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SubjectPossible regression in 3.17-rc2 in i915 driver

I tried to upgrade my kernel from 3.16 to 3.17-rc2 and I found that my laptop
was unable to boot. The boot process hangs after 2-3 seconds (according to
timestamps of log messages). The last kernel log line I usually see is the
discovery of my touchpad: "input: SynPS/2 Synaptics TouchPad as

I did a git bisect and it pointed me to the following commit:
commit 208bf9fdcd3575aa4a5d48b3e0295f7cdaf6fc44
Author: Ville Syrjälä <>
Date:   Mon Aug 11 13:15:35 2014 +0300
    drm/i915: Fix locking for intel_enable_pipe_a()
    intel_enable_pipe_a() gets called with all the modeset locks already
    held (by drm_modeset_lock_all()), so trying to grab the same
    locks using another drm_modeset_acquire_ctx is going to fail miserably.
    Move most of the drm_modeset_acquire_ctx handling (init/drop/fini)
    out from intel_{get,release}_load_detect_pipe() into the callers
    (intel_{crt,tv}_detect()). Only the actual locking and backoff
    handling is left in intel_get_load_detect_pipe(). And in
    intel_enable_pipe_a() we just share the mode_config.acquire_ctx from
    drm_modeset_lock_all() which is already holding all the relevant locks.
    It's perfectly legal to lock the same ww_mutex multiple times using the
    same ww_acquire_ctx. drm_modeset_lock() will convert the returned
    -EALREADY into 0, so the caller doesn't need to do antyhing special.
    Fixes a hang on resume on my 830.
    Signed-off-by: Ville Syrjälä <>
    Reviewed-by: Daniel Vetter <>
    Signed-off-by: Jani Nikula <>
I tried booting with the above commit reverted on top of 3.17-rc2 and it
booted successfully.
I also did a MagicSyrq-W (Display list of blocked (D state) tasks) after the
boot process stopped (using plain 3.17-rc2, without reverting the above commit)
and it showed that plymouthd was blocked with the following call trace (hand
This may have something to do with the hang or it may not, I don't know but is
related to drm locking so I thought it was a good idea to mention it.
My laptop is an old Fujitsu-Siemens Amilo M1450g, running Linux Mint 16.
Let me know if I can help further debug this issue.
Tibor Billes
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