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powerpc/perf: Invoke per-CPU variable access with disabled interrupts

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commit f66de7ac4849eb42a7b18e26b8ee49e08130fd27 upstream.

The power_pmu_event_init() callback access per-cpu variable
(cpu_hw_events) to check for event constraints and Branch Stack
(BHRB). Current usage is to disable preemption when accessing the
per-cpu variable, but this does not prevent timer callback from
interrupting event_init. Fix this by using 'local_irq_save/restore'
to make sure the code path is invoked with disabled interrupts.

This change is tested in mambo simulator to ensure that, if a timer
interrupt comes in during the per-cpu access in event_init, it will be
soft masked and replayed later. For testing purpose, introduced a
udelay() in power_pmu_event_init() to make sure a timer interrupt arrives
while in per-cpu variable access code between local_irq_save/resore.
As expected the timer interrupt was replayed later during local_irq_restore
called from power_pmu_event_init. This was confirmed by adding
breakpoint in mambo and checking the backtrace when timer_interrupt
was hit.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1606814880-1720-1-git-send-email-atrajeev@linux.vnet.ibm.com
Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Athira Rajeev 2020-12-01 04:28:00 -05:00 committed by AuxXxilium
parent 961d0fc60d
commit a687684df5
1 changed files with 6 additions and 4 deletions
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10
arch/powerpc/perf/core-book3s.c
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@ -1884,7 +1884,7 @@ static bool is_event_blacklisted(u64 ev)
static int power_pmu_event_init(struct perf_event *event)
{
u64 ev;
unsigned long flags;
unsigned long flags, irq_flags;
struct perf_event *ctrs[MAX_HWEVENTS];
u64 events[MAX_HWEVENTS];
unsigned int cflags[MAX_HWEVENTS];
@ -1992,7 +1992,9 @@ static int power_pmu_event_init(struct perf_event *event)
if (check_excludes(ctrs, cflags, n, 1))
return -EINVAL;
cpuhw = &get_cpu_var(cpu_hw_events);
local_irq_save(irq_flags);
cpuhw = this_cpu_ptr(&cpu_hw_events);
err = power_check_constraints(cpuhw, events, cflags, n + 1);
if (has_branch_stack(event)) {
@ -2003,13 +2005,13 @@ static int power_pmu_event_init(struct perf_event *event)
event->attr.branch_sample_type);
if (bhrb_filter == -1) {
put_cpu_var(cpu_hw_events);
local_irq_restore(irq_flags);
return -EOPNOTSUPP;
}
cpuhw->bhrb_filter = bhrb_filter;
}
put_cpu_var(cpu_hw_events);
local_irq_restore(irq_flags);
if (err)
return -EINVAL;