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The paravit queued spinlock slow path adds itself to the queue then
calls pv_wait to wait for the lock to become free. This is implemented
by calling H_CONFER to donate cycles.
When hcall tracing is enabled, this H_CONFER call can lead to a spin
lock being taken in the tracing code, which will result in the lock to
be taken again, which will also go to the slow path because it queues
behind itself and so won't ever make progress.
An example trace of a deadlock:
__pv_queued_spin_lock_slowpath
trace_clock_global
ring_buffer_lock_reserve
trace_event_buffer_lock_reserve
trace_event_buffer_reserve
trace_event_raw_event_hcall_exit
__trace_hcall_exit
plpar_hcall_norets_trace
__pv_queued_spin_lock_slowpath
trace_clock_global
ring_buffer_lock_reserve
trace_event_buffer_lock_reserve
trace_event_buffer_reserve
trace_event_raw_event_rcu_dyntick
rcu_irq_exit
irq_exit
__do_irq
call_do_irq
do_IRQ
hardware_interrupt_common_virt
Fix this by introducing plpar_hcall_norets_notrace(), and using that to
make SPLPAR virtual processor dispatching hcalls by the paravirt
spinlock code.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210508101455.1578318-2-npiggin@gmail.com
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