Bug 1884628 - Revert Bug 1853497, r=necko-reviewers,valentin

Differential Revision: https://phabricator.services.mozilla.com/D204199

netwerk/dns/nsDNSService2.cpp

@@ -1304,9 +1304,6 @@ nsDNSService::Observe(nsISupports* subject, const char* topic,
     nsAutoCString converted = NS_ConvertUTF16toUTF8(data);
     if (!strcmp(converted.get(), NS_NETWORK_LINK_DATA_CHANGED)) {
       flushCache = true;
-      if (mResolver) {
-        mResolver->ResetDNSConfigurations();
-      }
     }
   } else if (!strcmp(topic, "last-pb-context-exited")) {
     flushCache = true;

netwerk/dns/nsHostResolver.cpp

@@ -10,6 +10,7 @@
 #  include <arpa/inet.h>
 #  include <arpa/nameser.h>
 #  include <resolv.h>
+#  define RES_RETRY_ON_FAILURE
 #endif
 
 #include <stdlib.h>
@@ -44,9 +45,6 @@
 #include "mozilla/Telemetry.h"
 #include "mozilla/DebugOnly.h"
 #include "mozilla/Preferences.h"
-#if defined(HAVE_RES_NINIT)
-#  include "mozilla/RWLock.h"
-#endif
 #include "mozilla/StaticPrefs_network.h"
 // Put DNSLogging.h at the end to avoid LOG being overwritten by other headers.
 #include "DNSLogging.h"
@@ -100,6 +98,46 @@ LazyLogModule gHostResolverLog("nsHostResolver");
 
 //----------------------------------------------------------------------------
 
+#if defined(RES_RETRY_ON_FAILURE)
+
+// this class represents the resolver state for a given thread.  if we
+// encounter a lookup failure, then we can invoke the Reset method on an
+// instance of this class to reset the resolver (in case /etc/resolv.conf
+// for example changed).  this is mainly an issue on GNU systems since glibc
+// only reads in /etc/resolv.conf once per thread.  it may be an issue on
+// other systems as well.
+
+class nsResState {
+ public:
+  nsResState()
+      // initialize mLastReset to the time when this object
+      // is created.  this means that a reset will not occur
+      // if a thread is too young.  the alternative would be
+      // to initialize this to the beginning of time, so that
+      // the first failure would cause a reset, but since the
+      // thread would have just started up, it likely would
+      // already have current /etc/resolv.conf info.
+      : mLastReset(PR_IntervalNow()) {}
+
+  bool Reset() {
+    // reset no more than once per second
+    if (PR_IntervalToSeconds(PR_IntervalNow() - mLastReset) < 1) {
+      return false;
+    }
+
+    mLastReset = PR_IntervalNow();
+    auto result = res_ninit(&_res);
+
+    LOG(("nsResState::Reset() > 'res_ninit' returned %d", result));
+    return (result == 0);
+  }
+
+ private:
+  PRIntervalTime mLastReset;
+};
+
+#endif  // RES_RETRY_ON_FAILURE
+
 class DnsThreadListener final : public nsIThreadPoolListener {
   NS_DECL_THREADSAFE_ISUPPORTS
   NS_DECL_NSITHREADPOOLLISTENER
@@ -143,12 +181,6 @@ static void DnsPrefChanged(const char* aPref, void* aSelf) {
   }
 }
 
-#if defined(HAVE_RES_NINIT)
-static mozilla::StaticRWLock sGetAddrInfoLock;
-static mozilla::Atomic<bool, mozilla::Relaxed> sResInitCalled{false};
-static mozilla::Atomic<PRIntervalTime> sLastReset{PR_IntervalNow()};
-#endif
-
 NS_IMPL_ISUPPORTS0(nsHostResolver)
 
 nsHostResolver::nsHostResolver(uint32_t maxCacheEntries,
@@ -200,7 +232,8 @@ nsresult nsHostResolver::Init() MOZ_NO_THREAD_SAFETY_ANALYSIS {
   // during application startup.
   static int initCount = 0;
   if (initCount++ > 0) {
-    ResetDNSConfigurations();
+    auto result = res_ninit(&_res);
+    LOG(("nsHostResolver::Init > 'res_ninit' returned %d", result));
   }
 #endif
 
