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[140.211.15.137]) by smtp.gmail.com with ESMTPSA id ky17sm12791576pab.31.2015.07.13.09.07.30 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 Jul 2015 09:07:31 -0700 (PDT) Message-ID: <55A3E23C.8020101@gmail.com> Date: Mon, 13 Jul 2015 17:07:24 +0100 From: Yao Qi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Pedro Alves , gdb-patches ml Subject: Re: [PATCH v2] GDBserver crashes when killing a multi-thread process References: <510f2362-8d33-4c3c-9a13-5d187f26abdf@SVR-ORW-FEM-04.mgc.mentorg.com> <53AF87EB.60703@mentor.com> <53B3CBDB.5030207@redhat.com> <53BEAE5E.7030209@redhat.com> In-Reply-To: <53BEAE5E.7030209@redhat.com> X-IsSubscribed: yes 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). 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,