[lsan] Add an interface function for on-demand leak checking.

[earthdok]

Summary

Add an interface function which can be used to periodically trigger
leak detection in a long-running process.

NB: The meaning of the kIgnored tag has been changed to allow easy clean-up
between subsequent leak checks. Previously, this tag was applied to explicitly
ignored (i.e. with lsan_disable() or lsan_ignore_object()) chunks *and* any
chunks only reachable from those. With this change, it's only applied to
explicitly ignored chunks.

[earthdok]

As always, I hate the name, so any suggestions are welcome.

[earthdok]

Incidentally this will call the summary callback every time leaks are detected. Do you foresee any problems with that?

[earthdok]

Our symbolization code still leaks. :( When I call this function in an infinite loop I observe a small but steady increase in memory usage (as shown by smem) - but only when symbolization is enabled.

[samsonov]

LGTM!

I think that printing SUMMARY multiple times is fine. We do this in both TSan and (recoverable) UBSan, for instance. Leaking symbolization is an issue... Let me know if you want to investigate it, or delegate it to me.

include/sanitizer/lsan_interface.h

61

Bikeshedding suggestion from me:

__lsan_do_recoverable_leak_check()

lib/lsan/lsan_common.cc

333

Add

void(arg)

to defeat unused-variable warning?

444

if (!have_leaks)
  return;
<more code>

[earthdok]

In D9159#159457, @samsonov wrote:

Leaking symbolization is an issue... Let me know if you want to investigate it, or delegate it to me.

Fixed in r235411

include/sanitizer/lsan_interface.h

61

I'll have to give this another thought before landing.

lib/lsan/lsan_common.cc

333

done

444

done

[earthdok]

• address comments

[samsonov]

OK, feel free to land when it's convenient for you.

[earthdok]

• change "extra" to "recoverable"

[earthdok]

Committed r235728

include/sanitizer/lsan_interface.h

#endif
   // - LSan will skip any inaccessible memory when scanning a root region. E.g.,
   // if you map memory within a larger region that you have mprotect'ed, you can
   // register the entire large region.
   // - the implementation is not optimized for performance. This interface is
   // intended to be used for a small number of relatively static regions.
   void __lsan_register_root_region(const void *p, size_t size);
   void __lsan_unregister_root_region(const void *p, size_t size);
 
-  // Calling this function makes LSan enter the leak checking phase immediately.
-  // Use this if normal end-of-process leak checking happens too late (e.g. if
-  // you have intentional memory leaks in your shutdown code). Calling this
-  // function overrides end-of-process leak checking; it must be called at
-  // most once per process. This function will terminate the process if there
-  // are memory leaks and the exit_code flag is non-zero.
+  // Check for leaks now. This function behaves identically to the default
+  // end-of-process leak check. In particular, it will terminate the process if
+  // leaks are found and the exit_code flag is non-zero.
+  // Subsequent calls to this function will have no effect and end-of-process
+  // leak check will not run. Effectively, end-of-process leak check is moved to
+  // the time of first invocation of this function.
+  // By calling this function early during process shutdown, you can instruct
+  // LSan to ignore shutdown-only leaks which happen later on.
   void __lsan_do_leak_check();
 
+  // Check for leaks now. Returns zero if no leaks have been found or if leak
+  // detection is disabled, non-zero otherwise.
+  // This function may be called repeatedly, e.g. to periodically check a
+  // long-running process. It prints a leak report if appropriate, but does not
+  // terminate the process. It does not affect the behavior of
+  // __lsan_do_leak_check() or the end-of-process leak check, and is not
+  // affected by them.
+  int __lsan_do_extra_leak_check();
+
   // The user may optionally provide this function to disallow leak checking
   // for the program it is linked into (if the return value is non-zero). This
   // function must be defined as returning a constant value; any behavior beyond
   // that is unsupported.
   int __lsan_is_turned_off();
 
   // This function may be optionally provided by the user and should return
   // a string containing LSan suppressions.

lib/lsan/lsan_common.cc

#elif defined(__mips64)
   return ((p >> 40) == 0);
 #else
   return true;
 #endif
 }
 
