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Remove TCB_SUSPENDED constant and related code.

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Since we no longer suspend waitpid'ing tracees, we have only one case when
we suspend tracee: when we pick up a new tracee created by clone/fork/vfork.

Background: on some other OSes, attach to child is done this way:
get fork's result (pid), loop ptrace(PTRACE_ATTACH) until you hook up
new process/thread. This is ugly and not safe, but what matters for us
is that it doesn't require suspending. Suspending is required
on Linux only, because on Linux attach to child is done differently.

On Linux, we use two methods of catching new tracee:
adding CLONE_THREAD bit to syscall (if needed, we change
[v]fork into clone before that), or using ptrace options.
In both cases, it may be so that new tracee appears before one which
created it returns from syscall. In this case, current code
suspends new tracee until its creator returns. Only then
strace can determine who is its parent (it needs child's pid for this,
which is visible in parent's [v]fork/clone result).
This is inherently racy. For example, what if SIGKILL kills
creator after it succeeded creating child, but before it returns?
Looks like we will have child suspended forever.

But after previous commit, we DO NOT NEED parent<->child link for anything.
Therefore we do not need suspending too. Bingo!

This patch removes suspending code. Now new tracees will be continued
right away. Next patch will remove tcp->parent member.

* defs.h: Remove TCB_SUSPENDED constant
* process.c (handle_new_child): Delete this function.
  (internal_fork): Do not call handle_new_child on syscall exit.
* strace.c (handle_ptrace_event): Delete this function.
  (trace): Do not suspend new child; remove all handling
  of now impossible TCB_SUSPENDED condition.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
This commit is contained in:
Denys Vlasenko 2011-08-17 11:30:56 +02:00
parent 19cdada5b4
commit 833fb13cef
3 changed files with 9 additions and 154 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
defs.h
View File

@ -411,7 +411,6 @@ struct tcb {
#define TCB_INUSE 00002 /* This table entry is in use */
#define TCB_INSYSCALL 00004 /* A system call is in progress */
#define TCB_ATTACHED 00010 /* Process is not our own child */
#define TCB_SUSPENDED 00040 /* Process can not be allowed to resume just now */
#define TCB_BPTSET 00100 /* "Breakpoint" set after fork(2) */
#define TCB_SIGTRAPPED 00200 /* Process wanted to block SIGTRAP */
#define TCB_REPRINT 01000 /* We should reprint this syscall on exit */

110
process.c
View File

@ -762,94 +762,6 @@ change_syscall(struct tcb *tcp, int new)
}
#ifdef LINUX
int
handle_new_child(struct tcb *tcp, int pid, int bpt)
{
struct tcb *tcpchild;
tcpchild = pid2tcb(pid);
if (tcpchild != NULL) {
/* The child already reported its startup trap
before the parent reported its syscall return. */
if ((tcpchild->flags
& (TCB_STARTUP|TCB_ATTACHED|TCB_SUSPENDED))
!= (TCB_STARTUP|TCB_ATTACHED|TCB_SUSPENDED))
fprintf(stderr, "\
[preattached child %d of %d in weird state!]\n",
pid, tcp->pid);
}
else {
tcpchild = alloctcb(pid);
}
tcpchild->flags |= TCB_ATTACHED;
if (bpt) {
clearbpt(tcp);
/* Child has BPT too, must be removed on first occasion. */
tcpchild->flags |= TCB_BPTSET;
tcpchild->baddr = tcp->baddr;
memcpy(tcpchild->inst, tcp->inst,
sizeof tcpchild->inst);
}
tcpchild->parent = tcp;
if (tcpchild->flags & TCB_SUSPENDED) {
/* The child was born suspended, due to our having
forced CLONE_PTRACE. */
if (bpt)
clearbpt(tcpchild);
tcpchild->flags &= ~(TCB_SUSPENDED|TCB_STARTUP);
if (ptrace_restart(PTRACE_SYSCALL, tcpchild, 0) < 0)
return -1;
if (!qflag)
fprintf(stderr, "\
Process %u resumed (parent %d ready)\n",
pid, tcp->pid);
}
else {
if (!qflag)
fprintf(stderr, "Process %d attached\n", pid);
}
#ifdef TCB_CLONE_THREAD
if (sysent[tcp->scno].sys_func == sys_clone) {
/*
* Save the flags used in this call,
* in case we point TCP to our parent below.
*/
int call_flags = tcp->u_arg[ARG_FLAGS];
if ((tcp->flags & TCB_CLONE_THREAD) &&
tcp->parent != NULL) {
/* The parent in this clone is itself a
thread belonging to another process.
There is no meaning to the parentage
relationship of the new child with the
thread, only with the process. We
associate the new thread with our
parent. Since this is done for every
new thread, there will never be a
TCB_CLONE_THREAD process that has
children. */
tcp = tcp->parent;
tcpchild->parent = tcp;
}
if (call_flags & CLONE_THREAD) {
tcpchild->flags |= TCB_CLONE_THREAD;
}
if ((call_flags & CLONE_PARENT) &&
!(call_flags & CLONE_THREAD)) {
tcpchild->parent = NULL;
if (tcp->parent != NULL) {
tcp = tcp->parent;
tcpchild->parent = tcp;
}
}
}
#endif /* TCB_CLONE_THREAD */
return 0;
}
int
internal_fork(struct tcb *tcp)
@ -864,29 +776,17 @@ internal_fork(struct tcb *tcp)
if (entering(tcp)) {
/*
* In occasion of using PTRACE_O_TRACECLONE, we won't see the
* new child if clone is called with flag CLONE_UNTRACED, so
* we keep the same logic with that option and don't trace it.
* We won't see the new child if clone is called with
* CLONE_UNTRACED, so we keep the same logic with that option
* and don't trace it.
*/
if ((sysent[tcp->scno].sys_func == sys_clone) &&
(tcp->u_arg[ARG_FLAGS] & CLONE_UNTRACED))
return 0;
setbpt(tcp);
} else {
int pid;
int bpt;
bpt = tcp->flags & TCB_BPTSET;
if (syserror(tcp)) {
if (bpt)
clearbpt(tcp);
return 0;
}
pid = tcp->u_rval;
return handle_new_child(tcp, pid, bpt);
if (tcp->flags & TCB_BPTSET)
clearbpt(tcp);
}
return 0;
}

