[PING][PATCH][gdb] Fix hang after ext sigkill

[Tom de Vries <tdevries@suse.de>]

On 24-02-2020 21:14, Tom de Vries wrote:
> Hi,
> 
> Consider the test-case from this patch, compiled with pthread support:
> ...
> $ gcc src/gdb/testsuite/gdb.threads/hang-after-ext-sigkill.c -lpthread
> ...
> 
> After running, the program sleeps:
> ...
> $ gdb a.out
> Reading symbols from a.out...
> (gdb) r
> Starting program: /data/gdb_versions/devel/a.out
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib64/libthread_db.so.1".
> [New Thread 0x7ffff77fe700 (LWP 22604)]
> ...
> 
> Until we interrupt it with a control-C:
> ...
> ^C
> Thread 1 "a.out" received signal SIGINT, Interrupt.
> 0x00007ffff78c50f0 in nanosleep () from /lib64/libc.so.6
> (gdb)
> ...
> 
> If we then kill the inferior using an external SIGKILL:
> ...
> (gdb) shell killall -s SIGKILL a.out
> ...
> and subsequently continue:
> ...
> (gdb) c
> Continuing.
> Couldn't get registers: No such process.
> Couldn't get registers: No such process.
> (gdb) Couldn't get registers: No such process.
> (gdb) Couldn't get registers: No such process.
> (gdb) Couldn't get registers: No such process.
> <repeat>
> ...
> gdb hangs which repeating the same warning.  Typing control-C no longer helps,
> and we have to kill gdb using kill.
> 
> This is a regression since commit 873657b9e8 "Preserve selected thread in
> all-stop w/ background execution".  The commit adds a
> scoped_restore_current_thread typed variable restore_thread to
> fetch_inferior_event, and the hang is caused by the constructor throwing an
> exception.
> 
> Fix this by catching the exception in the constructor.
> 
> Build and reg-tested on x86_64-linux.
> 
> OK for trunk?
> 

Ping.

