svn commit: r335820 - in stable/11/sys: kern sys
Konstantin Belousov
kib at FreeBSD.org
Sat Jun 30 15:07:47 UTC 2018
Author: kib
Date: Sat Jun 30 15:07:44 2018
New Revision: 335820
URL: https://svnweb.freebsd.org/changeset/base/335820
Log:
MFC r335504:
fork: avoid endless wait with PTRACE_FORK and RFSTOPPED.
Modified:
stable/11/sys/kern/kern_fork.c
stable/11/sys/kern/kern_proc.c
stable/11/sys/kern/kern_sig.c
stable/11/sys/sys/proc.h
Directory Properties:
stable/11/ (props changed)
Modified: stable/11/sys/kern/kern_fork.c
==============================================================================
--- stable/11/sys/kern/kern_fork.c Sat Jun 30 15:03:22 2018 (r335819)
+++ stable/11/sys/kern/kern_fork.c Sat Jun 30 15:07:44 2018 (r335820)
@@ -736,18 +736,6 @@ do_fork(struct thread *td, struct fork_req *fr, struct
* but before we wait for the debugger.
*/
_PHOLD(p2);
- if (p1->p_ptevents & PTRACE_FORK) {
- /*
- * Arrange for debugger to receive the fork event.
- *
- * We can report PL_FLAG_FORKED regardless of
- * P_FOLLOWFORK settings, but it does not make a sense
- * for runaway child.
- */
- td->td_dbgflags |= TDB_FORK;
- td->td_dbg_forked = p2->p_pid;
- td2->td_dbgflags |= TDB_STOPATFORK;
- }
if (fr->fr_flags & RFPPWAIT) {
td->td_pflags |= TDP_RFPPWAIT;
td->td_rfppwait_p = p2;
@@ -771,7 +759,42 @@ do_fork(struct thread *td, struct fork_req *fr, struct
procdesc_finit(p2->p_procdesc, fp_procdesc);
fdrop(fp_procdesc, td);
}
-
+
+ /*
+ * Speculative check for PTRACE_FORK. PTRACE_FORK is not
+ * synced with forks in progress so it is OK if we miss it
+ * if being set atm.
+ */
+ if ((p1->p_ptevents & PTRACE_FORK) != 0) {
+ sx_xlock(&proctree_lock);
+ PROC_LOCK(p2);
+
+ /*
+ * p1->p_ptevents & p1->p_pptr are protected by both
+ * process and proctree locks for modifications,
+ * so owning proctree_lock allows the race-free read.
+ */
+ if ((p1->p_ptevents & PTRACE_FORK) != 0) {
+ /*
+ * Arrange for debugger to receive the fork event.
+ *
+ * We can report PL_FLAG_FORKED regardless of
+ * P_FOLLOWFORK settings, but it does not make a sense
+ * for runaway child.
+ */
+ td->td_dbgflags |= TDB_FORK;
+ td->td_dbg_forked = p2->p_pid;
+ td2->td_dbgflags |= TDB_STOPATFORK;
+ proc_set_traced(p2, true);
+ CTR2(KTR_PTRACE,
+ "do_fork: attaching to new child pid %d: oppid %d",
+ p2->p_pid, p2->p_oppid);
+ proc_reparent(p2, p1->p_pptr);
+ }
+ PROC_UNLOCK(p2);
+ sx_xunlock(&proctree_lock);
+ }
+
if ((fr->fr_flags & RFSTOPPED) == 0) {
/*
* If RFSTOPPED not requested, make child runnable and
@@ -788,11 +811,6 @@ do_fork(struct thread *td, struct fork_req *fr, struct
}
PROC_LOCK(p2);
- /*
- * Wait until debugger is attached to child.
