crash-reporter: Generate kernel crash signatures for server-side grouping of similar crashes

kernel_collector.cc

Index: kernel_collector.cc
diff --git a/kernel_collector.cc b/kernel_collector.cc
index c6bb33fca4d3c664edfd1e688e3a851466d29a5b..a95d757dbbaffe2ba423fcd0ac796a4c10e0a876 100644
--- a/kernel_collector.cc
+++ b/kernel_collector.cc
@@ -9,12 +9,21 @@
 #include "base/string_util.h"
 #include "crash-reporter/system_logging.h"
 
+const char KernelCollector::kClearingSequence[] = " ";
+static const char kDefaultKernelStackSignature[] =
+    "kernel-UnspecifiedStackSignature";
 static const char kKernelExecName[] = "kernel";
-static const char kPreservedDumpPath[] = "/sys/kernel/debug/preserved/kcrash";
 const pid_t kKernelPid = 0;
+static const char kKernelSignatureKey[] = "sig";
+// Byte length of maximum human readable portion of a kernel crash signature.
+static const int kMaxHumanStringLength = 40;
+static const char kPreservedDumpPath[] = "/sys/kernel/debug/preserved/kcrash";
 const uid_t kRootUid = 0;
-
-const char KernelCollector::kClearingSequence[] = " ";
+// Time in seconds from the final kernel log message for a call stack
+// to count towards the signature of the kcrash.
+static const int kSignatureTimestampWindow = 2;
+// Kernel log timestamp regular expression.
+static const std::string kTimestampRegex("^<.*>\\[\\s*(\\d+\\.\\d+)\\]");
 
 KernelCollector::KernelCollector()
     : is_enabled_(false),
@@ -66,6 +75,171 @@ bool KernelCollector::ClearPreservedDump() {
   return true;
 }
 
