GDBserver crashes when killing a multi-thread process

Here's an example, with the new test: gdbserver :9999 gdb.threads/kill gdb gdb.threads/kill (gdb) b 52 Breakpoint 1 at 0x4007f4: file kill.c, line 52. Continuing. Breakpoint 1, main () at kill.c:52 52 return 0; /* set break here */ (gdb) k Kill the program being debugged? (y or n) y gdbserver :9999 gdb.threads/kill Process gdb.base/watch_thread_num created; pid = 9719 Listening on port 1234 Remote debugging from host 127.0.0.1 Killing all inferiors Segmentation fault (core dumped) Backtrace: (gdb) bt #0 0x00000000004068a0 in find_inferior (list=0x66b060 <all_threads>, func=0x427637 <kill_one_lwp_callback>, arg=0x7fffffffd3fc) at src/gdb/gdbserver/inferiors.c:199 #1 0x00000000004277b6 in linux_kill (pid=15708) at src/gdb/gdbserver/linux-low.c:966 #2 0x000000000041354d in kill_inferior (pid=15708) at src/gdb/gdbserver/target.c:163 #3 0x00000000004107e9 in kill_inferior_callback (entry=0x6704f0) at src/gdb/gdbserver/server.c:2934 #4 0x0000000000406522 in for_each_inferior (list=0x66b050 <all_processes>, action=0x4107a6 <kill_inferior_callback>) at src/gdb/gdbserver/inferiors.c:57 #5 0x0000000000412377 in process_serial_event () at src/gdb/gdbserver/server.c:3767 #6 0x000000000041267c in handle_serial_event (err=0, client_data=0x0) at src/gdb/gdbserver/server.c:3880 #7 0x00000000004189ff in handle_file_event (event_file_desc=4) at src/gdb/gdbserver/event-loop.c:434 #8 0x00000000004181c6 in process_event () at src/gdb/gdbserver/event-loop.c:189 #9 0x0000000000418f45 in start_event_loop () at src/gdb/gdbserver/event-loop.c:552 #10 0x0000000000411272 in main (argc=3, argv=0x7fffffffd8d8) at src/gdb/gdbserver/server.c:3283 The problem is that linux_wait_for_event deletes lwps that have exited (even those not passed in as lwps of interest), while the lwp/thread list is being walked on with find_inferior. find_inferior can handle the current iterated inferior being deleted, but not others. When killing lwps, we don't really care about any of the pending status handling of linux_wait_for_event. We can just waitpid the lwps directly, which is also what GDB does (see linux-nat.c:kill_wait_callback). This way the lwps are not deleted while we're walking the list. They'll be deleted by linux_mourn afterwards. This crash triggers several times when running the testsuite against GDBserver with the native-gdbserver board (target remote), but as GDB can't distinguish between GDBserver crashing and "kill" being sucessful, as in both cases the connection is closed (the 'k' packet doesn't require a reply), and the inferior is gone, that results in no FAIL. The patch adds a generic test that catches the issue with extended-remote mode (and works fine with native testing too). Here's how it fails with the native-extended-gdbserver board without the fix: (gdb) info threads Id Target Id Frame 6 Thread 15367.15374 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81 5 Thread 15367.15373 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81 4 Thread 15367.15372 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81 3 Thread 15367.15371 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81 2 Thread 15367.15370 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81 * 1 Thread 15367.15367 main () at .../gdb.threads/kill.c:52 (gdb) kill Kill the program being debugged? (y or n) y Remote connection closed ^^^^^^^^^^^^^^^^^^^^^^^^ (gdb) FAIL: gdb.threads/kill.exp: kill Extended remote should remain connected after the kill. gdb/gdbserver/ 2014-07-11 Pedro Alves <[email protected]> * linux-low.c (kill_wait_lwp): New function, based on kill_one_lwp_callback, but use my_waitpid directly. (kill_one_lwp_callback, linux_kill): Use it. gdb/testsuite/ 2014-07-11 Pedro Alves <[email protected]> * gdb.threads/kill.c: New file. * gdb.threads/kill.exp: New file.
ibuclaw · Jul 11, 2014 · e76126e · e76126e
1 parent b9c1d48
commit e76126e
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diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,9 @@
+2014-07-11  Pedro Alves  <[email protected]>
+
+	* linux-low.c (kill_wait_lwp): New function, based on
+	kill_one_lwp_callback, but use my_waitpid directly.
+	(kill_one_lwp_callback, linux_kill): Use it.
+
 2014-06-23  Pedro Alves  <[email protected]>
 
