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USE_SEIZE: fix detaching from stopped processes

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V3: split SEIZE/!SEIZE code paths to reduce confusion.
Extensively comment every possible case.
Verified that all tests/detach* tests work in both SEIZE and !SEIZE
cases.

* strace.c (detach): If PTRACE_SEIZE API is in use, stop the tracee
using PTRACE_INTERRUPT instead of sending it a SIGSTOP.
In a subsequent waitpid loop, correctly wait and suppress SIGSTOP
on detach if PTRACE_INTERRUPT wasn't used, or wait for any ptrace
stop and detach without suppressing signals.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
This commit is contained in:
Denys Vlasenko 2013-06-19 15:31:39 +02:00
parent 0d7c3653c5
commit 69e27ef244
1 changed files with 76 additions and 13 deletions
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89
strace.c
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@ -733,7 +733,7 @@ static int
detach(struct tcb *tcp)
{
int error;
int status, sigstop_expected;
int status, sigstop_expected, interrupt_done;
if (tcp->flags & TCB_BPTSET)
clearbpt(tcp);
@ -750,6 +750,7 @@ detach(struct tcb *tcp)
error = 0;
sigstop_expected = 0;
interrupt_done = 0;
if (tcp->flags & TCB_ATTACHED) {
/*
* We attached but possibly didn't see the expected SIGSTOP.
@ -757,7 +758,7 @@ detach(struct tcb *tcp)
* would be left stopped (process state T).
*/
sigstop_expected = (tcp->flags & TCB_IGNORE_ONE_SIGSTOP);
error = ptrace(PTRACE_DETACH, tcp->pid, (char *) 1, 0);
error = ptrace(PTRACE_DETACH, tcp->pid, 0, 0);
if (error == 0) {
/* On a clear day, you can see forever. */
}
@ -765,20 +766,46 @@ detach(struct tcb *tcp)
/* Shouldn't happen. */
perror_msg("detach: ptrace(PTRACE_DETACH, ...)");
}
else if (my_tkill(tcp->pid, 0) < 0) {
else
/* ESRCH: process is either not stopped or doesn't exist. */
if (my_tkill(tcp->pid, 0) < 0) {
if (errno != ESRCH)
/* Shouldn't happen. */
perror_msg("detach: checking sanity");
}
else if (!sigstop_expected && my_tkill(tcp->pid, SIGSTOP) < 0) {
if (errno != ESRCH)
perror_msg("detach: stopping child");
/* else: process doesn't exist. */
}
else
sigstop_expected = 1;
/* Process is not stopped. */
if (!sigstop_expected) {
/* We need to stop it. */
if (use_seize) {
/*
* With SEIZE, tracee can be in group-stop already.
* In this state sending it another SIGSTOP does nothing.
* Need to use INTERRUPT.
* Testcase: trying to ^C a "strace -p <stopped_process>".
*/
error = ptrace(PTRACE_INTERRUPT, tcp->pid, 0, 0);
if (!error)
interrupt_done = 1;
}
else {
error = my_tkill(tcp->pid, SIGSTOP);
if (!error)
sigstop_expected = 1;
}
if (error && errno != ESRCH) {
if (use_seize)
perror_msg("detach: ptrace(PTRACE_INTERRUPT, ...)");
else
perror_msg("detach: stopping child");
}
}
}
if (sigstop_expected) {
if (sigstop_expected || interrupt_done) {
for (;;) {
int sig;
#ifdef __WALL
if (waitpid(tcp->pid, &status, __WALL) < 0) {
if (errno == ECHILD) /* Already gone. */
@ -810,13 +837,49 @@ detach(struct tcb *tcp)
/* Au revoir, mon ami. */
break;
}
if (WSTOPSIG(status) == SIGSTOP) {
sig = WSTOPSIG(status);
if (debug_flag)
fprintf(stderr, "detach wait: event:%d sig:%d\n",
(unsigned)status >> 16, sig);
if (sigstop_expected && sig == SIGSTOP) {
/* Detach, suppressing SIGSTOP */
ptrace_restart(PTRACE_DETACH, tcp, 0);
break;
}
error = ptrace_restart(PTRACE_CONT, tcp,
WSTOPSIG(status) == syscall_trap_sig ? 0
: WSTOPSIG(status));
if (interrupt_done) {
unsigned event = (unsigned)status >> 16;
if (event == PTRACE_EVENT_STOP /*&& sig == SIGTRAP*/) {
/*
* sig == SIGTRAP: PTRACE_INTERRUPT stop.
* sig == other: process was already stopped
* with this stopping sig (see tests/detach-stopped).
* Looks like re-injecting this sig is not necessary
* in DETACH for the tracee to remain stopped.
*/
sig = 0;
}
/*
* PTRACE_INTERRUPT is not guaranteed to produce
* the above event if other ptrace-stop is pending.
* See tests/detach-sleeping testcase:
* strace got SIGINT while tracee is sleeping.
* We sent PTRACE_INTERRUPT.
* We see syscall exit, not PTRACE_INTERRUPT stop.
* We won't get PTRACE_INTERRUPT stop
* if we would CONT now. Need to DETACH.
*/
if (sig == syscall_trap_sig)
sig = 0;
/* else: not sure in which case we can be here.
* Signal stop? Inject it while detaching.
*/
ptrace_restart(PTRACE_DETACH, tcp, sig);
break;
}
if (sig == syscall_trap_sig)
sig = 0;
/* Can't detach just yet, may need to wait for SIGSTOP */
error = ptrace_restart(PTRACE_CONT, tcp, sig);
if (error < 0)
break;
}