[patch] Fix SIGTERM signal safety (PR gdb/15358)

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

gdb deadlock due to gdb calling calloc() in signal handler
http://sourceware.org/bugzilla/show_bug.cgi?id=15358

Patch depends in its functionality on:
	[patchv2 2/2] Fix CTRL-C for remote.c (PR remote/15297)
	http://sourceware.org/ml/gdb-patches/2013-06/msg00943.html
	Message-ID: <20130630181110.GB29548@host2.jankratochvil.net>

async mode seems easy.

The sync mode is a bit difficult - assuming it is safe to call quit_force from
any place of QUIT;.  OTOH the patch above assumes it can do:
	  if (check_quit_flag ())
	    send_interrupt_sequence ();
which clears quit_flag but we used set_quit_flag () to call quit_force, not
just to throw the quit exception.  This is why QUIT now checks also for
SYNC_QUIT_FORCE_RUN.

The change in linux-nat.c comes from testing i386-linux-nat.c (therefore
32-bit host GDB).  i386_linux_resume there calls QUIT; via target_read ().
This is a bug on its own, filed as:
	http://sourceware.org/bugzilla/show_bug.cgi?id=15713

But I have seen another bug in linux-nat.c, it was depending on PTRACE_KILL
but at least Linux kernel ptrace expert Oleg Nesterov considers PTRACE_KILL
superseded by kill(SIGKILL).  Therefore I used there (also) more safe SIGKILL 
so that the possibly inconsistent state of inferior from i386_linux_resume
does not matter.


No regressions on {x86_64,x86_64-m32,i686}-fedora19pre-linux-gnu and in
gdbserver mode.


Thanks,
Jan


gdb/
2013-07-02  Jan Kratochvil  <jan.kratochvil@redhat.com>

	PR gdb/15358
	* defs.h (sync_quit_force_run): New declaration.
	(QUIT): Check also SYNC_QUIT_FORCE_RUN.
	* event-top.c (async_sigterm_handler): New declaration.
	(async_sigterm_token): New variable.
	(async_init_signals): Create also async_sigterm_token.
	(async_sigterm_handler): New function.
	(sync_quit_force_run): New variable.
	(handle_sigterm): Replace quit_force call by other calls.
	* linux-nat.c (linux_nat_kill): Use kill_callback first.
	Extend the comment for stop_callback.
	* utils.c (quit): Call quit_force if SYNC_QUIT_FORCE_RUN.

gdb/testsuite/
2013-07-02  Jan Kratochvil  <jan.kratochvil@redhat.com>

	PR gdb/15358
	* gdb.base/gdb-sigterm.c: New file.
	* gdb.base/gdb-sigterm.exp: New file.

diff --git a/gdb/defs.h b/gdb/defs.h
index d8a1adb..1807167 100644
--- a/gdb/defs.h
+++ b/gdb/defs.h
@@ -176,6 +176,9 @@ extern int check_quit_flag (void);
 /* Set the quit flag.  */
 extern void set_quit_flag (void);
 
+/* Flag that function quit should call quit_force.  */
+extern volatile int sync_quit_force_run;
+
 extern int immediate_quit;
 
 extern void quit (void);
@@ -188,7 +191,7 @@ extern void quit (void);
    needed.  */
 
 #define QUIT { \
-  if (check_quit_flag ()) quit (); \
+  if (check_quit_flag () || sync_quit_force_run) quit (); \
   if (deprecated_interactive_hook) deprecated_interactive_hook (); \
 }
 
diff --git a/gdb/event-top.c b/gdb/event-top.c
index f00ab7d..4e9aa4d 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -72,6 +72,7 @@ static void async_float_handler (gdb_client_data);
 #ifdef STOP_SIGNAL
 static void async_stop_sig (gdb_client_data);
 #endif
+static void async_sigterm_handler (gdb_client_data arg);
 
 /* Readline offers an alternate interface, via callback
    functions.  These are all included in the file callback.c in the
@@ -135,6 +136,7 @@ static struct async_signal_handler *sigfpe_token;
 #ifdef STOP_SIGNAL
 static struct async_signal_handler *sigtstp_token;
 #endif
+static struct async_signal_handler *async_sigterm_token;
 
 /* Structure to save a partially entered command.  This is used when
    the user types '\' at the end of a command line.  This is necessary
@@ -769,6 +771,8 @@ async_init_signals (void)
     create_async_signal_handler (async_stop_sig, NULL);
 #endif
 
+  async_sigterm_token =
+    create_async_signal_handler (async_sigterm_handler, NULL);
 }
 
 /* Tell the event loop what to do if SIGINT is received.
@@ -796,13 +800,31 @@ handle_sigint (int sig)
   gdb_call_async_signal_handler (sigint_token, immediate_quit);
 }
 
