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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> |
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| .. | ||
| boot | ||
| configs | ||
| crypto | ||
| include | ||
| kernel | ||
| kvm | ||
| lib | ||
| math-emu | ||
| mm | ||
| net | ||
| oprofile | ||
| perf | ||
| platforms | ||
| sysdev | ||
| xmon | ||
| Kconfig | ||
| Kconfig.debug | ||
| Makefile | ||
| relocs_check.pl | ||