powerpc/paravirt: correct preempt debug splat in vcpu_is_preempted()
vcpu_is_preempted() can be used outside of preempt-disabled critical sections, yielding warnings such as: BUG: using smp_processor_id() in preemptible [00000000] code: systemd-udevd/185 caller is rwsem_spin_on_owner+0x1cc/0x2d0 CPU: 1 PID: 185 Comm: systemd-udevd Not tainted 5.15.0-rc2+ #33 Call Trace: [c000000012907ac0] [c000000000aa30a8] dump_stack_lvl+0xac/0x108 (unreliable) [c000000012907b00] [c000000001371f70] check_preemption_disabled+0x150/0x160 [c000000012907b90] [c0000000001e0e8c] rwsem_spin_on_owner+0x1cc/0x2d0 [c000000012907be0] [c0000000001e1408] rwsem_down_write_slowpath+0x478/0x9a0 [c000000012907ca0] [c000000000576cf4] filename_create+0x94/0x1e0 [c000000012907d10] [c00000000057ac08] do_symlinkat+0x68/0x1a0 [c000000012907d70] [c00000000057ae18] sys_symlink+0x58/0x70 [c000000012907da0] [c00000000002e448] system_call_exception+0x198/0x3c0 [c000000012907e10] [c00000000000c54c] system_call_common+0xec/0x250 The result of vcpu_is_preempted() is always used speculatively, and the function does not access per-cpu resources in a (Linux) preempt-unsafe way. Use raw_smp_processor_id() to avoid such warnings, adding explanatory comments. Fixes: ca3f969d ("powerpc/paravirt: Use is_kvm_guest() in vcpu_is_preempted()") Signed-off-by:Nathan Lynch <nathanl@linux.ibm.com> Reviewed-by:
Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by:
Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20210928214147.312412-3-nathanl@linux.ibm.com
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799f9b51
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