@@ -245,43 +278,6 @@ nsresult nsHostResolver::Init() MOZ_NO_THREAD_SAFETY_ANALYSIS {
   return NS_OK;
 }
 
-#if defined(HAVE_RES_NINIT)
-static void DoResetDNSConfigurations() {
-  // reset no more than once per second
-  if (PR_IntervalToSeconds(PR_IntervalNow() - sLastReset) < 1) {
-    return;
-  }
-
-  sLastReset = PR_IntervalNow();
-
-  StaticAutoWriteLock lock(sGetAddrInfoLock);
-  if (sResInitCalled) {
-    res_nclose(&_res);
-    sResInitCalled = false;
-  }
-
-  auto result = res_ninit(&_res);
-  LOG(("DoResetDNSConfigurations 'res_ninit' returned %d", result));
-  if (result == 0) {
-    sResInitCalled = true;
-  }
-}
-#endif
-
-void nsHostResolver::ResetDNSConfigurations() {
-#if defined(HAVE_RES_NINIT)
-  LOG(("nsHostResolver::ResetDNSConfigurations"));
-  if (NS_IsMainThread()) {
-    NS_DispatchBackgroundTask(
-        NS_NewRunnableFunction("nsHostResolver::ResetDNSConfigurations",
-                               []() { DoResetDNSConfigurations(); }));
-    return;
-  }
-
-  DoResetDNSConfigurations();
-#endif
-}
-
 void nsHostResolver::ClearPendingQueue(
     LinkedList<RefPtr<nsHostRecord>>& aPendingQ) {
   // loop through pending queue, erroring out pending lookups.
@@ -1807,18 +1803,12 @@ size_t nsHostResolver::SizeOfIncludingThis(MallocSizeOf mallocSizeOf) const {
   return n;
 }
 
-#if defined(HAVE_RES_NINIT)
-static nsresult GetAddrInfoLocked(const nsACString& aHost,
-                                  uint16_t aAddressFamily, uint16_t aFlags,
-                                  AddrInfo** aAddrInfo, bool aGetTtl) {
-  StaticAutoReadLock lock(sGetAddrInfoLock);
-  return GetAddrInfo(aHost, aAddressFamily, aFlags, aAddrInfo, aGetTtl);
-}
-#endif
-
 void nsHostResolver::ThreadFunc() {
   LOG(("DNS lookup thread - starting execution.\n"));
 
+#if defined(RES_RETRY_ON_FAILURE)
+  nsResState rs;
+#endif
   RefPtr<nsHostRecord> rec;
   RefPtr<AddrInfo> ai;
 
@@ -1858,12 +1848,13 @@ void nsHostResolver::ThreadFunc() {
       continue;
     }
 
-#if defined(HAVE_RES_NINIT)
-    nsresult status = GetAddrInfoLocked(rec->host, rec->af, rec->flags,
-                                        getter_AddRefs(ai), getTtl);
-#else
     nsresult status =
         GetAddrInfo(rec->host, rec->af, rec->flags, getter_AddRefs(ai), getTtl);
+#if defined(RES_RETRY_ON_FAILURE)
+    if (NS_FAILED(status) && rs.Reset()) {
+      status = GetAddrInfo(rec->host, rec->af, rec->flags, getter_AddRefs(ai),
+                           getTtl);
+    }
 #endif
 
     mozilla::glean::networking::dns_native_count

netwerk/dns/nsHostResolver.h

@@ -222,8 +222,6 @@ class nsHostResolver : public nsISupports, public AHostResolver {
   // available/enabled.
   bool TRRServiceEnabledForRecord(nsHostRecord* aRec) MOZ_REQUIRES(mLock);
 
-  void ResetDNSConfigurations();
-
  private:
   explicit nsHostResolver(uint32_t maxCacheEntries,
                           uint32_t defaultCacheEntryLifetime,