 	* linux-x86-low.c (x86_linux_prepare_to_resume): Clear DR_CONTROL

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
@@ -909,6 +909,46 @@ linux_kill_one_lwp (struct lwp_info *lwp)
 		  errno ? strerror (errno) : "OK");
 }
 
+/* Kill LWP and wait for it to die.  */
+
+static void
+kill_wait_lwp (struct lwp_info *lwp)
+{
+  struct thread_info *thr = get_lwp_thread (lwp);
+  int pid = ptid_get_pid (ptid_of (thr));
+  int lwpid = ptid_get_lwp (ptid_of (thr));
+  int wstat;
+  int res;
+
+  if (debug_threads)
+    debug_printf ("kwl: killing lwp %d, for pid: %d\n", lwpid, pid);
+
+  do
+    {
+      linux_kill_one_lwp (lwp);
+
+      /* Make sure it died.  Notes:
+
+	 - The loop is most likely unnecessary.
+
+	 - We don't use linux_wait_for_event as that could delete lwps
+	   while we're iterating over them.  We're not interested in
+	   any pending status at this point, only in making sure all
+	   wait status on the kernel side are collected until the
+	   process is reaped.
+
+	 - We don't use __WALL here as the __WALL emulation relies on
+	   SIGCHLD, and killing a stopped process doesn't generate
+	   one, nor an exit status.
+      */
+      res = my_waitpid (lwpid, &wstat, 0);
+      if (res == -1 && errno == ECHILD)
+	res = my_waitpid (lwpid, &wstat, __WCLONE);
+    } while (res > 0 && WIFSTOPPED (wstat));
+
+  gdb_assert (res > 0);
+}
+
 /* Callback for `find_inferior'.  Kills an lwp of a given process,
    except the leader.  */
 
@@ -917,7 +957,6 @@ kill_one_lwp_callback (struct inferior_list_entry *entry, void *args)
 {
   struct thread_info *thread = (struct thread_info *) entry;
   struct lwp_info *lwp = get_thread_lwp (thread);
-  int wstat;
   int pid = * (int *) args;
 
   if (ptid_get_pid (entry->id) != pid)
@@ -936,14 +975,7 @@ kill_one_lwp_callback (struct inferior_list_entry *entry, void *args)
       return 0;
     }
 
-  do
-    {
-      linux_kill_one_lwp (lwp);
-
-      /* Make sure it died.  The loop is most likely unnecessary.  */
-      pid = linux_wait_for_event (thread->entry.id, &wstat, __WALL);
-    } while (pid > 0 && WIFSTOPPED (wstat));
-
+  kill_wait_lwp (lwp);
   return 0;
 }
 
@@ -952,8 +984,6 @@ linux_kill (int pid)
 {
   struct process_info *process;
   struct lwp_info *lwp;
-  int wstat;
-  int lwpid;
 
   process = find_process_pid (pid);
   if (process == NULL)
@@ -976,21 +1006,7 @@ linux_kill (int pid)
 		      pid);
     }
   else
-    {
-      struct thread_info *thr = get_lwp_thread (lwp);
-
-      if (debug_threads)
-	debug_printf ("lk_1: killing lwp %ld, for pid: %d\n",
-		      lwpid_of (thr), pid);
-
-      do
-	{
-	  linux_kill_one_lwp (lwp);
-
-	  /* Make sure it died.  The loop is most likely unnecessary.  */
-	  lwpid = linux_wait_for_event (thr->entry.id, &wstat, __WALL);
-	} while (lwpid > 0 && WIFSTOPPED (wstat));
-    }
+    kill_wait_lwp (lwp);
 
   the_target->mourn (process);
 

