zig/lib/tsan/tsan_sync.cpp

//===-- tsan_sync.cpp -----------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file is a part of ThreadSanitizer (TSan), a race detector.
//
//===----------------------------------------------------------------------===//
#include "sanitizer_common/sanitizer_placement_new.h"
#include "tsan_sync.h"
#include "tsan_rtl.h"
#include "tsan_mman.h"

namespace __tsan {

void DDMutexInit(ThreadState *thr, uptr pc, SyncVar *s);

SyncVar::SyncVar() : mtx(MutexTypeSyncVar) { Reset(0); }

void SyncVar::Init(ThreadState *thr, uptr pc, uptr addr, u64 uid) {
  this->addr = addr;
  this->uid = uid;
  this->next = 0;

  creation_stack_id = 0;
  if (!SANITIZER_GO)  // Go does not use them
    creation_stack_id = CurrentStackId(thr, pc);
  if (common_flags()->detect_deadlocks)
    DDMutexInit(thr, pc, this);
}

void SyncVar::Reset(Processor *proc) {
  uid = 0;
  creation_stack_id = 0;
  owner_tid = kInvalidTid;
  last_lock = 0;
  recursion = 0;
  atomic_store_relaxed(&flags, 0);

  if (proc == 0) {
    CHECK_EQ(clock.size(), 0);
    CHECK_EQ(read_clock.size(), 0);
  } else {
    clock.Reset(&proc->clock_cache);
    read_clock.Reset(&proc->clock_cache);
  }
}

MetaMap::MetaMap()
    : block_alloc_(LINKER_INITIALIZED, "heap block allocator"),
      sync_alloc_(LINKER_INITIALIZED, "sync allocator") {
  atomic_store(&uid_gen_, 0, memory_order_relaxed);
}

void MetaMap::AllocBlock(ThreadState *thr, uptr pc, uptr p, uptr sz) {
  u32 idx = block_alloc_.Alloc(&thr->proc()->block_cache);
  MBlock *b = block_alloc_.Map(idx);
  b->siz = sz;
  b->tag = 0;
  b->tid = thr->tid;
  b->stk = CurrentStackId(thr, pc);
  u32 *meta = MemToMeta(p);
  DCHECK_EQ(*meta, 0);
  *meta = idx | kFlagBlock;
}

uptr MetaMap::FreeBlock(Processor *proc, uptr p) {
  MBlock* b = GetBlock(p);
  if (b == 0)
    return 0;
  uptr sz = RoundUpTo(b->siz, kMetaShadowCell);
  FreeRange(proc, p, sz);
  return sz;
}

bool MetaMap::FreeRange(Processor *proc, uptr p, uptr sz) {
  bool has_something = false;
  u32 *meta = MemToMeta(p);
  u32 *end = MemToMeta(p + sz);
  if (end == meta)
    end++;
  for (; meta < end; meta++) {
    u32 idx = *meta;
    if (idx == 0) {
      // Note: don't write to meta in this case -- the block can be huge.
      continue;
    }
    *meta = 0;
    has_something = true;
    while (idx != 0) {
      if (idx & kFlagBlock) {
        block_alloc_.Free(&proc->block_cache, idx & ~kFlagMask);
        break;
      } else if (idx & kFlagSync) {
        DCHECK(idx & kFlagSync);
        SyncVar *s = sync_alloc_.Map(idx & ~kFlagMask);
        u32 next = s->next;
        s->Reset(proc);
        sync_alloc_.Free(&proc->sync_cache, idx & ~kFlagMask);
        idx = next;
      } else {
        CHECK(0);
      }
    }
  }
  return has_something;
}

// ResetRange removes all meta objects from the range.
// It is called for large mmap-ed regions. The function is best-effort wrt
// freeing of meta objects, because we don't want to page in the whole range
// which can be huge. The function probes pages one-by-one until it finds a page
// without meta objects, at this point it stops freeing meta objects. Because
// thread stacks grow top-down, we do the same starting from end as well.
void MetaMap::ResetRange(Processor *proc, uptr p, uptr sz) {
  if (SANITIZER_GO) {
    // UnmapOrDie/MmapFixedNoReserve does not work on Windows,
    // so we do the optimization only for C/C++.
    FreeRange(proc, p, sz);
    return;
  }
  const uptr kMetaRatio = kMetaShadowCell / kMetaShadowSize;
  const uptr kPageSize = GetPageSizeCached() * kMetaRatio;
  if (sz <= 4 * kPageSize) {
    // If the range is small, just do the normal free procedure.
    FreeRange(proc, p, sz);
    return;
  }
  // First, round both ends of the range to page size.
  uptr diff = RoundUp(p, kPageSize) - p;
  if (diff != 0) {
    FreeRange(proc, p, diff);
    p += diff;
    sz -= diff;
  }
  diff = p + sz - RoundDown(p + sz, kPageSize);
  if (diff != 0) {
    FreeRange(proc, p + sz - diff, diff);
    sz -= diff;
  }
  // Now we must have a non-empty page-aligned range.
  CHECK_GT(sz, 0);
  CHECK_EQ(p, RoundUp(p, kPageSize));
  CHECK_EQ(sz, RoundUp(sz, kPageSize));
  const uptr p0 = p;
  const uptr sz0 = sz;
  // Probe start of the range.
  for (uptr checked = 0; sz > 0; checked += kPageSize) {
    bool has_something = FreeRange(proc, p, kPageSize);
    p += kPageSize;
    sz -= kPageSize;
    if (!has_something && checked > (128 << 10))
      break;
  }
  // Probe end of the range.
  for (uptr checked = 0; sz > 0; checked += kPageSize) {
    bool has_something = FreeRange(proc, p + sz - kPageSize, kPageSize);
    sz -= kPageSize;
    // Stacks grow down, so sync object are most likely at the end of the region
    // (if it is a stack). The very end of the stack is TLS and tsan increases
    // TLS by at least 256K, so check at least 512K.
    if (!has_something && checked > (512 << 10))
      break;
  }
  // Finally, page out the whole range (including the parts that we've just
  // freed). Note: we can't simply madvise, because we need to leave a zeroed
  // range (otherwise __tsan_java_move can crash if it encounters a left-over
  // meta objects in java heap).
  uptr metap = (uptr)MemToMeta(p0);
  uptr metasz = sz0 / kMetaRatio;
  UnmapOrDie((void*)metap, metasz);
  if (!MmapFixedSuperNoReserve(metap, metasz))
    Die();
}

