commit 16adc58e73f3 (stdlib: Fix data race in __run_exit_handlers [BZ #27749])

commit 16adc58e73f3 (stdlib: Fix data race in __run_exit_handlers [BZ #27749])

[Rasmus Villemoes]

I think the commit in $subject is broken. I was browsing through the
atexit handling code and stumbled on something which is always a code
smell, namely the pattern

  if (whatever)
    continue;

at the end of a loop.

And indeed, since we no longer jump back to the outer loop and refetch
the list head, one can observe a change in behavior. This program:

#include <stdio.h>
#include <stdlib.h>

void h(void)
{
	printf("third: %s()\n", __func__);
}
void j(void)
{
	printf("second: %s()\n", __func__);
}

void g(void)
{
	printf("first: %s()\n", __func__);
	atexit(h);
	atexit(j);
}
void f(void) {
	static int c;
	printf("%s: %d\n", __func__, ++c);
}

int main(int argc, char *argv[])
{
	int i;

	/*
	 * Stuff the "struct exit_function_list" with dummy callbacks;
	 * 30 may need to be adjusted depending on how many atexit()
	 * registrations libc itself does.
	 */
	for (i = 0; i < 30; ++i)
		atexit(f);

	/* Register one more, to fill the last slot in struct
exit_function_list. */
	atexit(g);
	
	return 0;
}

used to print

first: g()
second: j()
third: h()
f: 1
...
f: 30

but now it instead prints

first: g()
third: h()
f: 1
...
f: 30
second: j()


Rasmus

Re: commit 16adc58e73f3 (stdlib: Fix data race in __run_exit_handlers [BZ #27749])

[Vitaly Buka]

[-- Attachment #1: Type: text/plain, Size: 1637 bytes --]

Not sure how this happened, but it was not on my patch
https://sourceware.org/pipermail/libc-alpha/2021-April/125470.html

On Sun, 12 Feb 2023 at 15:44, Rasmus Villemoes <rasmus.villemoes@prevas.dk>
wrote:

> I think the commit in $subject is broken. I was browsing through the
> atexit handling code and stumbled on something which is always a code
> smell, namely the pattern
>
>   if (whatever)
>     continue;
>
> at the end of a loop.
>
> And indeed, since we no longer jump back to the outer loop and refetch
> the list head, one can observe a change in behavior. This program:
>
> #include <stdio.h>
> #include <stdlib.h>
>
> void h(void)
> {
>         printf("third: %s()\n", __func__);
> }
> void j(void)
> {
>         printf("second: %s()\n", __func__);
> }
>
> void g(void)
> {
>         printf("first: %s()\n", __func__);
>         atexit(h);
>         atexit(j);
> }
> void f(void) {
>         static int c;
>         printf("%s: %d\n", __func__, ++c);
> }
>
> int main(int argc, char *argv[])
> {
>         int i;
>
>         /*
>          * Stuff the "struct exit_function_list" with dummy callbacks;
>          * 30 may need to be adjusted depending on how many atexit()
>          * registrations libc itself does.
>          */
>         for (i = 0; i < 30; ++i)
>                 atexit(f);
>
>         /* Register one more, to fill the last slot in struct
> exit_function_list. */
>         atexit(g);
>
>         return 0;
> }
>
> used to print
>
> first: g()
> second: j()
> third: h()
> f: 1
> ...
> f: 30
>
> but now it instead prints
>
> first: g()
> third: h()
> f: 1
> ...
> f: 30
> second: j()
>
>
> Rasmus
>

[PATCH] stdlib: Undo post review change to 16adc58e73f3 [BZ #27749]

[Vitaly Buka]

Post review removal of "goto restart" from
https://sourceware.org/pipermail/libc-alpha/2021-April/125470.html
introduced a bug when some atexit handers skipped.

Signed-off-by: Vitaly Buka <vitalybuka@google.com>
---
 stdlib/Makefile                |  1 +
 stdlib/exit.c                  |  7 +++-
 stdlib/test-atexit-recursive.c | 72 ++++++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+), 2 deletions(-)
 create mode 100644 stdlib/test-atexit-recursive.c

diff --git a/stdlib/Makefile b/stdlib/Makefile
index 83391d00c1..8f80571d76 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -171,6 +171,7 @@ tests := \
   test-a64l \
   test-at_quick_exit-race \
   test-atexit-race \
+  test-atexit-recursive \
   test-bz22786 \
   test-canon \
   test-canon2 \
diff --git a/stdlib/exit.c b/stdlib/exit.c
index 6b1eed6445..1cd0bdfe94 100644
--- a/stdlib/exit.c
+++ b/stdlib/exit.c
@@ -51,7 +51,10 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
      exit (). */
   while (true)
     {
-      struct exit_function_list *cur = *listp;
+      struct exit_function_list *cur;
+
+    restart:
+      cur = *listp;
 
       if (cur == NULL)
 	{
@@ -113,7 +116,7 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
 	  if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called))
 	    /* The last exit function, or another thread, has registered
 	       more exit functions.  Start the loop over.  */
-            continue;
+	    goto restart;
 	}
 
