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Valentin Schneider 40fa3780ba sched/core: Take the hotplug lock in sched_init_smp() 
When running on linux-next (8c60c36d0b8c ("Add linux-next specific files
for 20181019")) + CONFIG_PROVE_LOCKING=y on a big.LITTLE system (e.g.
Juno or HiKey960), we get the following report:

 [    0.748225] Call trace:
 [    0.750685]  lockdep_assert_cpus_held+0x30/0x40
 [    0.755236]  static_key_enable_cpuslocked+0x20/0xc8
 [    0.760137]  build_sched_domains+0x1034/0x1108
 [    0.764601]  sched_init_domains+0x68/0x90
 [    0.768628]  sched_init_smp+0x30/0x80
 [    0.772309]  kernel_init_freeable+0x278/0x51c
 [    0.776685]  kernel_init+0x10/0x108
 [    0.780190]  ret_from_fork+0x10/0x18

The static_key in question is 'sched_asym_cpucapacity' introduced by
commit:

  df054e8445 ("sched/topology: Add static_key for asymmetric CPU capacity optimizations")

In this particular case, we enable it because smp_prepare_cpus() will
end up fetching the capacity-dmips-mhz entry from the devicetree,
so we already have some asymmetry detected when entering sched_init_smp().

This didn't get detected in tip/sched/core because we were missing:

  commit cb538267ea ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations")

Calls to build_sched_domains() post sched_init_smp() will hold the
hotplug lock, it just so happens that this very first call is a
special case. As stated by a comment in sched_init_smp(), "There's no
userspace yet to cause hotplug operations" so this is a harmless
warning.

However, to both respect the semantics of underlying
callees and make lockdep happy, take the hotplug lock in
sched_init_smp(). This also satisfies the comment atop
sched_init_domains() that says "Callers must hold the hotplug lock".

Reported-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dietmar.Eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: morten.rasmussen@arm.com
Cc: quentin.perret@arm.com
Link: http://lkml.kernel.org/r/1540301851-3048-1-git-send-email-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-11-04 00:57:44 +01:00
arch Merge branch 'akpm' (patches from Andrew) 2018-10-26 19:33:41 -07:00
block Merge branch 'akpm' (patches from Andrew) 2018-10-26 19:33:41 -07:00
certs
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2018-10-25 16:43:35 -07:00
Documentation Merge branch 'akpm' (patches from Andrew) 2018-10-26 19:33:41 -07:00
drivers i2c-hid: properly terminate i2c_hid_dmi_desc_override_table[] array 2018-10-27 09:10:48 -07:00
firmware
fs Merge branch 'akpm' (patches from Andrew) 2018-10-26 19:33:41 -07:00
include Merge branch 'akpm' (patches from Andrew) 2018-10-26 19:33:41 -07:00
init psi: cgroup support 2018-10-26 16:26:32 -07:00
ipc Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-10-25 11:14:36 -07:00
kernel sched/core: Take the hotplug lock in sched_init_smp() 2018-11-04 00:57:44 +01:00
lib Merge branch 'akpm' (patches from Andrew) 2018-10-26 19:33:41 -07:00
LICENSES
mm hugetlbfs: dirty pages as they are added to pagecache 2018-10-26 16:38:16 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-10-26 19:25:07 -07:00
samples Char/Misc driver patches for 4.20-rc1 2018-10-26 09:11:43 -07:00
scripts Merge branch 'akpm' (patches from Andrew) 2018-10-26 19:33:41 -07:00
security Merge branch 'next-loadpin' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2018-10-25 13:32:00 -07:00
sound sound updates for 4.20 2018-10-25 09:00:15 -07:00
tools Merge branch 'akpm' (patches from Andrew) 2018-10-26 19:33:41 -07:00
usr
virt Revert "mm, mmu_notifier: annotate mmu notifiers with blockable invalidate callbacks" 2018-10-26 16:25:19 -07:00
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MAINTAINERS Char/Misc driver patches for 4.20-rc1 2018-10-26 09:11:43 -07:00
Makefile Devicetree updates for 4.20: 2018-10-26 12:09:58 -07:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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There are various text files in the Documentation/ subdirectory,
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Please read the Documentation/process/changes.rst file, as it contains the
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