MBlock* MetaMap::GetBlock(uptr p) {
  u32 *meta = MemToMeta(p);
  u32 idx = *meta;
  for (;;) {
    if (idx == 0)
      return 0;
    if (idx & kFlagBlock)
      return block_alloc_.Map(idx & ~kFlagMask);
    DCHECK(idx & kFlagSync);
    SyncVar * s = sync_alloc_.Map(idx & ~kFlagMask);
    idx = s->next;
  }
}

SyncVar* MetaMap::GetOrCreateAndLock(ThreadState *thr, uptr pc,
                              uptr addr, bool write_lock) {
  return GetAndLock(thr, pc, addr, write_lock, true);
}

SyncVar* MetaMap::GetIfExistsAndLock(uptr addr, bool write_lock) {
  return GetAndLock(0, 0, addr, write_lock, false);
}

SyncVar *MetaMap::GetAndLock(ThreadState *thr, uptr pc, uptr addr, bool write_lock,
                             bool create) NO_THREAD_SAFETY_ANALYSIS {
  u32 *meta = MemToMeta(addr);
  u32 idx0 = *meta;
  u32 myidx = 0;
  SyncVar *mys = 0;
  for (;;) {
    u32 idx = idx0;
    for (;;) {
      if (idx == 0)
        break;
      if (idx & kFlagBlock)
        break;
      DCHECK(idx & kFlagSync);
      SyncVar * s = sync_alloc_.Map(idx & ~kFlagMask);
      if (s->addr == addr) {
        if (myidx != 0) {
          mys->Reset(thr->proc());
          sync_alloc_.Free(&thr->proc()->sync_cache, myidx);
        }
        if (write_lock)
          s->mtx.Lock();
        else
          s->mtx.ReadLock();
        return s;
      }
      idx = s->next;
    }
    if (!create)
      return 0;
    if (*meta != idx0) {
      idx0 = *meta;
      continue;
    }

    if (myidx == 0) {
      const u64 uid = atomic_fetch_add(&uid_gen_, 1, memory_order_relaxed);
      myidx = sync_alloc_.Alloc(&thr->proc()->sync_cache);
      mys = sync_alloc_.Map(myidx);
      mys->Init(thr, pc, addr, uid);
    }
    mys->next = idx0;
    if (atomic_compare_exchange_strong((atomic_uint32_t*)meta, &idx0,
        myidx | kFlagSync, memory_order_release)) {
      if (write_lock)
        mys->mtx.Lock();
      else
        mys->mtx.ReadLock();
      return mys;
    }
  }
}

void MetaMap::MoveMemory(uptr src, uptr dst, uptr sz) {
  // src and dst can overlap,
  // there are no concurrent accesses to the regions (e.g. stop-the-world).
  CHECK_NE(src, dst);
  CHECK_NE(sz, 0);
  uptr diff = dst - src;
  u32 *src_meta = MemToMeta(src);
  u32 *dst_meta = MemToMeta(dst);
  u32 *src_meta_end = MemToMeta(src + sz);
  uptr inc = 1;
  if (dst > src) {
    src_meta = MemToMeta(src + sz) - 1;
    dst_meta = MemToMeta(dst + sz) - 1;
    src_meta_end = MemToMeta(src) - 1;
    inc = -1;
  }
  for (; src_meta != src_meta_end; src_meta += inc, dst_meta += inc) {
    CHECK_EQ(*dst_meta, 0);
    u32 idx = *src_meta;
    *src_meta = 0;
    *dst_meta = idx;
    // Patch the addresses in sync objects.
    while (idx != 0) {
      if (idx & kFlagBlock)
        break;
      CHECK(idx & kFlagSync);
      SyncVar *s = sync_alloc_.Map(idx & ~kFlagMask);
      s->addr += diff;
      idx = s->next;
    }
  }
}

void MetaMap::OnProcIdle(Processor *proc) {
  block_alloc_.FlushCache(&proc->block_cache);
  sync_alloc_.FlushCache(&proc->sync_cache);
}

}  // namespace __tsan