Do not detach from tracee which experienced ptrace error.

Before this patch, if a thread got nuked by exit in another thread
and we happened to poke it at the same time, we print "????(" thingy
and detach the thread. Since we removed "detach before death" logic,
this no longer matches the behavior of other threads.
Before patch:
[pid  1780] exit_group(1)               = ?
[pid  1778] ????( <unfinished ...>
Process 1778 detached
[pid  5860] +++ exited with 1 +++
After:
[pid 17765] exit_group(1)               = ?
[pid 21680] ????( <unfinished ...>
[pid 17791] +++ exited with 1 +++
[pid 21680] +++ exited with 1 +++

* strace (trace): Do not detach from tracee which experienced ptrace error.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

diff --git a/strace.c b/strace.c
index 463ce1ffedd1be40f26896df14121423c34a1026..910a11c96ef024ee14bfba6c5e9de3235e02487e 100644 (file)
--- a/strace.c
+++ b/strace.c
@@ -2596,9 +2596,7 @@ trace()
                        /* ptrace() failed in trace_syscall() with ESRCH.
                         * Likely a result of process disappearing mid-flight.
                         * Observed case: exit_group() terminating
-                        * all processes in thread group. In this case, threads
-                        * "disappear" in an unpredictable moment without any
-                        * notification to strace via wait().
+                        * all processes in thread group.
                         */
                        if (tcp->flags & TCB_ATTACHED) {
                                if (tcp_last) {
@@ -2609,11 +2607,16 @@ trace()
                                        tprints(" <unfinished ...>");
                                        printtrailer();
                                }
-                               detach(tcp);
+                               /* We assume that ptrace error was caused by process death.
+                                * We used to detach(tcp) here, but since we no longer
+                                * implement "detach before death" policy/hack,
+                                * we can let this process to report its death to us
+                                * normally, via WIFEXITED or WIFSIGNALED wait status.
+                                */
                        } else {
-                               ptrace(PTRACE_KILL,
-                                       tcp->pid, (char *) 1, SIGTERM);
-                               droptcb(tcp);
+                               /* It's our real child (and we also trace it) */
+                               /* my_tkill(pid, SIGKILL); - why? */
+                               /* droptcb(tcp); - why? */
                        }
                        continue;
                }