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Paul Mackerras 8f902b005e KVM: PPC: Book3S HV: Fix spinlock/mutex ordering issue in kvmppc_set_lpcr() 
Currently, kvmppc_set_lpcr() has a spinlock around the whole function,
and inside that does mutex_lock(&kvm->lock).  It is not permitted to
take a mutex while holding a spinlock, because the mutex_lock might
call schedule().  In addition, this causes lockdep to warn about a
lock ordering issue:

======================================================
[ INFO: possible circular locking dependency detected ]
3.18.0-kvm-04645-gdfea862-dirty #131 Not tainted
-------------------------------------------------------
qemu-system-ppc/8179 is trying to acquire lock:
 (&kvm->lock){+.+.+.}, at: [<d00000000ecc1f54>] .kvmppc_set_lpcr+0xf4/0x1c0 [kvm_hv]

but task is already holding lock:
 (&(&vcore->lock)->rlock){+.+...}, at: [<d00000000ecc1ea0>] .kvmppc_set_lpcr+0x40/0x1c0 [kvm_hv]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&(&vcore->lock)->rlock){+.+...}:
       [<c000000000b3c120>] .mutex_lock_nested+0x80/0x570
       [<d00000000ecc7a14>] .kvmppc_vcpu_run_hv+0xc4/0xe40 [kvm_hv]
       [<d00000000eb9f5cc>] .kvmppc_vcpu_run+0x2c/0x40 [kvm]
       [<d00000000eb9cb24>] .kvm_arch_vcpu_ioctl_run+0x54/0x160 [kvm]
       [<d00000000eb94478>] .kvm_vcpu_ioctl+0x4a8/0x7b0 [kvm]
       [<c00000000026cbb4>] .do_vfs_ioctl+0x444/0x770
       [<c00000000026cfa4>] .SyS_ioctl+0xc4/0xe0
       [<c000000000009264>] syscall_exit+0x0/0x98

-> #0 (&kvm->lock){+.+.+.}:
       [<c0000000000ff28c>] .lock_acquire+0xcc/0x1a0
       [<c000000000b3c120>] .mutex_lock_nested+0x80/0x570
       [<d00000000ecc1f54>] .kvmppc_set_lpcr+0xf4/0x1c0 [kvm_hv]
       [<d00000000ecc510c>] .kvmppc_set_one_reg_hv+0x4dc/0x990 [kvm_hv]
       [<d00000000eb9f234>] .kvmppc_set_one_reg+0x44/0x330 [kvm]
       [<d00000000eb9c9dc>] .kvm_vcpu_ioctl_set_one_reg+0x5c/0x150 [kvm]
       [<d00000000eb9ced4>] .kvm_arch_vcpu_ioctl+0x214/0x2c0 [kvm]
       [<d00000000eb940b0>] .kvm_vcpu_ioctl+0xe0/0x7b0 [kvm]
       [<c00000000026cbb4>] .do_vfs_ioctl+0x444/0x770
       [<c00000000026cfa4>] .SyS_ioctl+0xc4/0xe0
       [<c000000000009264>] syscall_exit+0x0/0x98

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&(&vcore->lock)->rlock);
                               lock(&kvm->lock);
                               lock(&(&vcore->lock)->rlock);
  lock(&kvm->lock);

 *** DEADLOCK ***

2 locks held by qemu-system-ppc/8179:
 #0:  (&vcpu->mutex){+.+.+.}, at: [<d00000000eb93f18>] .vcpu_load+0x28/0x90 [kvm]
 #1:  (&(&vcore->lock)->rlock){+.+...}, at: [<d00000000ecc1ea0>] .kvmppc_set_lpcr+0x40/0x1c0 [kvm_hv]

