
Good known revision:
c6b3e96 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
Bad known revision:
50c4c4e Linux 4.15-rc3
Extra parameters:
Tree: mainline Branch: master Target: peach-pi Lab: lab-collabora Defconfig: exynos_defconfig Plan: boot
Breaking commit found:
------------------------------------------------------------------------------- commit a703c55004e1c5076d57e43771b3e11117796ea0 Author: Daniel Vetter daniel.vetter@ffwll.ch Date: Mon Dec 4 21:48:18 2017 +0100
drm: safely free connectors from connector_iter
In
commit 613051dac40da1751ab269572766d3348d45a197 Author: Daniel Vetter daniel.vetter@ffwll.ch Date: Wed Dec 14 00:08:06 2016 +0100
drm: locking&new iterators for connector_list
we've went to extreme lengths to make sure connector iterations works in any context, without introducing any additional locking context. This worked, except for a small fumble in the implementation:
When we actually race with a concurrent connector unplug event, and our temporary connector reference turns out to be the final one, then everything breaks: We call the connector release function from whatever context we happen to be in, which can be an irq/atomic context. And connector freeing grabs all kinds of locks and stuff.
Fix this by creating a specially safe put function for connetor_iter, which (in this rare case) punts the cleanup to a worker.
Reported-by: Ben Widawsky ben@bwidawsk.net Cc: Ben Widawsky ben@bwidawsk.net Fixes: 613051dac40d ("drm: locking&new iterators for connector_list") Cc: Dave Airlie airlied@gmail.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sean Paul seanpaul@chromium.org Cc: stable@vger.kernel.org # v4.11+ Reviewed-by: Dave Airlie airlied@gmail.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20171204204818.24745-1-daniel....
diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index 25f4b2e..4820141 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -152,6 +152,16 @@ static void drm_connector_free(struct kref *kref) connector->funcs->destroy(connector); }
+static void drm_connector_free_work_fn(struct work_struct *work) +{ + struct drm_connector *connector = + container_of(work, struct drm_connector, free_work); + struct drm_device *dev = connector->dev; + + drm_mode_object_unregister(dev, &connector->base); + connector->funcs->destroy(connector); +} + /** * drm_connector_init - Init a preallocated connector * @dev: DRM device @@ -181,6 +191,8 @@ int drm_connector_init(struct drm_device *dev, if (ret) return ret;
+ INIT_WORK(&connector->free_work, drm_connector_free_work_fn); + connector->base.properties = &connector->properties; connector->dev = dev; connector->funcs = funcs; @@ -529,6 +541,18 @@ void drm_connector_list_iter_begin(struct drm_device *dev, } EXPORT_SYMBOL(drm_connector_list_iter_begin);
+/* + * Extra-safe connector put function that works in any context. Should only be + * used from the connector_iter functions, where we never really expect to + * actually release the connector when dropping our final reference. + */ +static void +drm_connector_put_safe(struct drm_connector *conn) +{ + if (refcount_dec_and_test(&conn->base.refcount.refcount)) + schedule_work(&conn->free_work); +} + /** * drm_connector_list_iter_next - return next connector * @iter: connectr_list iterator @@ -561,7 +585,7 @@ drm_connector_list_iter_next(struct drm_connector_list_iter *iter) spin_unlock_irqrestore(&config->connector_list_lock, flags);
if (old_conn) - drm_connector_put(old_conn); + drm_connector_put_safe(old_conn);
