Greetings,

0day kernel testing robot got the below dmesg and the first bad commit is

https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/dev

commit 7d09545fc92f5db9fcb82a32ce1dc828f13a12bd
Author:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Wed Feb 15 21:33:48 2017 -0800
Commit:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
CommitDate: Wed Feb 15 21:33:48 2017 -0800

    rcu: Adjust rcu_do_batch() to allow finer-grained debugging
    
    This commit adds four helper functions for rcu_do_batch() in order to
    eliminate the time period when the rcu_segcblist structure would be
    malformed.  This malformation is due to the fact that all of the
    ready-to-invoke callbacks are extracted as a group, but that the counts
    are not adjusted until the full batch of callbacks are invoked.
    The reason for this is that it allows rcu_do_batch() to disable
    interrupts only twice instead of once per callback.  However, when
    debugging is enabled, we trade off a bit of performance to obtain
    more accurate debugging information.
    
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

+----------------------------------------------------+------------+------------+------------+
|                                                    | 86b66ae618 | 7d09545fc9 | 7d09545fc9 |
+----------------------------------------------------+------------+------------+------------+
| boot_successes                                     | 69         | 0          | 0          |
| boot_failures                                      | 0          | 43         | 43         |
| WARNING:at_kernel/rcu/tree.c:#rcu_do_batch_dequeue | 0          | 43         | 43         |
| BUG:kernel_hang_in_test_stage                      | 0          | 2          | 2          |
+----------------------------------------------------+------------+------------+------------+

[   12.781615] ppa0: failed to claim parport because a pardevice is owning the port for too long time!
[   12.784124] imm: Version 2.05 (for Linux 2.4.0)
[   12.801537] ------------[ cut here ]------------
[   12.802866] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree.c:2781 rcu_do_batch_dequeue+0x1f7/0x231
[   12.805645] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.10.0-rc3-00087-g7d09545 #580
[   12.807935] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-20161025_171302-gandalf 04/01/2014
[   12.810590] Call Trace:
[   12.811419]  <IRQ>
[   12.812283]  dump_stack+0x63/0x7f
[   12.813255]  __warn+0xbb/0xd6

git bisect start 7d09545fc92f5db9fcb82a32ce1dc828f13a12bd a121103c922847ba5010819a3f250f1f7fc84ab8 --
git bisect good c95c9aab351eb5963d86a67ed3f109ee8fc8f463  # 14:43     20+      0  rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle()
git bisect good 477663f4504298d63e838dd50164db682f71b6db  # 14:50     21+      0  fixup! rcu: Abstract multi-tail callback list handling
git bisect good 49c6fe3d43aad72f920b1b87a562b3a0f635eafb  # 14:52     21+      2  fixup! rcu: Abstract multi-tail callback list handling
git bisect good f09c1acfaa4b198694a31ba3e454c7d17c4fa680  # 14:54     22+      2  rcu: Add consistency checks for uses of segmented callback lists
git bisect good b3b0ab10a4ccb03ecb7cb3c3f39294e40640cabb  # 15:00     22+      0  fixup! rcu: Abstract multi-tail callback list handling
git bisect good 86b66ae6180c41682373b2250a344ce168063b08  # 15:06     20+      0  rcu: Add single-element dequeue functions to rcu_segcblist
# first bad commit: [7d09545fc92f5db9fcb82a32ce1dc828f13a12bd] rcu: Adjust rcu_do_batch() to allow finer-grained debugging
git bisect good 86b66ae6180c41682373b2250a344ce168063b08  # 15:09     63+      0  rcu: Add single-element dequeue functions to rcu_segcblist
# extra tests with CONFIG_DEBUG_INFO_REDUCED
git bisect  bad 7d09545fc92f5db9fcb82a32ce1dc828f13a12bd  # 15:17      0-     24  rcu: Adjust rcu_do_batch() to allow finer-grained debugging
# extra tests on HEAD of rcu/rcu/dev
git bisect  bad 7d09545fc92f5db9fcb82a32ce1dc828f13a12bd  # 15:17      0-     43  rcu: Adjust rcu_do_batch() to allow finer-grained debugging
# extra tests on tree/branch rcu/rcu/dev
git bisect  bad 7d09545fc92f5db9fcb82a32ce1dc828f13a12bd  # 15:17      0-     43  rcu: Adjust rcu_do_batch() to allow finer-grained debugging
# extra tests with first bad commit reverted
git bisect good 8a58c91e67e19918848a85e776d885eb37e0d6d5  # 15:31     61+      0  Revert "rcu: Adjust rcu_do_batch() to allow finer-grained debugging"
# extra tests on tree/branch linus/master
git bisect good 747ae0a96f1a78b35c5a3d93ad37a16655e16340  # 15:36     64+      7  Merge tag 'media/v4.10-4' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
# extra tests on tree/branch linux-next/master
git bisect good 38161d2f17e3f071418b1562e1bc57ad004d1244  # 15:41     64+     88  Add linux-next specific files for 20170216


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