[01/19] nptl: Fix testcases for new pthread cancellation mechanism

Message ID 1513019223-7603-2-git-send-email-adhemerval.zanella@linaro.org
State New
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Series
  • nptl: Fix Race conditions in pthread cancellation (BZ#12683)
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Commit Message

Adhemerval Zanella Dec. 11, 2017, 7:06 p.m.
From: Adhemerval Zanella <adhemerval.zanella@linaro.com>


With upcoming fix for BZ#12683, pthread cancellation does not act for:

  1. If syscall is blocked but with some side effects already having
     taken place (e.g. a partial read or write).
  2. After the syscall has returned.

The main change is due the fact programs need to act in syscalls with
side-effects (for instance, to avoid leak of allocated resources or
handle partial read/write).

This patch changes the NPTL testcase that assumes the old behavior and
also remove the tst-cancel-wrappers.sh test (which checks for symbols
that will not exist anymore).  For tst-cancel{2,3} case it remove the
pipe close because it might cause the write syscall to return with
side effects if the close is executed before the pthread cancel.

It also changes how to call the read syscall on tst-backtrace{5,6}
to use syscall instead of read cancelable syscall to avoid need to
handle the cancelable bridge function calls.  It requires a change
on powerpc syscall implementation to create a stackframe, since
powerpc backtrace rely on such information.

Checked on i686-linux-gnu, x86_64-linux-gnu, x86_64-linux-gnux32,
aarch64-linux-gnu, arm-linux-gnueabihf, powerpc64le-linux-gnu,
powerpc-linux-gnu, sparcv9-linux-gnu, and sparc64-linux-gnu.

	* debug/tst-backtrace5.c (handle_signal): Check for syscall
	instead of read.
	(fn): Issue the read syscall instead of call the cancellable
	syscall.
	* nptl/Makefile [$(run-built-tests) = yes] (tests-special): Remove
	tst-cancel-wrappers.sh.
	* nptl/tst-cancel-wrappers.sh: Remove file.
	* nptl/tst-cancel2.c (do_test): Do not close pipe.
	* nptl/tst-cancel3.c (do_test): Likewise.
	* nptl/tst-cancel4.c (tf_write): Handle cancelled syscall with
	side-effects.
	(tf_send): Likewise.
	* sysdeps/unix/sysv/linux/powerpc/syscall.S (syscall): Create stack
	frame.

Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

---
 ChangeLog                                 | 17 ++++++
 debug/tst-backtrace5.c                    | 26 +++++----
 nptl/Makefile                             | 17 +-----
 nptl/tst-cancel-wrappers.sh               | 92 -------------------------------
 nptl/tst-cancel2.c                        |  3 -
 nptl/tst-cancel3.c                        |  3 -
 nptl/tst-cancel4.c                        |  8 +++
 sysdeps/unix/sysv/linux/powerpc/syscall.S | 14 +++++
 8 files changed, 57 insertions(+), 123 deletions(-)
 delete mode 100644 nptl/tst-cancel-wrappers.sh

-- 
2.7.4

Comments

Florian Weimer Dec. 12, 2017, 12:18 p.m. | #1
On 12/11/2017 08:06 PM, Adhemerval Zanella wrote:
> It also changes how to call the read syscall on tst-backtrace{5,6}

> to use syscall instead of read cancelable syscall to avoid need to

> handle the cancelable bridge function calls.  It requires a change

> on powerpc syscall implementation to create a stackframe, since

> powerpc backtrace rely on such information.


The powerpc is a separate change and should go in separately, with a 
separate bug number, IMHO.

The existence of this bug also suggests to me that you're patching the 
test to check something else, so maybe we need better backtrace testing 
coverage for more syscall implementation variants.  But that's just an 
aside.

 > +	/* Creates a minimum stack frame so backtrace.  */


“so backtrace works”?

> +#ifdef __powerpc64__

> +	addi r1, r1, FRAME_MIN_SIZE

> +#else

> +	addi r1,r1,16

> +#endif

> +        cfi_def_cfa_offset (0)

>  	sc


I find the extent of this pseudo-stack frame rather puzzling.

