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8231612: 100% cpu on arm32 in Service Thread

Reviewed-by: kbarrett, dsamersoff
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Aleksei Voitylov
Aleksei Voitylov committed Dec 13, 2019
1 parent 20b1410 commit 4d1176fd608497c8946cb986c8008a638c0c2c55
Showing with 26 additions and 9 deletions.
  1. +26 −9 src/hotspot/share/runtime/atomic.hpp
@@ -36,6 +36,7 @@
#include "metaprogramming/removePointer.hpp"
#include "runtime/orderAccess.hpp"
#include "utilities/align.hpp"
#include "utilities/bytes.hpp"
#include "utilities/macros.hpp"

enum atomic_memory_order {
@@ -578,6 +579,8 @@ struct Atomic::PlatformCmpxchg {
// as a base class, requiring it be complete. The definition is later
// in this file, near the other definitions related to cmpxchg.
struct Atomic::CmpxchgByteUsingInt {
static uint8_t get_byte_in_int(uint32_t n, uint32_t idx);
static uint32_t set_byte_in_int(uint32_t n, uint8_t b, uint32_t idx);
template<typename T>
T operator()(T volatile* dest,
T compare_value,
@@ -845,6 +848,19 @@ inline T Atomic::cmpxchg_using_helper(Fn fn,
PrimitiveConversions::cast<Type>(compare_value)));
}

inline uint32_t Atomic::CmpxchgByteUsingInt::set_byte_in_int(uint32_t n,
uint8_t b,
uint32_t idx) {
int bitsIdx = BitsPerByte * idx;
return (n & ~(0xff << bitsIdx)) | (b << bitsIdx);
}

inline uint8_t Atomic::CmpxchgByteUsingInt::get_byte_in_int(uint32_t n,
uint32_t idx) {
int bitsIdx = BitsPerByte * idx;
return (uint8_t)(n >> bitsIdx);
}

template<typename T>
inline T Atomic::CmpxchgByteUsingInt::operator()(T volatile* dest,
T compare_value,
@@ -856,20 +872,21 @@ inline T Atomic::CmpxchgByteUsingInt::operator()(T volatile* dest,
volatile uint32_t* aligned_dest
= reinterpret_cast<volatile uint32_t*>(align_down(dest, sizeof(uint32_t)));
size_t offset = pointer_delta(dest, aligned_dest, 1);
uint32_t cur = *aligned_dest;
uint8_t* cur_as_bytes = reinterpret_cast<uint8_t*>(&cur);

uint32_t idx = (Endian::NATIVE == Endian::BIG)
? (sizeof(uint32_t) - 1 - offset)
: offset;

// current value may not be what we are looking for, so force it
// to that value so the initial cmpxchg will fail if it is different
cur_as_bytes[offset] = canon_compare_value;
uint32_t cur = set_byte_in_int(Atomic::load(aligned_dest), canon_compare_value, idx);

// always execute a real cmpxchg so that we get the required memory
// barriers even on initial failure
do {
// value to swap in matches current value ...
uint32_t new_value = cur;
// ... except for the one byte we want to update
reinterpret_cast<uint8_t*>(&new_value)[offset] = canon_exchange_value;
// value to swap in matches current value
// except for the one byte we want to update
uint32_t new_value = set_byte_in_int(cur, canon_exchange_value, idx);

uint32_t res = cmpxchg(aligned_dest, cur, new_value, order);
if (res == cur) break; // success
@@ -878,9 +895,9 @@ inline T Atomic::CmpxchgByteUsingInt::operator()(T volatile* dest,
// our view of the current int
cur = res;
// if our byte is still as cur we loop and try again
} while (cur_as_bytes[offset] == canon_compare_value);
} while (get_byte_in_int(cur, idx) == canon_compare_value);

return PrimitiveConversions::cast<T>(cur_as_bytes[offset]);
return PrimitiveConversions::cast<T>(get_byte_in_int(cur, idx));
}

// Handle xchg for integral and enum types.

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