linux.git/arch/powerpc/kernel/smp.c, branch v4.17

powerpc: Fix deadlock with multiple calls to smp_send_stop

2018-04-27T06:35:57+00:00

smp_send_stop can lock up the IPI path for any subsequent calls,
because the receiving CPUs spin in their handler function. This
started becoming a problem with the addition of an smp_send_stop
call in the reboot path, because panics can reboot after doing
their own smp_send_stop.

The NMI IPI variant was fixed with ac61c11566 ("powerpc: Fix
smp_send_stop NMI IPI handling"), which leaves the smp_call_function
variant.

This is fixed by having smp_send_stop only ever do the
smp_call_function once. This is a bit less robust than the NMI IPI
fix, because any other call to smp_call_function after smp_send_stop
could deadlock, but that has always been the case, and it was not
been a problem before.

Fixes: f2748bdfe1573 ("powerpc/powernv: Always stop secondaries before reboot/shutdown")
Reported-by: Abdul Haleem 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

powerpc: Fix smp_send_stop NMI IPI handling

2018-04-25T10:38:08+00:00

The NMI IPI handler for a receiving CPU increments nmi_ipi_busy_count
over the handler function call, which causes later smp_send_nmi_ipi()
callers to spin until the call is finished.

The stop_this_cpu() function never returns, so the busy count is never
decremeted, which can cause the system to hang in some cases. For
example panic() will call smp_send_stop() early on which calls
stop_this_cpu() on other CPUs, then later in the reboot path,
pnv_restart() will call smp_send_stop() again, which hangs.

Fix this by adding a special case to the stop_this_cpu() handler to
decrement the busy count, because it will never return.

Now that the NMI/non-NMI versions of stop_this_cpu() are different,
split them out into separate functions rather than doing #ifdef tricks
to share the body between the two functions.

Fixes: 6bed3237624e3 ("powerpc: use NMI IPI for smp_send_stop")
Reported-by: Abdul Haleem 
Signed-off-by: Nicholas Piggin 
[mpe: Split out the functions, tweak change log a bit]
Signed-off-by: Michael Ellerman

powerpc: hard disable irqs in smp_send_stop loop

2018-04-03T12:59:10+00:00

The hard lockup watchdog can fire under local_irq_disable
on platforms with irq soft masking.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

powerpc: use NMI IPI for smp_send_stop

2018-04-03T12:59:09+00:00

Use the NMI IPI rather than smp_call_function for smp_send_stop.
Have stopped CPUs hard disable interrupts rather than just soft
disable.

This function is used in crash/panic/shutdown paths to bring other
CPUs down as quickly and reliably as possible, and minimizing their
potential to cause trouble.

Avoiding the Linux smp_call_function infrastructure and (if supported)
using true NMI IPIs makes this more robust.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

powerpc/64: Use array of paca pointers and allocate pacas individually

2018-03-30T12:34:23+00:00

Change the paca array into an array of pointers to pacas. Allocate
pacas individually.

This allows flexibility in where the PACAs are allocated. Future work
will allocate them node-local. Platforms that don't have address limits
on PACAs would be able to defer PACA allocations until later in boot
rather than allocate all possible ones up-front then freeing unused.

This is slightly more overhead (one additional indirection) for cross
CPU paca references, but those aren't too common.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

powernv/kdump: Fix cases where the kdump kernel can get HMI's

2018-01-16T12:47:11+00:00

Certain HMI's such as malfunction error propagate through
all threads/core on the system. If a thread was offline
prior to us crashing the system and jumping to the kdump
kernel, bad things happen when it wakes up due to an HMI
in the kdump kernel.

There are several possible ways to solve this problem

1. Put the offline cores in a state such that they are
not woken up for machine check and HMI errors. This
does not work, since we might need to wake up offline
threads to handle TB errors
2. Ignore HMI errors, setup HMEER to mask HMI errors,
but this still leads the window open for any MCEs
and masking them for the duration of the dump might
be a concern
3. Wake up offline CPUs, as in send them to
crash_ipi_callback (not wake them up as in mark them
online as seen by the hotplug). kexec does a
wake_online_cpus() call, this patch does something
similar, but instead sends an IPI and forces them to
crash_ipi_callback()

This patch takes approach #3.

Care is taken to enable this only for powenv platforms
via crash_wake_offline (a global value set at setup
time). The crash code sends out IPI's to all CPU's
which then move to crash_ipi_callback and kexec_smp_wait().

Signed-off-by: Balbir Singh 
Reviewed-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

powerpc/smp: Add Power9 scheduler topology

2017-08-31T08:16:08+00:00

In previous generations of Power processors each core had a private L2
cache. The Power 9 processor has a slightly different design where the
L2 cache is shared among pairs of cores rather than being completely
private.

Making the scheduler aware of this cache sharing allows the scheduler to
make better migration decisions. For example, if two CPU heavy tasks
share a core then one task can be migrated to the paired core to improve
throughput. Under the existing three level topology the task could be
migrated to any core on the same chip, while with the new topology it
would be preferentially migrated to the paired core so it remains
cache-hot.

Signed-off-by: Oliver O'Halloran 
Signed-off-by: Michael Ellerman

powerpc/smp: Add cpu_l2_cache_map

2017-08-31T04:26:56+00:00

We want to add an extra level to the CPU scheduler topology to account
for cores which share a cache. To do this we need to build a cpumask
for each CPU that indicates which CPUs share this cache to use as an
input to the scheduler.

Signed-off-by: Oliver O'Halloran 
Signed-off-by: Michael Ellerman

powerpc/smp: Rework CPU topology construction

2017-08-31T04:26:51+00:00

The CPU scheduler topology is constructed from a number of per-cpu
cpumasks which describe which sets of logical CPUs are related in some
fashion. Current code that handles constructing these masks when CPUs
are hot(un)plugged can be simplified a bit by exploiting the fact that
the scheduler requires higher levels of the toplogy (e.g package level
groupings) to be supersets of the lower levels (e.g.  threas in a core).
This patch reworks the cpumask construction to be simpler and easier to
extend with extra topology levels.

Signed-off-by: Oliver O'Halloran 
[mpe: Fix CONFIG_HOTPLUG_CPU=n build]
Signed-off-by: Michael Ellerman

powerpc/smp: Use cpu_to_chip_id() to find core siblings

2017-08-31T04:26:50+00:00

When building the CPU scheduler topology the kernel uses the ibm,chipid
property from the devicetree to group logical CPUs. Currently the DT
search for this property is open-coded in smp.c and this functionality
is a duplication of what's in cpu_to_chip_id() already. This patch
removes the existing search in favor of that.

It's worth mentioning that the semantics of the search are different
in cpu_to_chip_id(). When there is no ibm,chipid in the CPUs node it
will also search /cpus and / for the property, but this should not
effect the output topology.

Signed-off-by: Oliver O'Halloran 
Signed-off-by: Michael Ellerman