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
./arch/powerpc/include/asm/paravirt.h:83:44: error: implicit declaration
of function 'smp_processor_id'; did you mean 'raw_smp_processor_id'?
smp_processor_id is defined in linux/smp.h but it is not included.
The build error happens only when the patch is applied to 5.3 kernel but
it only works by chance in mainline.
Fixes: ca3f969dcb ("powerpc/paravirt: Use is_kvm_guest() in vcpu_is_preempted()")
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210120132838.15589-1-msuchanek@suse.de
This implements the generic paravirt qspinlocks using H_PROD and
H_CONFER to kick and wait.
This uses an un-directed yield to any CPU rather than the directed
yield to a pre-empted lock holder that paravirtualised simple
spinlocks use, that requires no kick hcall. This is something that
could be investigated and improved in future.
Performance results can be found in the commit which added queued
spinlocks.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200724131423.1362108-5-npiggin@gmail.com
These functions will be used by the queued spinlock implementation,
and may be useful elsewhere too, so move them out of spinlock.h.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200724131423.1362108-2-npiggin@gmail.com
Nicholas Piggin
Michal Suchanek
Srikar Dronamraju