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Subject[PATCH 6/7] clocksource/arm_arch_timer: Remove use of workaround static key
Date
The use of a static key in a hotplug path has proved to be a real
nightmare, and makes it impossible to have scream-free lockdep
kernel.

Let's remove the static key altogether, and focus on something saner.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/include/asm/arch_timer.h | 4 ----
drivers/clocksource/arm_arch_timer.c | 25 +++++++------------------
2 files changed, 7 insertions(+), 22 deletions(-)

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 4a06d46def7e..5502ea049b63 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -45,13 +45,9 @@
(__wa && __wa->h) ? __wa->h : arch_timer_##h; \
})

-extern struct static_key_false arch_timer_read_ool_enabled;
-#define needs_unstable_timer_counter_workaround() \
- static_branch_unlikely(&arch_timer_read_ool_enabled)
#else
#define has_erratum_handler(h) false
#define erratum_handler(h) (arch_timer_##h)
-#define needs_unstable_timer_counter_workaround() false
#endif

enum arch_timer_erratum_match_type {
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index c7f5b66d893c..da487fbfada3 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -372,8 +372,6 @@ static u32 notrace sun50i_a64_read_cntv_tval_el0(void)
DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *, timer_unstable_counter_workaround);
EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);

-DEFINE_STATIC_KEY_FALSE(arch_timer_read_ool_enabled);
-EXPORT_SYMBOL_GPL(arch_timer_read_ool_enabled);

static void erratum_set_next_event_tval_generic(const int access, unsigned long evt,
struct clock_event_device *clk)
@@ -552,12 +550,6 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa
per_cpu(timer_unstable_counter_workaround, i) = wa;
}

- /*
- * Use the locked version, as we're called from the CPU
- * hotplug framework. Otherwise, we end-up in deadlock-land.
- */
- static_branch_enable_cpuslocked(&arch_timer_read_ool_enabled);
-
/*
* Don't use the vdso fastpath if errata require using the
* out-of-line counter accessor. We may change our mind pretty
@@ -573,7 +565,7 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa
static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type type,
void *arg)
{
- const struct arch_timer_erratum_workaround *wa;
+ const struct arch_timer_erratum_workaround *wa, *__wa;
ate_match_fn_t match_fn = NULL;
bool local = false;

@@ -597,16 +589,13 @@ static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type t
if (!wa)
return;

- if (needs_unstable_timer_counter_workaround()) {
- const struct arch_timer_erratum_workaround *__wa;
- __wa = __this_cpu_read(timer_unstable_counter_workaround);
- if (__wa && wa != __wa)
- pr_warn("Can't enable workaround for %s (clashes with %s\n)",
- wa->desc, __wa->desc);
+ __wa = __this_cpu_read(timer_unstable_counter_workaround);
+ if (__wa && wa != __wa)
+ pr_warn("Can't enable workaround for %s (clashes with %s\n)",
+ wa->desc, __wa->desc);

- if (__wa)
- return;
- }
+ if (__wa)
+ return;

arch_timer_enable_workaround(wa, local);
pr_info("Enabling %s workaround for %s\n",
--
2.20.1
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