 // Scans the memory range, looking for byte patterns that point into allocator
 // chunks. Marks those chunks with |tag| and adds them to |frontier|.
-// There are two usage modes for this function: finding reachable or ignored
-// chunks (|tag| = kReachable or kIgnored) and finding indirectly leaked chunks
+// There are two usage modes for this function: finding reachable chunks
+// (|tag| = kReachable) and finding indirectly leaked chunks
 // (|tag| = kIndirectlyLeaked). In the second case, there's no flood fill,
 // so |frontier| = 0.
 void ScanRangeForPointers(uptr begin, uptr end,
                           Frontier *frontier,
                           const char *region_type, ChunkTag tag) {
+  CHECK(tag == kReachable || tag == kIndirectlyLeaked);
   const uptr alignment = flags()->pointer_alignment();
   LOG_POINTERS("Scanning %s range %p-%p.\n", region_type, begin, end);
   uptr pp = begin;
   if (pp % alignment)
     pp = pp + alignment - pp % alignment;
   for (; pp + sizeof(void *) <= end; pp += alignment) {  // NOLINT
     void *p = *reinterpret_cast<void **>(pp);
     if (!CanBeAHeapPointer(reinterpret_cast<uptr>(p))) continue;
     uptr chunk = PointsIntoChunk(p);
     if (!chunk) continue;
     // Pointers to self don't count. This matters when tag == kIndirectlyLeaked.
     if (chunk == begin) continue;
     LsanMetadata m(chunk);
-    // Reachable beats ignored beats leaked.
-    if (m.tag() == kReachable) continue;
-    if (m.tag() == kIgnored && tag != kReachable) continue;
+    if (m.tag() == kReachable || m.tag() == kIgnored) continue;
 
     // Do this check relatively late so we can log only the interesting cases.
     if (!flags()->use_poisoned && WordIsPoisoned(pp)) {
       LOG_POINTERS(
           "%p is poisoned: ignoring %p pointing into chunk %p-%p of size "
           "%zu.\n",
           pp, p, chunk, chunk + m.requested_size(), m.requested_size());
       continue;

 
 // ForEachChunk callback. If the chunk is marked as leaked, marks all chunks
 // which are reachable from it as indirectly leaked.
 static void MarkIndirectlyLeakedCb(uptr chunk, void *arg) {
   chunk = GetUserBegin(chunk);
   LsanMetadata m(chunk);
   if (m.allocated() && m.tag() != kReachable) {
     ScanRangeForPointers(chunk, chunk + m.requested_size(),
-                         /* frontier */ 0, "HEAP", kIndirectlyLeaked);
+                         /* frontier */ nullptr, "HEAP", kIndirectlyLeaked);
   }
 }
 
 // ForEachChunk callback. If chunk is marked as ignored, adds its address to
 // frontier.
 static void CollectIgnoredCb(uptr chunk, void *arg) {
   CHECK(arg);
   chunk = GetUserBegin(chunk);
   LsanMetadata m(chunk);
-  if (m.allocated() && m.tag() == kIgnored)
+  if (m.allocated() && m.tag() == kIgnored) {
+    LOG_POINTERS("Ignored: chunk %p-%p of size %zu.\n",
+                 chunk, chunk + m.requested_size(), m.requested_size());
     reinterpret_cast<Frontier *>(arg)->push_back(chunk);
   }
+}
 
 // Sets the appropriate tag on each chunk.
 static void ClassifyAllChunks(SuspendedThreadsList const &suspended_threads) {
   // Holds the flood fill frontier.
   Frontier frontier(1);
 
+  ForEachChunk(CollectIgnoredCb, &frontier);
   ProcessGlobalRegions(&frontier);
   ProcessThreads(suspended_threads, &frontier);
   ProcessRootRegions(&frontier);
   FloodFillTag(&frontier, kReachable);
+
   // The check here is relatively expensive, so we do this in a separate flood
   // fill. That way we can skip the check for chunks that are reachable
   // otherwise.
   LOG_POINTERS("Processing platform-specific allocations.\n");
+  CHECK_EQ(0, frontier.size());
   ProcessPlatformSpecificAllocations(&frontier);
   FloodFillTag(&frontier, kReachable);
 
