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| /openbmc/linux/drivers/gpu/drm/i915/ |
| H A D | i915_irq.c | diff 17e1df07df0fbc77696a1e1b6ccf9f2e5af70e40 Sun Sep 08 14:57:13 CDT 2013 Daniel Vetter <daniel.vetter@ffwll.ch> drm/i915: fix wait_for_pending_flips vs gpu hang deadlock
My g33 here seems to be shockingly good at hitting them all. This time
around kms_flip/flip-vs-panning-vs-hang blows up:
intel_crtc_wait_for_pending_flips correctly checks for gpu hangs and
if a gpu hang is pending aborts the wait for outstanding flips so that
the setcrtc call will succeed and release the crtc mutex. And the gpu
hang handler needs that lock in intel_display_handle_reset to be able
to complete outstanding flips.
The problem is that we can race in two ways:
- Waiters on the dev_priv->pending_flip_queue aren't woken up after
we've the reset as pending, but before we actually start the reset
work. This means that the waiter doesn't notice the pending reset
and hence will keep on hogging the locks.
Like with dev->struct_mutex and the ring->irq_queue wait queues we
there need to wake up everyone that potentially holds a lock which
the reset handler needs.
- intel_display_handle_reset was called _after_ we've already
signalled the completion of the reset work. Which means a waiter
could sneak in, grab the lock and never release it (since the
pageflips won't ever get released).
Similar to resetting the gem state all the reset work must complete
before we update the reset counter. Contrary to the gem reset we
don't need to have a second explicit wake up call since that will
have happened already when completing the pageflips. We also don't
have any issues that the completion happens while the reset state is
still pending - wait_for_pending_flips is only there to ensure we
display the right frame. After a gpu hang&reset events such
guarantees are out the window anyway. This is in contrast to the gem
code where too-early wake-up would result in unnecessary restarting
of ioctls.
Also, since we've gotten these various deadlocks and ordering
constraints wrong so often throw copious amounts of comments at the
code.
This deadlock regression has been introduced in the commit which added
the pageflip reset logic to the gpu hang work:
commit 96a02917a0131e52efefde49c2784c0421d6c439
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date: Mon Feb 18 19:08:49 2013 +0200
drm/i915: Finish page flips and update primary planes after a GPU reset
v2:
- Add comments to explain how the wake_up serves as memory barriers
for the atomic_t reset counter.
- Improve the comments a bit as suggested by Chris Wilson.
- Extract the wake_up calls before/after the reset into a little
i915_error_wake_up and unconditionally wake up the
pending_flip_queue waiters, again as suggested by Chris Wilson.
v3: Throw copious amounts of comments at i915_error_wake_up as
suggested by Chris Wilson.
Cc: stable@vger.kernel.org
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff 122f46badaafbe651f05c2c0f24cadee692f761b Wed Sep 04 10:36:14 CDT 2013 Daniel Vetter <daniel.vetter@ffwll.ch> drm/i915: fix gpu hang vs. flip stall deadlocks
Since we've started to clean up pending flips when the gpu hangs in
commit 96a02917a0131e52efefde49c2784c0421d6c439
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date: Mon Feb 18 19:08:49 2013 +0200
drm/i915: Finish page flips and update primary planes after a GPU reset
the gpu reset work now also grabs modeset locks. But since work items
on our private work queue are not allowed to do that due to the
flush_workqueue from the pageflip code this results in a neat
deadlock:
INFO: task kms_flip:14676 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kms_flip D ffff88019283a5c0 0 14676 13344 0x00000004
ffff88018e62dbf8 0000000000000046 ffff88013bdb12e0 ffff88018e62dfd8
ffff88018e62dfd8 00000000001d3b00 ffff88019283a5c0 ffff88018ec21000
ffff88018f693f00 ffff88018eece000 ffff88018e62dd60 ffff88018eece898
Call Trace:
[<ffffffff8138ee7b>] schedule+0x60/0x62
[<ffffffffa046c0dd>] intel_crtc_wait_for_pending_flips+0xb2/0x114 [i915]
