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Re: [PATCH v2] GDBserver crashes when killing a multi-thread process
- From: Yao Qi <qiyaoltc at gmail dot com>
- To: Pedro Alves <palves at redhat dot com>, gdb-patches ml <gdb-patches at sourceware dot org>
- Date: Mon, 13 Jul 2015 17:07:24 +0100
- Subject: Re: [PATCH v2] GDBserver crashes when killing a multi-thread process
- Authentication-results: sourceware.org; auth=none
- References: <510f2362-8d33-4c3c-9a13-5d187f26abdf at SVR-ORW-FEM-04 dot mgc dot mentorg dot com> <53AF87EB dot 60703 at mentor dot com> <53B3CBDB dot 5030207 at redhat dot com> <53BEAE5E dot 7030209 at redhat dot com>
On 10/07/14 16:16, Pedro Alves wrote:
+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);
+}
Hi Pedro,
do you still remember why did you add this assert? It wasn't
mentioned in the mail
https://sourceware.org/ml/gdb-patches/2014-07/msg00206.html
I am looking at a GDBserver internal error on x86_64 when I run
gdb.threads/thread-unwindonsignal.exp with GDBserver,
continue^M
Continuing.^M
warning: Remote failure reply: E.No unwaited-for children left.^M
PC register is not available^M
(gdb) FAIL: gdb.threads/thread-unwindonsignal.exp: continue until exit
Remote debugging from host 127.0.0.1^M
ptrace(regsets_fetch_inferior_registers) PID=30700: No such process^M
ptrace(regsets_fetch_inferior_registers) PID=30700: No such process^M
ptrace(regsets_fetch_inferior_registers) PID=30700: No such process^M
ptrace(regsets_fetch_inferior_registers) PID=30700: No such process^M
monitor exit^M
Killing process(es): 30694^M
(gdb) /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:1106: A
problem internal to GDBserver has been detected.^M
kill_wait_lwp: Assertion `res > 0' failed.
After your patch https://sourceware.org/ml/gdb-patches/2015-03/msg00597.html
GDBserver starts to swallows errors if the LWP is gone. Then, when
GDBservers kills non-exist LWP, the assert will be triggered.
Why don't we implement kill_wait_lwp like its counterpart in GDB
linux-nat.c:kill_wait_callback? we can loop and assert like this
patch below, (note that this patch fixes the internal error, and
the FAIL is still there).
--
Yao (éå)
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 7bb9f7f..07d051a 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -1101,9 +1101,9 @@ kill_wait_lwp (struct lwp_info *lwp)
res = my_waitpid (lwpid, &wstat, 0);
if (res == -1 && errno == ECHILD)
res = my_waitpid (lwpid, &wstat, __WCLONE);
- } while (res > 0 && WIFSTOPPED (wstat));
+ } while (res == lwpid);
- gdb_assert (res > 0);
+ gdb_assert (res == -1 && errno == ECHILD);
}
/* Callback for `find_inferior'. Kills an lwp of a given process,