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[patchv3] Fix SIGTERM signal safety (PR gdb/15358)
- From: Jan Kratochvil <jan dot kratochvil at redhat dot com>
- To: Doug Evans <dje at google dot com>
- Cc: gdb-patches at sourceware dot org
- Date: Sun, 16 Mar 2014 14:53:34 +0100
- Subject: [patchv3] Fix SIGTERM signal safety (PR gdb/15358)
- Authentication-results: sourceware.org; auth=none
- References: <20140314183709 dot GA28050 at host2 dot jankratochvil dot net> <20140314184535 dot GA30853 at host2 dot jankratochvil dot net> <21284 dot 44419 dot 745786 dot 47756 at ruffy dot mtv dot corp dot google dot com>
On Sat, 15 Mar 2014 20:44:03 +0100, Doug Evans wrote:
> A high level comment is that I guess this patch means it's
> now more important to fix the spots of gdb where QUITs aren't
> called for long times
I do not see it so much related. The problem is if GDB locks up and never
terminates like in this PR.
> Jan Kratochvil writes:
> > + async_sigterm_token =
> > + create_async_signal_handler (async_sigterm_handler, NULL);
> > }
>
> I realize SIGTERM isn't handled exactly like SIGINT, but IWBN
> to keep all the SIGTERM bits together in this function.
> How about moving the above snippet to after this:
I agree, done.
> btw, the rule has been effectively changed to require = being
> put on the next line.
> While I certainly wouldn't ask for whitespace change in this patch,
> [IOW I'm not asking for the existing code to be fixed]
This is wrong. If there should be some rule benefiting some unification of
the code base then the codebase has to be reformatted to such rule first.
> I'm curious what the rule is for handling this here.
> For the patch at hand, should it be written as this:
>
> async_sigterm_token =
> create_async_signal_handler (async_sigterm_handler, NULL);
>
> or this:
>
> async_sigterm_token
> = create_async_signal_handler (async_sigterm_handler, NULL);
>
> ?
> I honestly don't know.
This is one of the problems of GDB.
I have changed my patch but I do not know according to which rule and it no
longer matches the existing code around.
[...]
> > void
> > handle_sigterm (int sig)
> > {
> > signal (sig, handle_sigterm);
> > - quit_force ((char *) 0, stdin == instream);
>
> I think we need a comment here explaining *why* we can't
> just call quit_force here.
Added there:
/* Call quit_force in a signal safe way.
quit_force itself is not signal safe. */
> > +
> > + if (target_can_async_p ())
> > + mark_async_signal_handler (async_sigterm_token);
> > + else
> > + {
> > + sync_quit_force_run = 1;
> > + set_quit_flag ();
> > + }
> > }
> > --- a/gdb/linux-nat.c
> > +++ b/gdb/linux-nat.c
> > @@ -3777,8 +3777,15 @@ 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. */
>
> This part feels sufficiently outside the scope of this patch
> that IWBN if this were a separate patch.
OK, moved this one to a different patch.
[...]
> > +for {set pass 0} {$pass < 50} {incr pass} {
>
> How come 50 passes?
> At the least a comment is required explaining why.
Added:
# Testcase was FAILing approx. on 10th pass with unpatched GDB.
# 50 runs should be approx. a safe number to be sure it is fixed now.
Thanks,
Jan
gdb/
2014-03-16 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.
* utils.c (quit): Call quit_force if SYNC_QUIT_FORCE_RUN.
gdb/testsuite/
2014-03-16 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 480133d..47da43a 100644
--- a/gdb/defs.h
+++ b/gdb/defs.h
@@ -171,6 +171,9 @@ 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);
@@ -183,7 +186,7 @@ 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 fbe89bd..c353f48 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
@@ -733,6 +735,8 @@ async_init_signals (void)
sigint_token =
create_async_signal_handler (async_request_quit, NULL);
signal (SIGTERM, handle_sigterm);
+ async_sigterm_token
+ = create_async_signal_handler (async_sigterm_handler, NULL);
/* If SIGTRAP was set to SIG_IGN, then the SIG_IGN will get passed
to the inferior and breakpoints will be ignored. */
@@ -769,7 +773,6 @@ async_init_signals (void)
sigtstp_token =
create_async_signal_handler (async_stop_sig, NULL);
#endif
-
}
/* Tell the event loop what to do if SIGINT is received.
@@ -797,13 +800,33 @@ 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);
+
+ /* Call quit_force in a signal safe way.
+ quit_force itself is not signal safe. */
+ 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/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..b57680d
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gdb-sigterm.exp
@@ -0,0 +1,96 @@
+# 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 $abort {
+ return
+ }
+}
+
+# Testcase was FAILing approx. on 10th pass with unpatched GDB.
+# 50 runs should be approx. a safe number to be sure it is fixed now.
+
+for {set pass 0} {$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 9d068c5..364470c 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -999,6 +999,12 @@ 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. */