* DevNotes: Add entry cgf-000019.
* dcrt0.cc (do_exit): Just set exit_state to ES_EVENTS_TERMINATE and nuke call to events_terminate which just set a superfluous flag. * sigproc.cc (signal_exit_code): New variable. (setup_signal_exit): Define new function. (_cygtls::signal_exit): Remove accommodations for closing the signal pipe handle. (exit_thread): Just sleep if we're exiting. (wait_sig): If signal_exit_code is set, just handle bookkeeping signals and exit ReadFile loop if there is nothing more to process. Call signal_exit at end if signal_exit_code is non-zero. * sigproc.h (setup_signal_exit): Declare new function. * exceptions.cc (sigpacket::process): Use setup_signal_exit to control exiting due to a signal. (exception::handle): Ditto. Query exit_state rather than defunct exit_already to determine if we are exiting. * globals.cc (ES_SIGNAL_EXIT): New enum. * sync.h (lock_process::release): New function for explicitly unlocking muto. (lock_process::~lock_process): Use release method.
This commit is contained in:
Christopher Faylor
parent
81f1868336
commit
871d0724fa
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@ -1,3 +1,26 @@
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2012-12-28 Christopher Faylor <me.cygwin2012@cgf.cx>
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* DevNotes: Add entry cgf-000019.
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* dcrt0.cc (do_exit): Just set exit_state to ES_EVENTS_TERMINATE and
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nuke call to events_terminate which just set a superfluous flag.
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* sigproc.cc (signal_exit_code): New variable.
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(setup_signal_exit): Define new function.
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(_cygtls::signal_exit): Remove accommodations for closing the signal
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pipe handle.
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(exit_thread): Just sleep if we're exiting.
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(wait_sig): If signal_exit_code is set, just handle bookkeeping signals
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and exit ReadFile loop if there is nothing more to process. Call
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signal_exit at end if signal_exit_code is non-zero.
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* sigproc.h (setup_signal_exit): Declare new function.
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* exceptions.cc (sigpacket::process): Use setup_signal_exit to control
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exiting due to a signal.
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(exception::handle): Ditto. Query exit_state rather than defunct
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exit_already to determine if we are exiting.
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* globals.cc (ES_SIGNAL_EXIT): New enum.
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* sync.h (lock_process::release): New function for explicitly unlocking
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muto.
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(lock_process::~lock_process): Use release method.
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2012-12-27 Christopher Faylor <me.cygwin2012@cgf.cx>
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* fork.cc (child_info::prefork): Fix error message formatting.
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@ -1,3 +1,32 @@
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2012-12-28 cgf-000019
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(I forgot to mention that cgf-000018 was reverted. Although I never saw
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a hang from this, I couldn't convince myself that one wasn't possible.)
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This fix attempts to correct a deadlock where, when a true Windows
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signal arrives, Windows creates a thread which "does stuff" and attempts
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to exit. In the process of exiting Cygwin grabs the process lock. If
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the signal thread has seen the signal and wants to exit, it can't
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because the newly-created thread now holds it. But, since the new
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thread is relying on the signal thread to release its process lock,
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it exits and the process lock is never released.
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To fix this, I removed calls to _cygtls::signal_exit in favor of
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flagging that we were exiting by setting signal_exit_code (almost forgot
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to mark that NO_COPY: that would have been fun). The new function
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setup_signal_exit() now handles setting things up so that ReadFile loop
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in wait_sig will do the right thing when it terminates. This function
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may just Sleep indefinitely if a signal is being sent from a thread
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other than the signal thread. wait_sig() was changed so that it will
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essentially drop into asychronous-read-mode when a signal which exits
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has been detected. The ReadFile loop is exited when we know that the
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process is supposed to be exiting and there is nothing else in the
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signal queue.
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Although I never actually saw this happen, exit_thread() was also
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changed to release the process lock and just sleep indefintely if it is
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detected that we are exiting.