+// Hash a string to a number.  We define our own hash function to not
+// be dependent on a C++ library that might change.  This function
+// uses basically the same approach as tr1/functional_hash.h but with
+// a larger prime number (16127 vs 131).
+static unsigned HashString(const std::string &input) {
+  unsigned hash = 0;
+  for (size_t i = 0; i < input.length(); ++i)
+    hash = hash * 16127 + input[i];
+  return hash;
+}
+
+void KernelCollector::ProcessStackTrace(
+    pcrecpp::StringPiece kernel_dump,
+    bool print_diagnostics,
+    unsigned *hash,
+    float *last_stack_timestamp) {
+  pcrecpp::RE line_re("(.+)", pcrecpp::MULTILINE());
+  pcrecpp::RE stack_trace_start_re(kTimestampRegex + " Call Trace:$");
+  // Match lines such as the following and grab out "error_code".
+  // <4>[ 6066.849504]  [<7937bcee>] error_code+0x66/0x6c
+  pcrecpp::RE stack_entry_re(kTimestampRegex +
+                             "  \\[<.*>\\]([\\s\\?]+)([^\\+ ]+)");
+  std::string line;
+  std::string hashable;
+
+  *hash = 0;
+  *last_stack_timestamp = 0;
+
+  while (line_re.FindAndConsume(&kernel_dump, &line)) {
+    std::string certainty;
+    std::string function_name;
+    if (stack_trace_start_re.PartialMatch(line, last_stack_timestamp)) {
+      if (print_diagnostics) {
+        printf("Stack trace starting. Clearing any prior traces.\n");
+      }
+      hashable.clear();
+    } else if (stack_entry_re.PartialMatch(line,
+                                           last_stack_timestamp,
+                                           &certainty,
+                                           &function_name)) {
+      bool is_certain = certainty.find('?') == std::string::npos;
+      if (print_diagnostics) {
+        printf("@%f: stack entry for %s (%s)\n",
+               *last_stack_timestamp,
+               function_name.c_str(),
+               is_certain ? "certain" : "uncertain");
+      }
+      // Do not include any uncertain (prefixed by '?') frames in our hash.
+      if (!is_certain)
+        continue;
+      if (!hashable.empty())
+        hashable.append("|");
+      hashable.append(function_name);
+    }
+  }
+
+  *hash = HashString(hashable);
+
+  if (print_diagnostics) {
+    printf("Hash based on stack trace: \"%s\" at %f.\n",
+           hashable.c_str(), *last_stack_timestamp);
+  }
+}
+
+bool KernelCollector::FindCrashingFunction(
+    pcrecpp::StringPiece kernel_dump,
+    bool print_diagnostics,
+    float stack_trace_timestamp,
+    std::string *crashing_function) {
+  pcrecpp::RE eip_re(kTimestampRegex + " EIP: \\[<.*>\\] ([^\\+ ]+).*",
+                     pcrecpp::MULTILINE());
+  float timestamp = 0;
+  while (eip_re.FindAndConsume(&kernel_dump, &timestamp, crashing_function)) {
+    if (print_diagnostics) {
+      printf("@%f: found crashing function %s\n",
+             timestamp,
+             crashing_function->c_str());
+    }
+  }
+  if (timestamp == 0) {
+    if (print_diagnostics) {
+      printf("Found no crashing function.\n");
+    }
+    return false;
+  }
+  if (stack_trace_timestamp != 0 &&
+      abs(stack_trace_timestamp - timestamp) > kSignatureTimestampWindow) {
+    if (print_diagnostics) {
+      printf("Found crashing function but not within window.\n");
+    }
+    return false;
+  }
+  if (print_diagnostics) {
+    printf("Found crashing function %s\n", crashing_function->c_str());
+  }
+  return true;
+}
+
+bool KernelCollector::FindPanicMessage(pcrecpp::StringPiece kernel_dump,
+                                       bool print_diagnostics,
+                                       std::string *panic_message) {
+  // Match lines such as the following and grab out "Fatal exception"
+  // <0>[  342.841135] Kernel panic - not syncing: Fatal exception
+  pcrecpp::RE kernel_panic_re(kTimestampRegex +
+                              " Kernel panic[^\\:]*\\:\\s*(.*)",
+                              pcrecpp::MULTILINE());
+  float timestamp = 0;
+  while (kernel_panic_re.FindAndConsume(&kernel_dump,
+                                        &timestamp,
+                                        panic_message)) {
+    if (print_diagnostics) {
+      printf("@%f: panic message %s\n",
+             timestamp,
+             panic_message->c_str());
+    }
+  }
+  if (timestamp == 0) {
+    if (print_diagnostics) {
+      printf("Found no panic message.\n");
+    }
+    return false;
+  }
+  return true;
+}
+
+bool KernelCollector::ComputeKernelStackSignature(
+    const std::string &kernel_dump,
+    std::string *kernel_signature,
+    bool print_diagnostics) {
+  unsigned stack_hash = 0;
+  float last_stack_timestamp = 0;
+  std::string human_string;
+
+  ProcessStackTrace(kernel_dump,
+                    print_diagnostics,
+                    &stack_hash,
+                    &last_stack_timestamp);
+
+  if (!FindCrashingFunction(kernel_dump,
+                            print_diagnostics,
+                            last_stack_timestamp,
+                            &human_string)) {
+    if (!FindPanicMessage(kernel_dump, print_diagnostics, &human_string)) {
+      if (print_diagnostics) {
+        printf("Found no human readable string, using empty string.\n");
+      }
+      human_string.clear();
+    }
+  }
+
+  if (human_string.empty() && stack_hash == 0) {
+    if (print_diagnostics) {
+      printf("Found neither a stack nor a human readable string, failing.\n");
+    }
+    return false;
+  }
+
+  human_string = human_string.substr(0, kMaxHumanStringLength);
+  *kernel_signature = StringPrintf("%s-%s-%08X",
+                                   kKernelExecName,
+                                   human_string.c_str(),
+                                   stack_hash);
+  return true;
+}
+
 bool KernelCollector::Collect() {
   std::string kernel_dump;
   FilePath root_crash_directory;
@@ -75,9 +249,19 @@ bool KernelCollector::Collect() {
   if (kernel_dump.empty()) {
     return false;
   }
-  logger_->LogInfo("Received prior crash notification from kernel");
+  std::string signature;
+  if (!ComputeKernelStackSignature(kernel_dump, &signature, false)) {
+    signature = kDefaultKernelStackSignature;
+  }
+
+  bool feedback = is_feedback_allowed_function_();
+
+  logger_->LogInfo("Received prior crash notification from "
+                   "kernel (signature %s) (%s)",
+                   signature.c_str(),
+                   feedback ? "handling" : "ignoring");
 
-  if (is_feedback_allowed_function_()) {
+  if (feedback) {
     count_crash_function_();
 
     if (!GetCreatedCrashDirectoryByEuid(kRootUid,
@@ -101,16 +285,15 @@ bool KernelCollector::Collect() {
       return true;
     }
 
+    AddCrashMetaData(kKernelSignatureKey, signature);
     WriteCrashMetaData(
         root_crash_directory.Append(
             StringPrintf("%s.meta", dump_basename.c_str())),
         kKernelExecName,
         kernel_crash_path.value());
 
-    logger_->LogInfo("Collected kernel crash diagnostics into %s",
+    logger_->LogInfo("Stored kcrash to %s",
                      kernel_crash_path.value().c_str());
-  } else {
-    logger_->LogInfo("Crash not saved since metrics disabled");
   }
   if (!ClearPreservedDump()) {
     return false;