The idle_state entry in the PACA on PowerNV features a bit which is
atomically tested and set through ldarx/stdcx. to be used as a spinlock.
This lock then guards access to other bit fields of idle_state. KCSAN
cannot differentiate between any of these bitfield accesses as they all
are implemented by 8-byte store/load instructions, thus cores contending
on the bit-lock appear to data race with modifications to idle_state.
Separate the bit-lock entry from the data guarded by the lock to avoid
the possibility of data races being detected by KCSAN.
Suggested-by: Nicholas Piggin
Signed-off-by: Rohan McLure
---
v2: Remove extraneous WRITE_ONCE on paca thread_idle_state, which are
only read diagnostically.
---
arch/powerpc/include/asm/paca.h | 1 +
arch/powerpc/platforms/powernv/idle.c | 16 +---
2 files changed, 10 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index da0377f46597..cb325938766a 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -191,6 +191,7 @@ struct paca_struct {
#ifdef CONFIG_PPC_POWERNV
/* PowerNV idle fields */
/* PNV_CORE_IDLE_* bits, all siblings work on thread 0 paca */
+ unsigned long idle_lock; /* A value of 1 means acquired */
unsigned long idle_state;
union {
/* P7/P8 specific fields */
diff --git a/arch/powerpc/platforms/powernv/idle.c
b/arch/powerpc/platforms/powernv/idle.c
index 841cb7f31f4f..c1e0ecb014a5 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -246,9 +246,9 @@ static inline void atomic_lock_thread_idle(void)
{
int cpu = raw_smp_processor_id();
int first = cpu_first_thread_sibling(cpu);
- unsigned long *state = _ptrs[first]->idle_state;
+ unsigned long *lock = _ptrs[first]->idle_lock;
- while (unlikely(test_and_set_bit_lock(NR_PNV_CORE_IDLE_LOCK_BIT,
state)))
+ while (unlikely(test_and_set_bit_lock(NR_PNV_CORE_IDLE_LOCK_BIT, lock)))
barrier();
}
@@ -258,29 +258,31 @@ static inline void
atomic_unlock_and_stop_thread_idle(void)
int first = cpu_first_thread_sibling(cpu);
unsigned long thread = 1UL << cpu_thread_in_core(cpu);
unsigned long *state = _ptrs[first]->idle_state;
+ unsigned long *lock = _ptrs[first]->idle_lock;
u64 s = READ_ONCE(*state);
u64 new, tmp;
- BUG_ON(!(s & PNV_CORE_IDLE_LOCK_BIT));
+ BUG_ON(!(READ_ONCE(*lock) & PNV_CORE_IDLE_LOCK_BIT));
BUG_ON(s & thread);
again:
- new = (s | thread) & ~PNV_CORE_IDLE_LOCK_BIT;
+ new = s | thread;
tmp = cmpxchg(state, s, new);
if (unlikely(tmp != s)) {
s = tmp;
goto again;
}
+ clear_bit_unlock(NR_PNV_CORE_IDLE_LOCK_BIT, lock);
}
static inline void atomic_unlock_thread_idle(void)
{
int cpu = raw_smp_processor_id();
int first = cpu_first_thread_sibling(cpu);
- unsigned long *state = _ptrs[first]->idle_state;
+ unsigned long *lock = _ptrs[first]->idle_lock;
- BUG_ON(!test_bit(NR_PNV_CORE_IDLE_LOCK_BIT, state));
- clear_bit_unlock(NR_PNV_CORE_IDLE_LOCK_BIT, state);
+ BUG_ON(!test_bit(NR_PNV_CORE_IDLE_LOCK_BIT, lock));
+ clear_bit_unlock(NR_PNV_CORE_IDLE_LOCK_BIT, lock);
}
/* P7 and P8 */
--
2.37.2
