After about 2 hours of firefox 99 running (was fine with earlier versions i.e.
98/etc.), the subthread known as "Netlink Monitor" in /proc/xxx/stat goes into
an infinite loop.

strace shows:

poll([{fd=22, events=POLLIN}, {fd=24, events=POLLIN}], 2, -1) = 1 ([{fd=24,
revents=POLLERR}])
poll([{fd=22, events=POLLIN}, {fd=24, events=POLLIN}], 2, -1) = 1 ([{fd=24,
revents=POLLERR}])
over and over again.

lsof:

firefox 30312 jengelh   22r     FIFO               0,13       0t0    4037553
pipe
firefox 30312 jengelh   24u  netlink                          0t0    4041789
ROUTE

gdb:

(gdb) bt
#0  0x00007f5c92e8052f in poll () at /lib64/libc.so.6
#1  0x00007f5c88c8d68b in poll () at /usr/include/bits/poll2.h:39
#2  operator() () at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/netwerk/system/netlink/NetlinkService.cpp:1205
#3  eintr_retry<mozilla::net::NetlinkService::Run()::<lambda()> > ()
    at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/netwerk/system/netlink/NetlinkService.cpp:45
#4  mozilla::net::NetlinkService::Run() () at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/netwerk/system/netlink/NetlinkService.cpp:1203
#5  0x00007f5c8882b4a5 in nsThread::ProcessNextEvent(bool, bool*) () at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/xpcom/threads/nsThread.cpp:1167
#6  0x00007f5c888043d8 in NS_ProcessNextEvent(nsIThread*, bool) () at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/xpcom/threads/nsThreadUtils.cpp:467
#7  0x00007f5c88d5ae0d in
mozilla::ipc::MessagePumpForNonMainThreads::Run(base::MessagePump::Delegate*)
()
    at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/ipc/glue/MessagePump.cpp:300
#8  0x00007f5c88d349b5 in MessageLoop::RunInternal() () at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/ipc/chromium/src/base/message_loop.cc:331
#9  MessageLoop::RunHandler() () at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/ipc/chromium/src/base/message_loop.cc:324
#10 MessageLoop::Run() () at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/ipc/chromium/src/base/message_loop.cc:306
#11 0x00007f5c888238c9 in nsThread::ThreadFunc(void*) () at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/xpcom/threads/nsThread.cpp:389
#12 0x00007f5c92c3e110 in  () at /lib64/libnspr4.so
#13 0x000055b617ce67ea in set_alt_signal_stack_and_start(PthreadCreateParams*)
()
    at
/usr/src/debug/MozillaFirefox-99.0.1-1.1.x86_64/toolkit/crashreporter/pthread_create_interposer/pthread_create_interposer.cpp:80
#14 0x00007f5c92e042ba in start_thread () at /lib64/libc.so.6
#15 0x00007f5c92e8e460 in clone3 () at /lib64/libc.so.6

code in question:

1193      while (!shutdown) {
1194        if (mOutgoingMessages.Length() &&
!mOutgoingMessages[0]->IsPending()) {
1195          if (!mOutgoingMessages[0]->Send(netlinkSocket)) {
1196            LOG(("Failed to send netlink message"));
1197            mOutgoingMessages.RemoveElementAt(0);
1198            // try to send another message if available before polling
1199            continue;
1200          }
1201        }
1202
1203        int rc = eintr_retry([&]() {
1204          AUTO_PROFILER_THREAD_SLEEP;
1205          return poll(fds, 2, GetPollWait());
1206        });
1207
1208        if (rc > 0) {
1209          if (fds[0].revents & POLLIN) {
1210            // shutdown, abort the loop!
1211            LOG(("thread shutdown received, dying...\n"));
1212            shutdown = true;
1213          } else if (fds[1].revents & POLLIN) {
1214            LOG(("netlink message received, handling it...\n"));
1215            OnNetlinkMessage(netlinkSocket);
1216          }
1217        } else if (rc < 0) {
1218          rv = NS_ERROR_FAILURE;
1219          break;
1220        }
1221      }

stepping and repetition pattern:

(gdb) n
1194        if (mOutgoingMessages.Length() &&
!mOutgoingMessages[0]->IsPending()) {
(gdb) 
1203        int rc = eintr_retry([&]() {
(gdb) 
1208        if (rc > 0) {
(gdb) 
1209          if (fds[0].revents & POLLIN) {
(gdb) 
1213          } else if (fds[1].revents & POLLIN) {
(gdb) 
1194        if (mOutgoingMessages.Length() &&
!mOutgoingMessages[0]->IsPending()) {

As shown above by strace, there's a POLLERR condition on the netlink socket,
and FF fails to handle it.