Thanks,
Florian
Adhemerval Zanella Dec. 12, 2017, 12:27 p.m. | #2
On 12/12/2017 10:18, Florian Weimer wrote:
> On 12/11/2017 08:06 PM, Adhemerval Zanella wrote:

>> It also changes how to call the read syscall on tst-backtrace{5,6}

>> to use syscall instead of read cancelable syscall to avoid need to

>> handle the cancelable bridge function calls.  It requires a change

>> on powerpc syscall implementation to create a stackframe, since

>> powerpc backtrace rely on such information.

> 

> The powerpc is a separate change and should go in separately, with a separate bug number, IMHO.


Alright I can split the powerpc change on a different path.

> 

> The existence of this bug also suggests to me that you're patching the test to check something else, so maybe we need better backtrace testing coverage for more syscall implementation variants.  But that's just an aside.


The test still check backtrace across signal frames, I changed it to use
syscall (...) instead of a direct wrapper call mainly to make it work on
both current implementation and newer one.

Another possible option is to rewrite the test and add it on my
02/19 patch to take in account the new backtrace layout. 

> 

>> +    /* Creates a minimum stack frame so backtrace.  */

> 

> “so backtrace works”?

> 

>> +#ifdef __powerpc64__

>> +    addi r1, r1, FRAME_MIN_SIZE

>> +#else

>> +    addi r1,r1,16

>> +#endif

>> +        cfi_def_cfa_offset (0)

>>      sc

> 

> I find the extent of this pseudo-stack frame rather puzzling.


This is mainly to make our backtrace.c implementation on powerpc
to get the frame that actually called syscall (...).  Current
powerpc just check the stacktrace on *sp, so there is no need
fully frame pointer info generated by -fno-omit-frame pointer.

Patch

diff --git a/debug/tst-backtrace5.c b/debug/tst-backtrace5.c
index 0b85e44..0ef2627 100644
--- a/debug/tst-backtrace5.c
+++ b/debug/tst-backtrace5.c
@@ -23,6 +23,7 @@ 
 #include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>
+#include <sys/syscall.h>
 #include <signal.h>
 #include <unistd.h>
 
@@ -33,7 +34,7 @@ 
 #endif
 
 /* The backtrace should include at least handle_signal, a signal
-   trampoline, read, 3 * fn, and do_test.  */
+   trampoline, syscall, 3 * fn, and do_test.  */
 #define NUM_FUNCTIONS 7
 
 void
@@ -71,15 +72,17 @@  handle_signal (int signum)
     }
   /* Do not check name for signal trampoline.  */
   i = 2;
-  if (!match (symbols[i++], "read"))
+
+  if (match (symbols[i], "__kernel_vsyscall"))
+    i++;
+
+  /* We are using syscall(...) instead of read.  */
+  if (!match (symbols[i++], "syscall"))
     {
-      /* Perhaps symbols[2] is __kernel_vsyscall?  */
-      if (!match (symbols[i++], "read"))
-	{
-	  FAIL ();
-	  return;
-	}
+      FAIL ();
+      return;
     }
+
   for (; i < n - 1; i++)
     if (!match (symbols[i], "fn"))
       {
@@ -123,8 +126,11 @@  fn (int c, int flags)
       _exit (0);
     }
 
-  /* In the parent.  */
-  read (pipefd[0], r, 1);
+  /* To avoid need to handle cancellation syscall backtrace (which call
+     the function using both the generic bridge (__syscall_cancel) and
+     the architecture defined one (__syscall_cancel_arch), issue the
+     syscall directly.  */
+  syscall (__NR_read, pipefd[0], r, 1);
 
   return 0;
 }
diff --git a/nptl/Makefile b/nptl/Makefile
index 11e6ecd..36bf25f 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -445,8 +445,7 @@  tests-reverse += tst-cancel5 tst-cancel23 tst-vfork1x tst-vfork2x
 ifeq ($(run-built-tests),yes)
 tests-special += $(objpfx)tst-stack3-mem.out $(objpfx)tst-oddstacklimit.out
 ifeq ($(build-shared),yes)
-tests-special += $(objpfx)tst-tls6.out $(objpfx)tst-cleanup0-cmp.out \
-		 $(objpfx)tst-cancel-wrappers.out
+tests-special += $(objpfx)tst-tls6.out $(objpfx)tst-cleanup0-cmp.out
 endif
 endif
 
