From e76126e8d1fc8e244fbfce03bda4a41a7b7722b1 Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Fri, 11 Jul 2014 11:07:13 +0100 Subject: 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 , func=0x427637 , 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 , action=0x4107a6 ) 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 * 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 * gdb.threads/kill.c: New file. * gdb.threads/kill.exp: New file. --- gdb/gdbserver/linux-low.c | 68 +++++++++++++++++++++++++++++------------------ 1 file changed, 42 insertions(+), 26 deletions(-) (limited to 'gdb/gdbserver/linux-low.c') diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c index 61552f4..215a80c 100644 --- 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); -- cgit v1.1