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2012-12-21 cgf-000018
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Re: cgf-000017
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@ -1098,10 +1098,7 @@ do_exit (int status)
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lock_process until_exit (true);
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if (exit_state < ES_EVENTS_TERMINATE)
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{
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exit_state = ES_EVENTS_TERMINATE;
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events_terminate ();
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}
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if (exit_state < ES_SIGNAL)
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{
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@ -41,8 +41,6 @@ static BOOL WINAPI ctrl_c_handler (DWORD);
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/* This is set to indicate that we have already exited. */
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static NO_COPY int exit_already = 0;
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NO_COPY static struct
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{
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unsigned int code;
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@ -481,9 +479,9 @@ exception::handle (EXCEPTION_RECORD *e, exception_list *frame, CONTEXT *in, void
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return 0;
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}
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/* If we've already exited, don't do anything here. Returning 1
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/* If we're exiting, don't do anything here. Returning 1
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tells Windows to keep looking for an exception handler. */
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if (exit_already || e->ExceptionFlags)
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if (exit_state || e->ExceptionFlags)
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return 1;
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siginfo_t si = {0};
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@ -673,8 +671,7 @@ exception::handle (EXCEPTION_RECORD *e, exception_list *frame, CONTEXT *in, void
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error_code);
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}
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/* Flag signal + core dump */
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me.signal_exit ((cygheap->rlim_core > 0UL ? 0x80 : 0) | si.si_signo);
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setup_signal_exit ((cygheap->rlim_core > 0UL ? 0x80 : 0) | si.si_signo);
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}
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si.si_addr = (si.si_signo == SIGSEGV || si.si_signo == SIGBUS
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@ -1249,13 +1246,9 @@ done:
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return rc;
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exit_sig:
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tls->signal_exit (si.si_signo); /* never returns */
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}
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void
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events_terminate ()
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{
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exit_already = 1;
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sigproc_printf ("setting up for exit with signal %d", si.si_signo);
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setup_signal_exit (si.si_signo);
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return rc;
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}
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int
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@ -34,6 +34,7 @@ UINT system_wow64_directory_length;
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enum exit_states
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{
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ES_NOT_EXITING = 0,
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ES_SIGNAL_EXIT,
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ES_EXIT_STARTING,
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ES_PROCESS_LOCKED,
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ES_EVENTS_TERMINATE,
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@ -61,6 +61,7 @@ _cygtls NO_COPY *_sig_tls;
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Static HANDLE my_sendsig;
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Static HANDLE my_readsig;
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Static int signal_exit_code;
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/* Function declarations */
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static int __stdcall checkstate (waitq *) __attribute__ ((regparm (1)));
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@ -361,32 +362,12 @@ close_my_readsig ()
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ForceCloseHandle1 (h, my_readsig);
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}
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/* Cover function to `do_exit' to handle exiting even in presence of more
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exceptions. We used to call exit, but a SIGSEGV shouldn't cause atexit
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routines to run. */
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/* Exit due to a signal, even in presence of more exceptions. We used to just
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call exit, but a SIGSEGV shouldn't cause atexit routines to run.
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Should only be called from the signal thread. */
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void
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_cygtls::signal_exit (int rc)
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{
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HANDLE myss = my_sendsig;
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my_sendsig = NULL; /* Make no_signals_allowed return true */
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/* This code used to try to always close my_readsig but it ended up
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blocking for reasons that people in google think make sense.
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It's possible that it was blocking because ReadFile was still active
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but it isn't clear why this only caused random hangs rather than
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consistent hangs. So, for now at least, avoid closing my_readsig
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unless this is the signal thread. */
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if (&_my_tls == _sig_tls)
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close_my_readsig (); /* Stop any currently executing sig_sends */
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else
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{
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sigpacket sp = {};
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sp.si.si_signo = __SIGEXIT;
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DWORD len;
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/* Write a packet to the wait_sig thread which tells it to exit and
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close my_readsig. */
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WriteFile (myss, &sp, sizeof (sp), &len, NULL);
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}
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signal_debugger (rc & 0x7f);
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if (rc == SIGQUIT || rc == SIGABRT)
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@ -553,6 +534,27 @@ sigproc_terminate (exit_states es)
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}
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}
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/* Set up stuff so that the signal thread will know that we are
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exiting due to a signal. */
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void
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setup_signal_exit (int sig)
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{
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signal_exit_code = sig; /* Tell wait_sig() that we are exiting. */
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exit_state = ES_SIGNAL_EXIT; /* Tell the rest of the world that we are exiting. */
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if (&_my_tls != _sig_tls)
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{
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sigpacket sp = {};
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sp.si.si_signo = __SIGEXIT;
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DWORD len;
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/* Write a packet to the wait_sig thread. It will eventuall cause
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the process to exit too. So just wait for that to happen after
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sending the packet. */
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WriteFile (my_sendsig, &sp, sizeof (sp), &len, NULL);
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Sleep (INFINITE);
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}
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}
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/* Exit the current thread very carefully.