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2014-07-11  Pedro Alves  <[email protected]>
+
+	* gdb.threads/kill.c: New file.
+	* gdb.threads/kill.exp: New file.
+
 2014-07-10  Yao Qi  <[email protected]>
 
 	* gdb.trace/tfile.c (write_basic_trace_file)

diff --git a/gdb/testsuite/gdb.threads/kill.c b/gdb/testsuite/gdb.threads/kill.c
@@ -0,0 +1,64 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014 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/>.  */
+
+#ifdef USE_THREADS
+
+#include <unistd.h>
+#include <pthread.h>
+
+#define NUM 5
+
+pthread_barrier_t barrier;
+
+void *
+thread_function (void *arg)
+{
+  volatile unsigned int counter = 1;
+
+  pthread_barrier_wait (&barrier);
+
+  while (counter > 0)
+    {
+      counter++;
+      usleep (1);
+    }
+
+  pthread_exit (NULL);
+}
+
+#endif /* USE_THREADS */
+
+void
+setup (void)
+{
+#ifdef USE_THREADS
+  pthread_t threads[NUM];
+  int i;
+
+  pthread_barrier_init (&barrier, NULL, NUM + 1);
+  for (i = 0; i < NUM; i++)
+    pthread_create (&threads[i], NULL, thread_function, NULL);
+  pthread_barrier_wait (&barrier);
+#endif /* USE_THREADS */
+}
+
+int
+main (void)
+{
+  setup ();
+  return 0; /* set break here */
+}
diff --git a/gdb/testsuite/gdb.threads/kill.exp b/gdb/testsuite/gdb.threads/kill.exp
@@ -0,0 +1,77 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2014 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
+
+# Run the test proper.  THREADED indicates whether to build a threaded
+# program and spawn several threads before trying to kill the program.
+
+proc test {threaded} {
+    global testfile srcfile
+
+    with_test_prefix [expr ($threaded)?"threaded":"non-threaded"] {
+
+	set options {debug}
+	if {$threaded} {
+	    lappend options "pthreads"
+	    lappend options "additional_flags=-DUSE_THREADS"
+	    set prog ${testfile}_threads
+	} else {
+	    set prog ${testfile}_nothreads
+	}
+
+	if {[prepare_for_testing "failed to prepare" $prog $srcfile $options] == -1} {
+	    return -1
+	}
+
+	if { ![runto main] } then {
+	    fail "run to main"
+	    return
+	}
+
+	set linenum [gdb_get_line_number "set break here"]
+	gdb_breakpoint "$srcfile:$linenum"
+	gdb_continue_to_breakpoint "break here" ".*break here.*"
+
+	if {$threaded} {
+	    gdb_test "info threads" "6.*5.*4.*3.*2.*1.*" "all threads started"
+	}
+
+	# This kills and ensures no output other than the prompt comes out,
+	# like:
+	#
+	#  (gdb) kill
+	#  Kill the program being debugged? (y or n) y
+	#  (gdb)
+	#
+	# If we instead saw more output, like e.g., with an extended-remote
+	# connection:
+	#
+	#  (gdb) kill
+	#  Kill the program being debugged? (y or n) y
+	#  Remote connection closed
+	#  (gdb)
+	#
+	# the above would mean that the remote end crashed.
+
+	gdb_test "kill" "^y" "kill program" "Kill the program being debugged\\? \\(y or n\\) $" "y"
+    }
+}
+
+foreach threaded {true false} {
+    test $threaded
+}