@@ -670,7 +669,7 @@  $(objpfx)$(multidir)/crtn.o: $(objpfx)crtn.o $(objpfx)$(multidir)/
 endif
 
 generated += libpthread_nonshared.a \
-	     multidir.mk tst-atfork2.mtrace tst-cancel-wrappers.out \
+	     multidir.mk tst-atfork2.mtrace \
 	     tst-tls6.out
 
 generated += $(objpfx)tst-atfork2.mtrace \
@@ -682,18 +681,6 @@  LDFLAGS-pthread.so += -e __nptl_main
 $(objpfx)pt-interp.os: $(common-objpfx)runtime-linker.h
 endif
 
-ifeq ($(run-built-tests),yes)
-ifeq (yes,$(build-shared))
-$(objpfx)tst-cancel-wrappers.out: tst-cancel-wrappers.sh
-	$(SHELL) $< '$(NM)' \
-		    $(common-objpfx)libc_pic.a \
-		    $(common-objpfx)libc.a \
-		    $(objpfx)libpthread_pic.a \
-		    $(objpfx)libpthread.a > $@; \
-	$(evaluate-test)
-endif
-endif
-
 tst-exec4-ARGS = $(host-test-program-cmd)
 
 $(objpfx)tst-execstack: $(libdl)
diff --git a/nptl/tst-cancel-wrappers.sh b/nptl/tst-cancel-wrappers.sh
deleted file mode 100644
index 1795e3d..0000000
--- a/nptl/tst-cancel-wrappers.sh
+++ /dev/null
@@ -1,92 +0,0 @@ 
-#!/bin/sh
-# Test whether all cancelable functions are cancelable.
-# Copyright (C) 2002-2017 Free Software Foundation, Inc.
-# This file is part of the GNU C Library.
-# Contributed by Jakub Jelinek <jakub@redhat.com>, 2002.
-
-# The GNU C Library is free software; you can redistribute it and/or
-# modify it under the terms of the GNU Lesser General Public
-# License as published by the Free Software Foundation; either
-# version 2.1 of the License, or (at your option) any later version.
-
-# The GNU C Library is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-# Lesser General Public License for more details.
-
-# You should have received a copy of the GNU Lesser General Public
-# License along with the GNU C Library; if not, see
-# <http://www.gnu.org/licenses/>.
-
-NM="$1"; shift
-while [ $# -gt 0 ]; do
-  ( $NM -P $1; echo 'end[end]:' ) | gawk ' BEGIN {
-C["accept"]=1
-C["close"]=1
-C["connect"]=1
-C["creat"]=1
-C["fcntl"]=1
-C["fdatasync"]=1
-C["fsync"]=1
-C["msgrcv"]=1
-C["msgsnd"]=1
-C["msync"]=1
-C["nanosleep"]=1
-C["open"]=1
-C["open64"]=1
-C["pause"]=1
-C["poll"]=1
-C["pread"]=1
-C["pread64"]=1
-C["pselect"]=1
-C["pwrite"]=1
-C["pwrite64"]=1
-C["read"]=1
-C["readv"]=1
-C["recv"]=1
-C["recvfrom"]=1
-C["recvmsg"]=1
-C["select"]=1
-C["send"]=1
-C["sendmsg"]=1
-C["sendto"]=1
-C["sigpause"]=1
-C["sigsuspend"]=1
-C["sigwait"]=1
-C["sigwaitinfo"]=1
-C["tcdrain"]=1
-C["wait"]=1
-C["waitid"]=1
-C["waitpid"]=1
-C["write"]=1
-C["writev"]=1
-C["__xpg_sigpause"]=1
-}
-/:$/ {
-  if (seen)
-    {
-      if (!seen_enable || !seen_disable)
-	{
-	  printf "in '$1'(%s) %s'\''s cancellation missing\n", object, seen
-	  ret = 1
-	}
-    }
-  seen=""
-  seen_enable=""
-  seen_disable=""
-  object=gensub(/^.*\[(.*)\]:$/, "\\1", 1, $0)
-  next
-}
-{
-  if (C[$1] && $2 ~ /^[TW]$/)
-    seen=$1
-  else if ($1 ~ /^([.]|)__(libc|pthread)_enable_asynccancel$/ && $2 == "U")
-    seen_enable=1
-  else if ($1 ~ /^([.]|)__(libc|pthread)_disable_asynccancel$/ && $2 == "U")
-    seen_disable=1
-}
-END {
-  exit ret
-}' || exit
-  shift
-done
diff --git a/nptl/tst-cancel2.c b/nptl/tst-cancel2.c
index bf7946c..25a6143 100644
--- a/nptl/tst-cancel2.c
+++ b/nptl/tst-cancel2.c
@@ -73,9 +73,6 @@  do_test (void)
       return 1;
     }
 
