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Date:      Wed, 29 May 2019 14:05:27 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r348360 - head/sys/kern
Message-ID:  <201905291405.x4TE5RSD023376@repo.freebsd.org>
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Author: kib
Date: Wed May 29 14:05:27 2019
New Revision: 348360
URL: https://svnweb.freebsd.org/changeset/base/348360

Log:
  Do not go into sleep in sleepq_catch_signals() when SIGSTOP from
  PT_ATTACH was consumed.
  
  In particular, do not clear TDP_FSTP in ptracestop() if td_wchan is
  non-NULL. Leave it to sleepq_catch_signal() to clear and convert zero
  return code to EINTR.
  
  Otherwise, per submitter report, if the PT_ATTACH SIGSTOP was
  delivered right after the thread was added to the sleepqueue but not
  yet really sleep, and cursig() caused debugger attach, the thread
  sleeps instead of returning to the userspace boundary with EINTR.
  
  PR: 231445
  Reported by:	Efi Weiss <valmarelox@gmail.com>
  Reviewed by:	markj
  Sponsored by:	The FreeBSD Foundation
  MFC after:	2 weeks
  Differential revision:	https://reviews.freebsd.org/D20381

Modified:
  head/sys/kern/kern_sig.c
  head/sys/kern/subr_sleepqueue.c

Modified: head/sys/kern/kern_sig.c
==============================================================================
--- head/sys/kern/kern_sig.c	Wed May 29 13:51:18 2019	(r348359)
+++ head/sys/kern/kern_sig.c	Wed May 29 14:05:27 2019	(r348360)
@@ -2576,7 +2576,15 @@ ptracestop(struct thread *td, int sig, ksiginfo_t *si)
 			    p->p_xthread == NULL)) {
 				p->p_xsig = sig;
 				p->p_xthread = td;
-				td->td_dbgflags &= ~TDB_FSTP;
+
+				/*
+				 * If we are on sleepqueue already,
+				 * let sleepqueue code decide if it
+				 * needs to go sleep after attach.
+				 */
+				if (td->td_wchan == NULL)
+					td->td_dbgflags &= ~TDB_FSTP;
+
 				p->p_flag2 &= ~P2_PTRACE_FSTP;
 				p->p_flag |= P_STOPPED_SIG | P_STOPPED_TRACE;
 				sig_suspend_threads(td, p, 0);

Modified: head/sys/kern/subr_sleepqueue.c
==============================================================================
--- head/sys/kern/subr_sleepqueue.c	Wed May 29 13:51:18 2019	(r348359)
+++ head/sys/kern/subr_sleepqueue.c	Wed May 29 14:05:27 2019	(r348360)
@@ -498,6 +498,19 @@ sleepq_catch_signals(void *wchan, int pri)
 			} else {
 				mtx_unlock(&ps->ps_mtx);
 			}
+
+			/*
+			 * Do not go into sleep if this thread was the
+			 * ptrace(2) attach leader.  cursig() consumed
+			 * SIGSTOP from PT_ATTACH, but we usually act
+			 * on the signal by interrupting sleep, and
+			 * should do that here as well.
+			 */
+			if ((td->td_dbgflags & TDB_FSTP) != 0) {
+				if (ret == 0)
+					ret = EINTR;
+				td->td_dbgflags &= ~TDB_FSTP;
+			}
 		}
 		/*
 		 * Lock the per-process spinlock prior to dropping the PROC_LOCK

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