Author: kib Date: Thu Jun 21 21:12:49 2018 New Revision: 335504 URL: https://svnweb.freebsd.org/changeset/base/335504
Log: fork: avoid endless wait with PTRACE_FORK and RFSTOPPED. An RFSTOPPED thread can't clean TDB_STOPATFORK, which is done in the fork_return() in its context, so parent is stuck forever. Triggered when trying to ptrace linux process. Instead of waiting for the new thread to clear TDB_STOPATFORK, tag it as traced and reparent to the debugger in do_fork(), and let it only notify the debugger when run. Submitted by: Yanko Yankulov <yanko.yanku...@gmail.com> Reviewed by: jhb MFC after: 1 week X-MFC-Note: keep p_dbgwait placeholder intact Differential revision: https://reviews.freebsd.org/D15857 Modified: head/sys/kern/kern_fork.c head/sys/kern/kern_proc.c head/sys/kern/kern_sig.c head/sys/sys/proc.h Modified: head/sys/kern/kern_fork.c ============================================================================== --- head/sys/kern/kern_fork.c Thu Jun 21 21:07:25 2018 (r335503) +++ head/sys/kern/kern_fork.c Thu Jun 21 21:12:49 2018 (r335504) @@ -721,18 +721,6 @@ 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; @@ -756,7 +744,42 @@ 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 @@ -773,11 +796,6 @@ 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); @@ -1063,24 +1081,15 @@ 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); @@ -1088,9 +1097,7 @@ 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: head/sys/kern/kern_proc.c ============================================================================== --- head/sys/kern/kern_proc.c Thu Jun 21 21:07:25 2018 (r335503) +++ head/sys/kern/kern_proc.c Thu Jun 21 21:12:49 2018 (r335504) @@ -266,7 +266,6 @@ 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: head/sys/kern/kern_sig.c ============================================================================== --- head/sys/kern/kern_sig.c Thu Jun 21 21:07:25 2018 (r335503) +++ head/sys/kern/kern_sig.c Thu Jun 21 21:12:49 2018 (r335504) @@ -2581,7 +2581,6 @@ 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: head/sys/sys/proc.h ============================================================================== --- head/sys/sys/proc.h Thu Jun 21 21:07:25 2018 (r335503) +++ head/sys/sys/proc.h Thu Jun 21 21:12:49 2018 (r335504) @@ -685,8 +685,6 @@ 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. */ 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 */ _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