-  LOG_POINTERS("Scanning ignored chunks.\n");
-  CHECK_EQ(0, frontier.size());
-  ForEachChunk(CollectIgnoredCb, &frontier);
-  FloodFillTag(&frontier, kIgnored);
-
   // Iterate over leaked chunks and mark those that are reachable from other
   // leaked chunks.
   LOG_POINTERS("Scanning leaked chunks.\n");
-  ForEachChunk(MarkIndirectlyLeakedCb, 0 /* arg */);
+  ForEachChunk(MarkIndirectlyLeakedCb, nullptr);
+}
+
+// ForEachChunk callback. Resets the tags to pre-leak-check state.
+static void ResetTagsCb(uptr chunk, void *arg) {
+  (void)arg;
+  chunk = GetUserBegin(chunk);
+  LsanMetadata m(chunk);
+  if (m.allocated() && m.tag() != kIgnored)
+    m.set_tag(kDirectlyLeaked);
 }
 
 static void PrintStackTraceById(u32 stack_trace_id) {
   CHECK(stack_trace_id);
   StackDepotGet(stack_trace_id).Print();
 }
 
 // ForEachChunk callback. Aggregates information about unreachable chunks into
static void PrintMatchedSuppressions() {
   Printf("Suppressions used:\n");
   Printf("  count      bytes template\n");
   for (uptr i = 0; i < matched.size(); i++)
     Printf("%7zu %10zu %s\n", static_cast<uptr>(matched[i]->hit_count),
            matched[i]->weight, matched[i]->templ);
   Printf("%s\n\n", line);
 }
 
-struct DoLeakCheckParam {
+struct CheckForLeaksParam {
   bool success;
   LeakReport leak_report;
 };
 
-static void DoLeakCheckCallback(const SuspendedThreadsList &suspended_threads,
+static void CheckForLeaksCallback(const SuspendedThreadsList &suspended_threads,
                                   void *arg) {
-  DoLeakCheckParam *param = reinterpret_cast<DoLeakCheckParam *>(arg);
+  CheckForLeaksParam *param = reinterpret_cast<CheckForLeaksParam *>(arg);
   CHECK(param);
   CHECK(!param->success);
   ClassifyAllChunks(suspended_threads);
   ForEachChunk(CollectLeaksCb, &param->leak_report);
+  // Clean up for subsequent leak checks. This assumes we did not overwrite any
+  // kIgnored tags.
+  ForEachChunk(ResetTagsCb, nullptr);
   param->success = true;
 }
 
-void DoLeakCheck() {
-  EnsureMainThreadIDIsCorrect();
-  BlockingMutexLock l(&global_mutex);
-  static bool already_done;
-  if (already_done) return;
-  already_done = true;
+static bool CheckForLeaks() {
   if (&__lsan_is_turned_off && __lsan_is_turned_off())
-      return;
-
-  DoLeakCheckParam param;
+      return false;
+  EnsureMainThreadIDIsCorrect();
+  CheckForLeaksParam param;
   param.success = false;
   LockThreadRegistry();
   LockAllocator();
-  DoStopTheWorld(DoLeakCheckCallback, &param);
+  DoStopTheWorld(CheckForLeaksCallback, &param);
   UnlockAllocator();
   UnlockThreadRegistry();
 
