Regression: sched/preempt: Add static_key() to preempt_notifiers breaks my KVM

[Pontus Fuchs]

Hi,

On 4.1+ kernels I can no longer start my KVM guest. Upon trying to start 
it I can see the following log message:

[   25.821060] BUG: sleeping function called from invalid context at 
kernel/locking/mutex.c:97
[   25.821063] in_atomic(): 1, irqs_disabled(): 0, pid: 2113, name: 
qemu-system-x86
[   25.821066] CPU: 0 PID: 2113 Comm: qemu-system-x86 Not tainted 4.1.0+ #88
[   25.821067] Hardware name: Dell Inc.          Dell System XPS 
15Z/00WW5M, BIOS A12 09/07/2012
[   25.821068]  0000000000000061 ffff88021339bcd8 ffffffff816b8c81 
0000000000000007
[   25.821070]  ffff880231159d40 ffff88021339bcf8 ffffffff8107d163 
ffff88021339bd18
[   25.821072]  ffffffff81a451bc ffff88021339bd28 ffffffff8107d1ed 
ffff8802133a0000
[   25.821073] Call Trace:
[   25.821078]  [<ffffffff816b8c81>] dump_stack+0x4c/0x65
[   25.821081]  [<ffffffff8107d163>] ___might_sleep+0xd3/0x110
[   25.821083]  [<ffffffff8107d1ed>] __might_sleep+0x4d/0x90
[   25.821085]  [<ffffffff816bde74>] mutex_lock+0x24/0x50
[   25.821087]  [<ffffffff81141ef7>] static_key_slow_inc+0x57/0xc0
[   25.821089]  [<ffffffff8107cafd>] preempt_notifier_register+0x1d/0x60
[   25.821099]  [<ffffffffa04f11fd>] vcpu_load+0x3d/0x70 [kvm]
[   25.821108]  [<ffffffffa050699e>] kvm_arch_vcpu_setup+0x1e/0x50 [kvm]
[   25.821115]  [<ffffffffa05066e1>] ? kvm_arch_vcpu_create+0x51/0x70 [kvm]
[   25.821120]  [<ffffffffa04f29b2>] kvm_vm_ioctl+0x1d2/0x7a0 [kvm]
[   25.821123]  [<ffffffff811b7881>] do_vfs_ioctl+0x301/0x550
[   25.821124]  [<ffffffff811b7b49>] SyS_ioctl+0x79/0x90
[   25.821127]  [<ffffffff816c0257>] entry_SYSCALL_64_fastpath+0x12/0x6a

The offending commit is

commit 1cde2930e15473cb4dd7e5a07d83e605a969bd6e
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date:   Mon Jun 8 16:00:30 2015 +0200

    sched/preempt: Add static_key() to preempt_notifiers


BR,

Pontus Fuchs
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