- */
- while (td2->td_proc == p2 && (td2->td_dbgflags & TDB_STOPATFORK) != 0)
- cv_wait(&p2->p_dbgwait, &p2->p_mtx);
_PRELE(p2);
racct_proc_fork_done(p2);
PROC_UNLOCK(p2);
@@ -1078,24 +1096,15 @@ fork_exit(void (*callout)(void *, struct trapframe *),
void
fork_return(struct thread *td, struct trapframe *frame)
{
- struct proc *p, *dbg;
+ struct proc *p;
p = td->td_proc;
if (td->td_dbgflags & TDB_STOPATFORK) {
- sx_xlock(&proctree_lock);
PROC_LOCK(p);
- if (p->p_pptr->p_ptevents & PTRACE_FORK) {
+ if ((p->p_flag & P_TRACED) != 0) {
/*
- * If debugger still wants auto-attach for the
- * parent's children, do it now.
+ * Inform the debugger if one is still present.
*/
- dbg = p->p_pptr->p_pptr;
- proc_set_traced(p, true);
- CTR2(KTR_PTRACE,
- "fork_return: attaching to new child pid %d: oppid %d",
- p->p_pid, p->p_oppid);
- proc_reparent(p, dbg);
- sx_xunlock(&proctree_lock);
td->td_dbgflags |= TDB_CHILD | TDB_SCX | TDB_FSTP;
ptracestop(td, SIGSTOP, NULL);
td->td_dbgflags &= ~(TDB_CHILD | TDB_SCX);
@@ -1103,9 +1112,7 @@ fork_return(struct thread *td, struct trapframe *frame
/*
* ... otherwise clear the request.
*/
- sx_xunlock(&proctree_lock);
td->td_dbgflags &= ~TDB_STOPATFORK;
- cv_broadcast(&p->p_dbgwait);
}
PROC_UNLOCK(p);
} else if (p->p_flag & P_TRACED || td->td_dbgflags & TDB_BORN) {
Modified: stable/11/sys/kern/kern_proc.c
==============================================================================
--- stable/11/sys/kern/kern_proc.c Sat Jun 30 15:03:22 2018 (r335819)
+++ stable/11/sys/kern/kern_proc.c Sat Jun 30 15:07:44 2018 (r335820)
@@ -265,7 +265,6 @@ proc_init(void *mem, int size, int flags)
mtx_init(&p->p_itimmtx, "pitiml", NULL, MTX_SPIN | MTX_NEW);
mtx_init(&p->p_profmtx, "pprofl", NULL, MTX_SPIN | MTX_NEW);
cv_init(&p->p_pwait, "ppwait");
- cv_init(&p->p_dbgwait, "dbgwait");
TAILQ_INIT(&p->p_threads); /* all threads in proc */
EVENTHANDLER_DIRECT_INVOKE(process_init, p);
p->p_stats = pstats_alloc();
Modified: stable/11/sys/kern/kern_sig.c
==============================================================================
--- stable/11/sys/kern/kern_sig.c Sat Jun 30 15:03:22 2018 (r335819)
+++ stable/11/sys/kern/kern_sig.c Sat Jun 30 15:07:44 2018 (r335820)
@@ -2590,7 +2590,6 @@ ptracestop(struct thread *td, int sig, ksiginfo_t *si)
}
if ((td->td_dbgflags & TDB_STOPATFORK) != 0) {
td->td_dbgflags &= ~TDB_STOPATFORK;
- cv_broadcast(&p->p_dbgwait);
}
stopme:
thread_suspend_switch(td, p);
Modified: stable/11/sys/sys/proc.h
==============================================================================
--- stable/11/sys/sys/proc.h Sat Jun 30 15:03:22 2018 (r335819)
+++ stable/11/sys/sys/proc.h Sat Jun 30 15:07:44 2018 (r335820)
@@ -655,8 +655,7 @@ struct proc {
LIST_HEAD(, mqueue_notifier) p_mqnotifier; /* (c) mqueue notifiers.*/
struct kdtrace_proc *p_dtrace; /* (*) DTrace-specific data. */
struct cv p_pwait; /* (*) wait cv for exit/exec. */
- struct cv p_dbgwait; /* (*) wait cv for debugger attach
- after fork. */
+ struct cv p_pad_dbgwait;
uint64_t p_prev_runtime; /* (c) Resource usage accounting. */
struct racct *p_racct; /* (b) Resource accounting. */
int p_throttled; /* (c) Flag for racct pcpu throttling */
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