+/* Handle GDB exit upon receiving SIGTERM if target_can_async_p ().  */
+
+static void
+async_sigterm_handler (gdb_client_data arg)
+{
+  quit_force (NULL, stdin == instream);
+}
+
+/* See defs.h.  */
+volatile int sync_quit_force_run;
+
 /* Quit GDB if SIGTERM is received.
    GDB would quit anyway, but this way it will clean up properly.  */
 void
 handle_sigterm (int sig)
 {
   signal (sig, handle_sigterm);
-  quit_force ((char *) 0, stdin == instream);
+
+  if (target_can_async_p ())
+    mark_async_signal_handler (async_sigterm_token);
+  else
+    {
+      sync_quit_force_run = 1;
+      set_quit_flag ();
+    }
 }
 
 /* Do the quit.  All the checks have been done by the caller.  */
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 6ba71ba..e13cc9e 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -4072,8 +4072,15 @@ linux_nat_kill (struct target_ops *ops)
     {
       ptid_t ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
 
+      /* Kill all LWP's before trying to stop them.  In rare cases the
+	 lwp_info state may not match the inferior and
+	 stop_wait_callback could lock up.  */
+      iterate_over_lwps (ptid, kill_callback, NULL);
+
       /* Stop all threads before killing them, since ptrace requires
-	 that the thread is stopped to sucessfully PTRACE_KILL.  */
+	 that the thread is stopped to sucessfully PTRACE_KILL.
+	 kill_callback normally already turned the inferior into a zombie
+	 except for old Linux kernels 2.4.x.  */
       iterate_over_lwps (ptid, stop_callback, NULL);
       /* ... and wait until all of them have reported back that
 	 they're no longer running.  */
diff --git a/gdb/testsuite/gdb.base/gdb-sigterm.c b/gdb/testsuite/gdb.base/gdb-sigterm.c
new file mode 100644
index 0000000..ffa09e4
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gdb-sigterm.c
@@ -0,0 +1,26 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <unistd.h>
+
+int
+main (void)
+{
+  alarm (60);
+
+  for (;;); /* loop-line */
+}
diff --git a/gdb/testsuite/gdb.base/gdb-sigterm.exp b/gdb/testsuite/gdb.base/gdb-sigterm.exp
new file mode 100644
index 0000000..8baeb96
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gdb-sigterm.exp
@@ -0,0 +1,94 @@
+# This testcase is part of GDB, the GNU debugger.
+#
+# Copyright 2013 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+standard_testfile
+
+if { [build_executable ${testfile}.exp ${testfile}] == -1 } {
+    return -1
+}
+
+proc do_test { pass } {
+    global testfile gdb_prompt binfile pf_prefix
+
+    if ![runto_main] {
+	return -1
+    }
+
+    gdb_breakpoint "${testfile}.c:[gdb_get_line_number "loop-line" ${testfile}.c]" \
+		   temporary
+
+    # gdb_continue_to_breakpoint would print a pass message.
+    gdb_test "continue" "Temporary breakpoint .* loop-line .*" ""
+
+    gdb_test_no_output "set range-stepping off" ""
+    gdb_test_no_output "set debug infrun 1" ""
+    gdb_test_no_output "set debug lin-lwp 1" ""
+
+    set test "run a bit #$pass"
+    set abort 1
+    gdb_test_multiple "step" $test {
+	-re "infrun: stepping inside range" {
+	    # Suppress pass $test
+	    verbose -log "$pf_prefix $test"
+	    set abort 0
+	}
+    }
+    if $abort {
+	return
+    }
+
+    set gdb_pid [exp_pid -i [board_info host fileid]]
+    remote_exec host "kill -TERM ${gdb_pid}"
+
+    set test "expect eof #$pass"
+    set abort 1
+    set stepping 0
+    gdb_test_multiple "" $test {
+	eof {
+	    verbose -log "$pf_prefix $test"
+	    set abort 0
+	}
+	-re "infrun: stepping inside range" {
+	    incr stepping
+	    if { $stepping > 200 } {
+		fail "$test (stepping inside range $stepping times)"
+	    } else {
+		exp_continue
+	    }
+	}
+    }
+    if $abort {
+	return
+    }
+}
+
+
+for {set pass 0} {$pass < 50} {incr pass} {
+
+    clean_restart ${testfile}
+    gdb_test_no_output "set target-async off" ""
+    with_test_prefix "sync" {
+        do_test $pass
+    }
+
+    clean_restart ${testfile}
+    gdb_test_no_output "set target-async on" ""
+    with_test_prefix "async" {
+        do_test $pass
+    }
+}
+pass "$pass SIGTERM passes"
diff --git a/gdb/utils.c b/gdb/utils.c
index f5c1339..1a4955c 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -1026,6 +1026,12 @@ print_sys_errmsg (const char *string, int errcode)
 void
 quit (void)
 {
+  if (sync_quit_force_run)
+    {
+      sync_quit_force_run = 0;
+      quit_force (NULL, stdin == instream);
+    }
+
 #ifdef __MSDOS__
   /* No steenking SIGINT will ever be coming our way when the
      program is resumed.  Don't lie.  */