   if (!param.success) {
     Report("LeakSanitizer has encountered a fatal error.\n");
     Die();
   }
   param.leak_report.ApplySuppressions();
   uptr unsuppressed_count = param.leak_report.UnsuppressedLeakCount();
   if (unsuppressed_count > 0) {
     Decorator d;
     Printf("\n"
            "================================================================="
            "\n");
     Printf("%s", d.Error());
     Report("ERROR: LeakSanitizer: detected memory leaks\n");
     Printf("%s", d.End());
     param.leak_report.ReportTopLeaks(flags()->max_leaks);
   }
   if (common_flags()->print_suppressions)
     PrintMatchedSuppressions();
   if (unsuppressed_count > 0) {
     param.leak_report.PrintSummary();
-    if (flags()->exitcode) {
-      if (common_flags()->coverage)
-        __sanitizer_cov_dump();
-      internal__exit(flags()->exitcode);
-    }
-  }
+    return true;
+  }
+  return false;
+}
+
+void DoLeakCheck() {
+  BlockingMutexLock l(&global_mutex);
+  static bool already_done;
+  if (already_done) return;
+  already_done = true;
+  bool have_leaks = CheckForLeaks();
+  if (!have_leaks) {
+    return;
+  }
+
+static int DoExtraLeakCheck() {
+  BlockingMutexLock l(&global_mutex);
+  bool have_leaks = CheckForLeaks();
+  return have_leaks ? 1 : 0;
 }
 
 static Suppression *GetSuppressionForAddr(uptr addr) {
   Suppression *s = nullptr;
 
   // Suppress by module name.
   SuppressionContext *suppressions = GetSuppressionContext();
   if (const char *module_name =

 SANITIZER_INTERFACE_ATTRIBUTE
 void __lsan_do_leak_check() {
 #if CAN_SANITIZE_LEAKS
   if (common_flags()->detect_leaks)
     __lsan::DoLeakCheck();
 #endif  // CAN_SANITIZE_LEAKS
 }
 
+int __lsan_do_extra_leak_check() {
+#if CAN_SANITIZE_LEAKS
+  if (common_flags()->detect_leaks)
+    return __lsan::DoExtraLeakCheck();
+#endif  // CAN_SANITIZE_LEAKS
+  return 0;
+}
+
 #if !SANITIZER_SUPPORTS_WEAK_HOOKS
 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
 int __lsan_is_turned_off() {
   return 0;
 }
 #endif
 }  // extern "C"

lib/lsan/lsan_common_linux.cc

 // ForEachChunk callback. Identifies unreachable chunks which must be treated as
 // reachable. Marks them as reachable and adds them to the frontier.
 static void ProcessPlatformSpecificAllocationsCb(uptr chunk, void *arg) {
   CHECK(arg);
   ProcessPlatformAllocParam *param =
       reinterpret_cast<ProcessPlatformAllocParam *>(arg);
   chunk = GetUserBegin(chunk);
   LsanMetadata m(chunk);
-  if (m.allocated() && m.tag() != kReachable) {
+  if (m.allocated() && m.tag() != kReachable && m.tag() != kIgnored) {
     u32 stack_id = m.stack_trace_id();
     uptr caller_pc = 0;
     if (stack_id > 0)
       caller_pc = GetCallerPC(stack_id, param->stack_depot_reverse_map);
     // If caller_pc is unknown, this chunk may be allocated in a coroutine. Mark
     // it as reachable, as we can't properly report its allocation stack anyway.
     if (caller_pc == 0 || linker->containsAddress(caller_pc)) {
       m.set_tag(kReachable);

test/lsan/TestCases/extra_leak_check.cc

+// Test for on-demand leak checking.
+// RUN: LSAN_BASE="use_stacks=0:use_registers=0"
+// RUN: %clangxx_lsan %s -o %t
+// RUN: LSAN_OPTIONS=$LSAN_BASE %run %t foo 2>&1 | FileCheck %s
+// RUN: LSAN_OPTIONS=$LSAN_BASE %run %t 2>&1 | FileCheck %s
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sanitizer/lsan_interface.h>
+
+void *p;
+
+int main(int argc, char *argv[]) {
+  p = malloc(23);
+
+  assert(__lsan_do_extra_leak_check() == 0);
+
+  fprintf(stderr, "Test alloc: %p.\n", malloc(1337));
+// CHECK: Test alloc:
+
+  assert(__lsan_do_extra_leak_check() == 1);
+// CHECK: SUMMARY: {{(Leak|Address)}}Sanitizer: 1337 byte
+
+  // Test that we correctly reset chunk tags.
+  p = 0;
+  assert(__lsan_do_extra_leak_check() == 1);
+// CHECK: SUMMARY: {{(Leak|Address)}}Sanitizer: 1360 byte
+
+  _exit(0);
+}