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See cgf-000017 in DevNotes for more details on why this is
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necessary. */
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@ -576,10 +578,16 @@ exit_thread (DWORD res)
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siginfo_t si = {__SIGTHREADEXIT, SI_KERNEL};
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si.si_value.sival_ptr = h;
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lock_process for_now; /* May block indefinitely if we're exiting. */
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if (exit_state)
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{
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for_now.release ();
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Sleep (INFINITE);
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}
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/* Tell wait_sig to wait for this thread to exit. It can then release
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the lock below and close the above-opened handle. */
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sig_send (myself_nowait, si, &_my_tls);
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ExitThread (0); /* Should never hit this */
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ExitThread (0);
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}
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int __stdcall
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@ -1368,6 +1376,7 @@ pending_signals::next ()
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static void WINAPI
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wait_sig (VOID *)
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{
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extern int signal_exit_code;
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_sig_tls = &_my_tls;
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sig_hold = CreateEvent (&sec_none_nih, FALSE, FALSE, NULL);
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@ -1380,7 +1389,14 @@ wait_sig (VOID *)
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{
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if (pack.si.si_signo == __SIGHOLD)
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WaitForSingleObject (sig_hold, INFINITE);
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DWORD nb;
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/* If signal_exit_code is set then we are shutting down due to a signal.
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We'll exit this loop iff there is nothing more in the signal queue. */
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if (signal_exit_code
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&& (!PeekNamedPipe (my_readsig, NULL, 0, NULL, &nb, NULL) || !nb))
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break;
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pack.sigtls = NULL;
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if (!ReadFile (my_readsig, &pack, sizeof (pack), &nb, NULL))
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break;
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@ -1400,6 +1416,9 @@ wait_sig (VOID *)
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continue;
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}
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if (signal_exit_code && pack.si.si_signo > 0)
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continue; /* No more real signals allowed */
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sigset_t dummy_mask;
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if (!pack.mask)
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{
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@ -1505,8 +1524,14 @@ wait_sig (VOID *)
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break;
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}
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close_my_readsig ();
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sigproc_printf ("signal thread exiting");
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my_sendsig = NULL; /* Make no_signals_allowed return true */
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close_my_readsig (); /* Cause any sig_send's to stop */
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if (signal_exit_code)
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_my_tls.signal_exit (signal_exit_code);
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/* Just wait for the process to go away. Otherwise, this thread's
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exit value could be interpreted as the process exit value.
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See cgf-000017 in DevNotes for more details. */
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@ -89,6 +89,7 @@ void __stdcall sigalloc ();
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int kill_pgrp (pid_t, siginfo_t&);
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int killsys (pid_t, int);
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void exit_thread (DWORD) __attribute__ ((regparm (1), noreturn));
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void setup_signal_exit (int) __attribute__ ((regparm (1)));
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extern "C" void sigdelayed ();
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@ -55,10 +55,15 @@ public:
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if (exiting && exit_state < ES_PROCESS_LOCKED)
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exit_state = ES_PROCESS_LOCKED;
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}
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void release ()
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{
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locker.release ();
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skip_unlock = true;
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}
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~lock_process ()
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{
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if (!skip_unlock)
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locker.release ();
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release ();
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}
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static void force_release (_cygtls *tid) {locker.release (tid);}
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friend class dtable;
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