-  /* This will cause the write in the child to return.  */
-  close (fd[0]);
-
   if (pthread_join (th, &r) != 0)
     {
       puts ("join failed");
diff --git a/nptl/tst-cancel3.c b/nptl/tst-cancel3.c
index 228c478..c462a7e 100644
--- a/nptl/tst-cancel3.c
+++ b/nptl/tst-cancel3.c
@@ -75,9 +75,6 @@  do_test (void)
       return 1;
     }
 
-  /* This will cause the read in the child to return.  */
-  close (fd[0]);
-
   if (pthread_join (th, &r) != 0)
     {
       puts ("join failed");
diff --git a/nptl/tst-cancel4.c b/nptl/tst-cancel4.c
index 7a560a1..4f21131 100644
--- a/nptl/tst-cancel4.c
+++ b/nptl/tst-cancel4.c
@@ -166,6 +166,10 @@  tf_write  (void *arg)
   char buf[WRITE_BUFFER_SIZE];
   memset (buf, '\0', sizeof (buf));
   s = write (fd, buf, sizeof (buf));
+  /* The write can return a value higher than 0 (meaning partial write)
+     due to the SIGCANCEL, but the thread may still be pending
+     cancellation.  */
+  pthread_testcancel ();
 
   pthread_cleanup_pop (0);
 
@@ -742,6 +746,10 @@  tf_send (void *arg)
   char mem[700000];
 
   send (tempfd2, mem, arg == NULL ? sizeof (mem) : 1, 0);
+  /* Thez send can return a value higher than 0 (meaning partial send)
+     due to the SIGCANCEL, but the thread may still be pending
+     cancellation.  */
+  pthread_testcancel ();
 
   pthread_cleanup_pop (0);
 
diff --git a/sysdeps/unix/sysv/linux/powerpc/syscall.S b/sysdeps/unix/sysv/linux/powerpc/syscall.S
index 0522ccd..9fa64d9 100644
--- a/sysdeps/unix/sysv/linux/powerpc/syscall.S
+++ b/sysdeps/unix/sysv/linux/powerpc/syscall.S
@@ -19,6 +19,14 @@ 
 
 ENTRY (syscall)
 	ABORT_TRANSACTION
+	/* Creates a minimum stack frame so backtrace.  */
+#ifdef __powerpc64__
+	stdu r1, -FRAME_MIN_SIZE (r1)
+	cfi_adjust_cfa_offset (FRAME_MIN_SIZE)
+#else
+	stwu r1,-16(1)
+	cfi_def_cfa_offset (16)
+#endif
 	mr   r0,r3
 	mr   r3,r4
 	mr   r4,r5
@@ -26,6 +34,12 @@  ENTRY (syscall)
 	mr   r6,r7
 	mr   r7,r8
 	mr   r8,r9
+#ifdef __powerpc64__
+	addi r1, r1, FRAME_MIN_SIZE
+#else
+	addi r1,r1,16
+#endif
+        cfi_def_cfa_offset (0)
 	sc
 	PSEUDO_RET
 PSEUDO_END (syscall)