Thanks,
- Tom

> [gdb] Fix hang after ext sigkill
> 
> gdb/ChangeLog:
> 
> 2020-02-24  Tom de Vries  <tdevries@suse.de>
> 
> 	PR gdb/25471
> 	* thread.c
> 	(scoped_restore_current_thread::scoped_restore_current_thread): Catch
> 	exception in get_frame_id.
> 	(scoped_restore_current_thread::~scoped_restore_current_thread):
> 	Handle lack of inferior.
> 
> gdb/testsuite/ChangeLog:
> 
> 2020-02-24  Tom de Vries  <tdevries@suse.de>
> 
> 	PR gdb/25471
> 	* gdb.threads/hang-after-ext-sigkill.c: New test.
> 	* gdb.threads/hang-after-ext-sigkill.exp: New file.
> 	* lib/gdb.exp (runto): Handle "Temporary breakpoint" string.
> 
> ---
>  gdb/testsuite/gdb.threads/hang-after-ext-sigkill.c | 40 ++++++++++++
>  .../gdb.threads/hang-after-ext-sigkill.exp         | 73 ++++++++++++++++++++++
>  gdb/testsuite/lib/gdb.exp                          |  2 +-
>  gdb/thread.c                                       | 14 ++++-
>  4 files changed, 127 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/testsuite/gdb.threads/hang-after-ext-sigkill.c b/gdb/testsuite/gdb.threads/hang-after-ext-sigkill.c
> new file mode 100644
> index 0000000000..bfce6c3085
> --- /dev/null
> +++ b/gdb/testsuite/gdb.threads/hang-after-ext-sigkill.c
> @@ -0,0 +1,40 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +
> +   Copyright 2020 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 <pthread.h>
> +#include <unistd.h>
> +
> +static void *
> +fun (void *dummy)
> +{
> +  while (1)
> +    sleep (1);
> +
> +  return NULL;
> +}
> +
> +int
> +main (void)
> +{
> +  pthread_t thread;
> +  pthread_create (&thread, NULL, fun, NULL);
> +
> +  while (1)
> +    sleep (1);
> +
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.threads/hang-after-ext-sigkill.exp b/gdb/testsuite/gdb.threads/hang-after-ext-sigkill.exp
> new file mode 100644
> index 0000000000..3702eb8c13
> --- /dev/null
> +++ b/gdb/testsuite/gdb.threads/hang-after-ext-sigkill.exp
> @@ -0,0 +1,73 @@
> +# Copyright (C) 2020 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 {[prepare_for_testing "failed to prepare" $testfile $srcfile \
> +	 {pthreads}] == -1} {
> +    return -1
> +}
> +
> +set res [runto main no-message temporary]
> +if { $res != 1 } {
> +    return -1
> +}
> +
> +set pid -1
> +gdb_test_multiple "info inferior 1" "get inferior pid" {
> +    -re -wrap "process (\[0-9\]*).*" {
> +       set pid $expect_out(1,string)
> +       pass $gdb_test_name
> +    }
> +}
> +if { $pid == -1 } {
> +    return -1
> +}
> +
> +gdb_test_multiple "continue" "" {
> +    -re "Continuing" {
> +	pass $gdb_test_name
> +    }
> +}
> +
> +send_gdb "\003"
> +
> +gdb_test_multiple "" "get sigint" {
> +    -re -wrap "Thread \[0-9\]+ .* received signal SIGINT, Interrupt\..*" {
> +       pass $gdb_test_name
> +   }
> +}
> +
> +gdb_test_no_output "shell kill -s SIGKILL $pid" "shell kill -s SIGKILL pid"
> +
> +# Expect the signal to arrive, and the program to terminate.
> +# Ideally at the first continue, currently though at the second.
> +set killed_msg "Program terminated with signal SIGKILL, Killed\."
> +set no_longer_exists_msg "The program no longer exists\."
> +set not_being_run_msg "The program is not being run\."
> +set msg [join [list $killed_msg $no_longer_exists_msg $not_being_run_msg] \
> +	     ".*"]
> +
> +# Don't expect '$gdb_prompt $', there still may be output after the prompt,
> +# f.i.:
> +# ...
> +# (gdb) [Thread 0x7ffff74c6700 (LWP 19277) exited]^M
> +# ...
> +gdb_test_multiple "continue" "" {
> +    -re ".*\r\n$gdb_prompt " {
> +	gdb_test "continue" $msg $gdb_test_name
> +    }
> +}
> +
> diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
> index 81518b9646..745694df2d 100644
> --- a/gdb/testsuite/lib/gdb.exp
> +++ b/gdb/testsuite/lib/gdb.exp
> @@ -571,7 +571,7 @@ proc runto { function args } {
>  	    }
>  	    return 1
>  	}
> -	-re "Breakpoint \[0-9\]*, \[0-9xa-f\]* in .*$gdb_prompt $" { 
> +	-re "\[Bb\]reakpoint \[0-9\]*, \[0-9xa-f\]* in .*$gdb_prompt $" {
>  	    if { $print_pass } {
>  		pass $test_name
>  	    }
> diff --git a/gdb/thread.c b/gdb/thread.c
> index 54b59e2244..9876ca3c76 100644
> --- a/gdb/thread.c
> +++ b/gdb/thread.c
> @@ -1444,6 +1444,8 @@ scoped_restore_current_thread::restore ()
>  
>  scoped_restore_current_thread::~scoped_restore_current_thread ()
>  {
> +  if (m_inf == NULL)
> +    return;
>    if (!m_dont_restore)
>      {
>        try
> @@ -1488,7 +1490,17 @@ scoped_restore_current_thread::scoped_restore_current_thread ()
>        else
>  	frame = NULL;
>  
> -      m_selected_frame_id = get_frame_id (frame);
> +      try
> +       {
> +	 m_selected_frame_id = get_frame_id (frame);
> +       }
> +      catch (const gdb_exception &ex)
> +       {
> +	 m_inf = NULL;
> +	 m_selected_frame_id = null_frame_id;
> +	 m_selected_frame_level = -1;
> +	 return;
> +       }
>        m_selected_frame_level = frame_relative_level (frame);
>  
>        tp->incref ();
>