[<ffffffff81050ff4>] ? finish_wait+0x60/0x60
[<ffffffffa0478041>] intel_crtc_set_config+0x7f3/0x81e [i915]
[<ffffffffa031780a>] drm_mode_set_config_internal+0x4f/0xc6 [drm]
[<ffffffffa0319cf3>] drm_mode_setcrtc+0x44d/0x4f9 [drm]
[<ffffffff810e44da>] ? might_fault+0x38/0x86
[<ffffffffa030d51f>] drm_ioctl+0x2f9/0x447 [drm]
[<ffffffff8107a722>] ? trace_hardirqs_off+0xd/0xf
[<ffffffffa03198a6>] ? drm_mode_setplane+0x343/0x343 [drm]
[<ffffffff8112222f>] ? mntput_no_expire+0x3e/0x13d
[<ffffffff81117f33>] vfs_ioctl+0x18/0x34
[<ffffffff81118776>] do_vfs_ioctl+0x396/0x454
[<ffffffff81396b37>] ? sysret_check+0x1b/0x56
[<ffffffff81118886>] SyS_ioctl+0x52/0x7d
[<ffffffff81396b12>] system_call_fastpath+0x16/0x1b
2 locks held by kms_flip/14676:
#0: (&dev->mode_config.mutex){+.+.+.}, at: [<ffffffffa0316545>] drm_modeset_lock_all+0x22/0x59 [drm]
#1: (&crtc->mutex){+.+.+.}, at: [<ffffffffa031656b>] drm_modeset_lock_all+0x48/0x59 [drm]
INFO: task kworker/u8:4:175 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u8:4 D ffff88018de9a5c0 0 175 2 0x00000000
Workqueue: i915 i915_error_work_func [i915]
ffff88018e37dc30 0000000000000046 ffff8801938ab8a0 ffff88018e37dfd8
ffff88018e37dfd8 00000000001d3b00 ffff88018de9a5c0 ffff88018ec21018
0000000000000246 ffff88018e37dca0 000000005a865a86 ffff88018de9a5c0
Call Trace:
[<ffffffff8138ee7b>] schedule+0x60/0x62
[<ffffffff8138f23d>] schedule_preempt_disabled+0x9/0xb
[<ffffffff8138d0cd>] mutex_lock_nested+0x205/0x3b1
[<ffffffffa0477094>] ? intel_display_handle_reset+0x7e/0xbd [i915]
[<ffffffffa0477094>] ? intel_display_handle_reset+0x7e/0xbd [i915]
[<ffffffffa0477094>] intel_display_handle_reset+0x7e/0xbd [i915]
[<ffffffffa044e0a2>] i915_error_work_func+0x128/0x147 [i915]
[<ffffffff8104a89a>] process_one_work+0x1d4/0x35a
[<ffffffff8104a821>] ? process_one_work+0x15b/0x35a
[<ffffffff8104b4a5>] worker_thread+0x144/0x1f0
[<ffffffff8104b361>] ? rescuer_thread+0x275/0x275
[<ffffffff8105076d>] kthread+0xac/0xb4
[<ffffffff81059d30>] ? finish_task_switch+0x3b/0xc0
[<ffffffff810506c1>] ? __kthread_parkme+0x60/0x60
[<ffffffff81396a6c>] ret_from_fork+0x7c/0xb0
[<ffffffff810506c1>] ? __kthread_parkme+0x60/0x60
3 locks held by kworker/u8:4/175:
#0: (i915){.+.+.+}, at: [<ffffffff8104a821>] process_one_work+0x15b/0x35a
#1: ((&dev_priv->gpu_error.work)){+.+.+.}, at: [<ffffffff8104a821>] process_one_work+0x15b/0x35a
#2: (&crtc->mutex){+.+.+.}, at: [<ffffffffa0477094>] intel_display_handle_reset+0x7e/0xbd [i915]
This blew up while running kms_flip/flip-vs-panning-vs-hang-interruptible
on one of my older machines.
Unfortunately (despite the proper lockdep annotations for
flush_workqueue) lockdep still doesn't detect this correctly, so we
need to rely on chance to discover these bugs.
Apply the usual bugfix and schedule the reset work on the system
workqueue to keep our own driver workqueue free of any modeset lock
grabbing.
Note that this is not a terribly serious regression since before the
offending commit we'd simply have stalled userspace forever due to
failing to abort all outstanding pageflips.
v2: Add a comment as requested by Chris.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff 96a02917a0131e52efefde49c2784c0421d6c439 Mon Feb 18 11:08:49 CST 2013 Ville Syrjälä <ville.syrjala@linux.intel.com> drm/i915: Finish page flips and update primary planes after a GPU reset
GPU reset will drop all flips that are still in the ring. So after the
reset, call update_plane() for all CRTCs to make sure the primary
planes are scanning out from the correct buffer.
Also finish all pending flips. That means user space will get its
page flip events and won't get stuck waiting for them.
v2: Explicitly finish page flips instead of relying on FLIP_DONE
interrupt being generated by the base address update.
v3: Make two loops over crtcs to avoid deadlocks with the crtc mutex
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Fixup long line complaint from checkpatch.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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