52
strace.c
View File

@ -2216,32 +2216,6 @@ trace(void)
#else /* !USE_PROCFS */
#ifdef LINUX
static int
handle_ptrace_event(int status, struct tcb *tcp)
{
if (status >> 16 == PTRACE_EVENT_VFORK ||
status >> 16 == PTRACE_EVENT_CLONE ||
status >> 16 == PTRACE_EVENT_FORK) {
long childpid;
if (do_ptrace(PTRACE_GETEVENTMSG, tcp, NULL, &childpid) < 0) {
if (errno != ESRCH) {
error_msg_and_die("Cannot get new child's pid");
}
return -1;
}
return handle_new_child(tcp, childpid, 0);
}
if (status >> 16 == PTRACE_EVENT_EXEC) {
return 0;
}
/* Some PTRACE_EVENT_foo we didn't ask for?! */
error_msg("Unexpected status %x on pid %d", status, tcp->pid);
return 1;
}
#endif
static int
trace()
{
@ -2369,10 +2343,9 @@ trace()
child so that we know how to do clearbpt
in the child. */
tcp = alloctcb(pid);
tcp->flags |= TCB_ATTACHED | TCB_SUSPENDED;
tcp->flags |= TCB_ATTACHED;
if (!qflag)
fprintf(stderr, "\
Process %d attached (waiting for parent)\n",
fprintf(stderr, "Process %d attached\n",
pid);
}
else
@ -2395,17 +2368,6 @@ Process %d attached (waiting for parent)\n",
}
#endif
if (tcp->flags & TCB_SUSPENDED) {
/*
* Apparently, doing any ptrace() call on a stopped
* process, provokes the kernel to report the process
* status again on a subsequent wait(), even if the
* process has not been actually restarted.
* Since we have inspected the arguments of suspended
* processes we end up here testing for this case.
*/
continue;
}
if (WIFSIGNALED(status)) {
if (pid == strace_child)
exit_code = 0x100 | WTERMSIG(status);
@ -2449,8 +2411,8 @@ Process %d attached (waiting for parent)\n",
}
if (status >> 16) {
if (handle_ptrace_event(status, tcp) != 1)
goto tracing;
/* Ptrace event (we ignore all of them for now) */
goto tracing;
}
/*
@ -2548,7 +2510,6 @@ Process %d attached (waiting for parent)\n",
cleanup();
return -1;
}
tcp->flags &= ~TCB_SUSPENDED;
continue;
}
/* we handled the STATUS, we are permitted to interrupt now. */
@ -2579,11 +2540,6 @@ Process %d attached (waiting for parent)\n",
}
continue;
}
if (tcp->flags & TCB_SUSPENDED) {
if (!qflag)
fprintf(stderr, "Process %u suspended\n", pid);
continue;
}
tracing:
/* Remember current print column before continuing. */
tcp->curcol = curcol;