return iter->conn; } @@ -580,7 +604,7 @@ void drm_connector_list_iter_end(struct drm_connector_list_iter *iter) { iter->dev = NULL; if (iter->conn) - drm_connector_put(iter->conn); + drm_connector_put_safe(iter->conn); lock_release(&connector_list_iter_dep_map, 0, _RET_IP_); } EXPORT_SYMBOL(drm_connector_list_iter_end); diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c index cda8bfa..cc78b3d 100644 --- a/drivers/gpu/drm/drm_mode_config.c +++ b/drivers/gpu/drm/drm_mode_config.c @@ -431,6 +431,8 @@ void drm_mode_config_cleanup(struct drm_device *dev) drm_connector_put(connector); } drm_connector_list_iter_end(&conn_iter); + /* connector_iter drops references in a work item. */ + flush_scheduled_work(); if (WARN_ON(!list_empty(&dev->mode_config.connector_list))) { drm_connector_list_iter_begin(dev, &conn_iter); drm_for_each_connector_iter(connector, &conn_iter) diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h index df9807a..a4649c5 100644 --- a/include/drm/drm_connector.h +++ b/include/drm/drm_connector.h @@ -916,6 +916,14 @@ struct drm_connector { uint8_t num_h_tile, num_v_tile; uint8_t tile_h_loc, tile_v_loc; uint16_t tile_h_size, tile_v_size; + + /** + * @free_work: + * + * Work used only by &drm_connector_iter to be able to clean up a + * connector from any context. + */ + struct work_struct free_work; };
#define obj_to_connector(x) container_of(x, struct drm_connector, base) -------------------------------------------------------------------------------
Git bisection log:
------------------------------------------------------------------------------- git bisect start # good: [c6b3e9693f8a32ba3b07e2f2723886ea2aff4e94] Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux git bisect good c6b3e9693f8a32ba3b07e2f2723886ea2aff4e94 # bad: [50c4c4e268a2d7a3e58ebb698ac74da0de40ae36] Linux 4.15-rc3 git bisect bad 50c4c4e268a2d7a3e58ebb698ac74da0de40ae36 # bad: [e9ef1fe312b533592e39cddc1327463c30b0ed8d] Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net git bisect bad e9ef1fe312b533592e39cddc1327463c30b0ed8d # bad: [77071bc6c472bb0b36818f3e9595114cdf98c86d] Merge tag 'media/v4.15-2' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media git bisect bad 77071bc6c472bb0b36818f3e9595114cdf98c86d # bad: [4066aa72f9f2886105c6f747d7f9bd4f14f53c12] Merge tag 'drm-fixes-for-v4.15-rc3' of git://people.freedesktop.org/~airlied/linux git bisect bad 4066aa72f9f2886105c6f747d7f9bd4f14f53c12 # bad: [96980844bb4b74d2e7ce93d907670658e39a3992] Merge tag 'drm-intel-fixes-2017-12-07' of git://anongit.freedesktop.org/drm/drm-intel into drm-fixes git bisect bad 96980844bb4b74d2e7ce93d907670658e39a3992 # bad: [120a264f9c2782682027d931d83dcbd22e01da80] drm/exynos: gem: Drop NONCONTIG flag for buffers allocated without IOMMU git bisect bad 120a264f9c2782682027d931d83dcbd22e01da80 # good: [2bf257d662509553ae226239e7dc1c3d00636ca6] drm/ttm: roundup the shrink request to prevent skip huge pool git bisect good 2bf257d662509553ae226239e7dc1c3d00636ca6 # good: [db8f884ca7fe6af64d443d1510464efe23826131] Merge branch 'drm-fixes-4.15' of git://people.freedesktop.org/~agd5f/linux into drm-fixes git bisect good db8f884ca7fe6af64d443d1510464efe23826131 # bad: [bd3a3a2e92624942a143e485c83e641b2492d828] Merge tag 'drm-misc-fixes-2017-12-06' of git://anongit.freedesktop.org/drm/drm-misc into drm-fixes git bisect bad bd3a3a2e92624942a143e485c83e641b2492d828 # bad: [a703c55004e1c5076d57e43771b3e11117796ea0] drm: safely free connectors from connector_iter git bisect bad a703c55004e1c5076d57e43771b3e11117796ea0 # first bad commit: [a703c55004e1c5076d57e43771b3e11117796ea0] drm: safely free connectors from connector_iter -------------------------------------------------------------------------------