stack backtrace:
CPU: 4 PID: 8179 Comm: qemu-system-ppc Not tainted 3.18.0-kvm-04645-gdfea862-dirty #131
Call Trace:
[c000001a66c0f310] [c000000000b486ac] .dump_stack+0x88/0xb4 (unreliable)
[c000001a66c0f390] [c0000000000f8bec] .print_circular_bug+0x27c/0x3d0
[c000001a66c0f440] [c0000000000fe9e8] .__lock_acquire+0x2028/0x2190
[c000001a66c0f5d0] [c0000000000ff28c] .lock_acquire+0xcc/0x1a0
[c000001a66c0f6a0] [c000000000b3c120] .mutex_lock_nested+0x80/0x570
[c000001a66c0f7c0] [d00000000ecc1f54] .kvmppc_set_lpcr+0xf4/0x1c0 [kvm_hv]
[c000001a66c0f860] [d00000000ecc510c] .kvmppc_set_one_reg_hv+0x4dc/0x990 [kvm_hv]
[c000001a66c0f8d0] [d00000000eb9f234] .kvmppc_set_one_reg+0x44/0x330 [kvm]
[c000001a66c0f960] [d00000000eb9c9dc] .kvm_vcpu_ioctl_set_one_reg+0x5c/0x150 [kvm]
[c000001a66c0f9f0] [d00000000eb9ced4] .kvm_arch_vcpu_ioctl+0x214/0x2c0 [kvm]
[c000001a66c0faf0] [d00000000eb940b0] .kvm_vcpu_ioctl+0xe0/0x7b0 [kvm]
[c000001a66c0fcb0] [c00000000026cbb4] .do_vfs_ioctl+0x444/0x770
[c000001a66c0fd90] [c00000000026cfa4] .SyS_ioctl+0xc4/0xe0
[c000001a66c0fe30] [c000000000009264] syscall_exit+0x0/0x98

This fixes it by moving the mutex_lock()/mutex_unlock() pair outside
the spin-locked region.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
2015-03-20 11:41:14 +01:00
..
alpha asm-generic: uaccess.h cleanup 2015-02-18 10:02:24 -08:00
arc ARC: Fix thread_saved_pc() 2015-02-27 10:59:34 +05:30
arm Fixes for KVM/ARM for 4.0-rc5. 2015-03-16 20:08:56 -03:00
arm64 Fixes for KVM/ARM for 4.0-rc5. 2015-03-16 20:08:56 -03:00
avr32 asm-generic: uaccess.h cleanup 2015-02-18 10:02:24 -08:00
blackfin Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2015-02-21 12:59:04 -08:00
c6x all arches, signal: move restart_block to struct task_struct 2015-02-12 18:54:12 -08:00
cris CRIS changes for 3.20 2015-02-15 18:02:02 -08:00
frv mm: add missing __PAGETABLE_{PUD,PMD}_FOLDED defines 2015-02-28 09:57:51 -08:00
hexagon all arches, signal: move restart_block to struct task_struct 2015-02-12 18:54:12 -08:00
ia64 asm-generic: uaccess.h cleanup 2015-02-18 10:02:24 -08:00
m32r mm: add missing __PAGETABLE_{PUD,PMD}_FOLDED defines 2015-02-28 09:57:51 -08:00
m68k mm: add missing __PAGETABLE_{PUD,PMD}_FOLDED defines 2015-02-28 09:57:51 -08:00
metag metag: Fix KSTK_EIP() and KSTK_ESP() macros 2015-02-24 12:54:21 +00:00
microblaze all arches, signal: move restart_block to struct task_struct 2015-02-12 18:54:12 -08:00
mips KVM: MIPS: Enable after disabling interrupt 2015-03-02 19:18:12 -03:00
mn10300 mm: add missing __PAGETABLE_{PUD,PMD}_FOLDED defines 2015-02-28 09:57:51 -08:00
nios2 nios2 for v3.20 2015-02-17 14:23:42 -08:00
openrisc asm-generic: uaccess.h cleanup 2015-02-18 10:02:24 -08:00
parisc mm: add missing __PAGETABLE_{PUD,PMD}_FOLDED defines 2015-02-28 09:57:51 -08:00
powerpc KVM: PPC: Book3S HV: Fix spinlock/mutex ordering issue in kvmppc_set_lpcr() 2015-03-20 11:41:14 +01:00
s390 kvm: move advertising of KVM_CAP_IRQFD to common code 2015-03-10 21:18:59 -03:00
score all arches, signal: move restart_block to struct task_struct 2015-02-12 18:54:12 -08:00
sh asm-generic: uaccess.h cleanup 2015-02-18 10:02:24 -08:00
sparc asm-generic: uaccess.h cleanup 2015-02-18 10:02:24 -08:00
tile tile: use %*pb[l] to print bitmaps including cpumasks and nodemasks 2015-02-13 21:21:37 -08:00
um all arches, signal: move restart_block to struct task_struct 2015-02-12 18:54:12 -08:00
unicore32 mm: vmalloc: pass additional vm_flags to __vmalloc_node_range() 2015-02-13 21:21:42 -08:00
x86 KVM: VMX: Set msr bitmap correctly if vcpu is in guest mode 2015-03-13 09:24:51 -03:00
xtensa asm-generic: uaccess.h cleanup 2015-02-18 10:02:24 -08:00
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