Patch "drm/atomic: Make drm_atomic_legacy_backoff reset crtc->acquire_ctx" has been added to the 4.6-stable tree

This is a note to let you know that I've just added the patch titled

    drm/atomic: Make drm_atomic_legacy_backoff reset crtc->acquire_ctx

to the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-atomic-make-drm_atomic_legacy_backoff-reset-crtc-acquire_ctx.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Maarten Lankhorst <[email protected]>
Date: Thu, 23 Jun 2016 13:45:06 +0200
Subject: drm/atomic: Make drm_atomic_legacy_backoff reset crtc->acquire_ctx

From: Maarten Lankhorst <[email protected]>

commit 81e257e964268d050f8e9188becd44d50f241d72 upstream.

Atomic updates may acquire more state than initially locked through drm_modeset_lock_crtc, running with heavy stress can cause a WARN_ON(crtc->acquire_ctx) in drm_modeset_lock_crtc:

[  601.491296] ------------[ cut here ]------------
[  601.491366] WARNING: CPU: 0 PID: 2411 at
drivers/gpu/drm/drm_modeset_lock.c:191 drm_modeset_lock_crtc+0xeb/0xf0 [drm]
[  601.491369] Modules linked in: drm i915 drm_kms_helper
[  601.491414] CPU: 0 PID: 2411 Comm: kms_cursor_lega Tainted: G     U 4.7.0-rc4-patser+ #4798
[  601.491417] Hardware name: Intel Corporation Skylake Client
[  601.491420]  0000000000000000 ffff88044d153c98 ffffffff812ead28 0000000000000000
[  601.491425]  0000000000000000 ffff88044d153cd8 ffffffff810868e6 000000bf58058030
[  601.491431]  ffff880088b415e8 ffff880458058030 ffff88008a271548 ffff88008a271568
[  601.491436] Call Trace:
[  601.491443]  [<ffffffff812ead28>] dump_stack+0x4d/0x65
[  601.491447]  [<ffffffff810868e6>] __warn+0xc6/0xe0
[  601.491452]  [<ffffffff81086968>] warn_slowpath_null+0x18/0x20
[  601.491472]  [<ffffffffc00d4ffb>] drm_modeset_lock_crtc+0xeb/0xf0 [drm]
[  601.491491]  [<ffffffffc00c5526>] drm_mode_cursor_common+0x66/0x180 [drm]
[  601.491509]  [<ffffffffc00c91cc>] drm_mode_cursor_ioctl+0x3c/0x40 [drm]
[  601.491524]  [<ffffffffc00bc94d>] drm_ioctl+0x14d/0x530 [drm]
[  601.491540]  [<ffffffffc00c9190>] ? drm_mode_setcrtc+0x520/0x520 [drm]
[  601.491545]  [<ffffffff81176aeb>] ? handle_mm_fault+0x106b/0x1430
[  601.491550]  [<ffffffff81108441>] ? stop_one_cpu+0x61/0x70
[  601.491556]  [<ffffffff811bb71d>] do_vfs_ioctl+0x8d/0x570
[  601.491560]  [<ffffffff81290d7e>] ? security_file_ioctl+0x3e/0x60
[  601.491565]  [<ffffffff811bbc74>] SyS_ioctl+0x74/0x80
[  601.491571]  [<ffffffff810e321c>] ? posix_get_monotonic_raw+0xc/0x10
[  601.491576]  [<ffffffff8175b11b>] entry_SYSCALL_64_fastpath+0x13/0x8f
[  601.491581] ---[ end trace 56f3d3d85f000d00 ]---

For good measure, test mode_config.acquire_ctx too, although this should never happen.

Testcase: kms_cursor_legacy

---
 drivers/gpu/drm/drm_atomic.c |   27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

@@ -1288,14 +1288,39 @@ EXPORT_SYMBOL(drm_atomic_add_affected_pl
  */
 void drm_atomic_legacy_backoff(struct drm_atomic_state *state)
 {
+	struct drm_device *dev = state->dev;
+	unsigned crtc_mask = 0;
+	struct drm_crtc *crtc;
 	int ret;
+	bool global = false;
+
+	drm_for_each_crtc(crtc, dev) {
+		if (crtc->acquire_ctx != state->acquire_ctx)
+			continue;
+
+		crtc_mask |= drm_crtc_mask(crtc);
+		crtc->acquire_ctx = NULL;
+	}
+
+	if (WARN_ON(dev->mode_config.acquire_ctx == state->acquire_ctx)) {
+		global = true;
+
+		dev->mode_config.acquire_ctx = NULL;
+	}
 
 retry:
 	drm_modeset_backoff(state->acquire_ctx);
 
-	ret = drm_modeset_lock_all_ctx(state->dev, state->acquire_ctx);
+	ret = drm_modeset_lock_all_ctx(dev, state->acquire_ctx);
 	if (ret)
 		goto retry;
+
+	drm_for_each_crtc(crtc, dev)
+		if (drm_crtc_mask(crtc) & crtc_mask)
+			crtc->acquire_ctx = state->acquire_ctx;
+
+	if (global)
+		dev->mode_config.acquire_ctx = state->acquire_ctx;
 }
 EXPORT_SYMBOL(drm_atomic_legacy_backoff);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.6/drm-atomic-make-drm_atomic_legacy_backoff-reset-crtc-acquire_ctx.patch queue-4.6/locking-ww_mutex-report-recursive-ww_mutex-locking-early.patch