       *listp = cur->next;
diff --git a/stdlib/test-atexit-recursive.c b/stdlib/test-atexit-recursive.c
new file mode 100644
index 0000000000..ca832941fe
--- /dev/null
+++ b/stdlib/test-atexit-recursive.c
@@ -0,0 +1,72 @@
+/* Support file for atexit/exit, etc. race tests (BZ #27749).
+   Copyright (C) 2021-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+/* Check that atexit handler registed from another handler still called. */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+static void
+atexit_cb (void) {
+}
+
+static void
+atexit_last (void) {
+  _exit (1);
+}
+
+static void
+atexit_recursive (void) {
+  atexit(&atexit_cb);
+  atexit(&atexit_last);
+}
+
+_Noreturn static void
+test_and_exit (int count)
+{
+  for (int i = 0; i < count; ++i)
+      atexit(&atexit_cb);
+  atexit(&atexit_recursive);
+  exit (0);
+}
+
+static int
+do_test (void)
+{
+  for (int i = 0; i < 100; ++i)
+    if (xfork () == 0)
+      test_and_exit (i);
+
+  for (int i = 0; i < 100; ++i)
+    {
+      int status;
+      xwaitpid (0, &status, 0);
+      if (!WIFEXITED (status))
+        FAIL_EXIT1 ("Failed iterations %d", i);
+      TEST_COMPARE (WEXITSTATUS (status), 1);
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test
+#include <support/test-driver.c>
-- 
2.39.1.581.gbfd45094c4-goog

[PATCH] stdlib: Undo post review change to 16adc58e73f3 [BZ #27749]

[Vitaly Buka]

Post review removal of "goto restart" from
https://sourceware.org/pipermail/libc-alpha/2021-April/125470.html
introduced a bug when some atexit handers skipped.

Signed-off-by: Vitaly Buka <vitalybuka@google.com>
---
 stdlib/Makefile                |  1 +
 stdlib/exit.c                  |  7 +++-
 stdlib/test-atexit-recursive.c | 72 ++++++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+), 2 deletions(-)
 create mode 100644 stdlib/test-atexit-recursive.c

diff --git a/stdlib/Makefile b/stdlib/Makefile
index 83391d00c1..8f80571d76 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -171,6 +171,7 @@ tests := \
   test-a64l \
   test-at_quick_exit-race \
   test-atexit-race \
+  test-atexit-recursive \
   test-bz22786 \
   test-canon \
   test-canon2 \
diff --git a/stdlib/exit.c b/stdlib/exit.c
index 6b1eed6445..1cd0bdfe94 100644
--- a/stdlib/exit.c
+++ b/stdlib/exit.c
@@ -51,7 +51,10 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
      exit (). */
   while (true)
     {
-      struct exit_function_list *cur = *listp;
+      struct exit_function_list *cur;
+
+    restart:
+      cur = *listp;
 
       if (cur == NULL)
 	{
@@ -113,7 +116,7 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
 	  if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called))
 	    /* The last exit function, or another thread, has registered
 	       more exit functions.  Start the loop over.  */
-            continue;
+	    goto restart;
 	}
 
       *listp = cur->next;
diff --git a/stdlib/test-atexit-recursive.c b/stdlib/test-atexit-recursive.c
new file mode 100644
index 0000000000..ca832941fe
--- /dev/null
+++ b/stdlib/test-atexit-recursive.c
@@ -0,0 +1,72 @@
+/* Support file for atexit/exit, etc. race tests (BZ #27749).
+   Copyright (C) 2021-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+/* Check that atexit handler registed from another handler still called. */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+static void
+atexit_cb (void) {
+}
+
+static void
+atexit_last (void) {
+  _exit (1);
+}
+
+static void
+atexit_recursive (void) {
+  atexit(&atexit_cb);
+  atexit(&atexit_last);
+}
+
+_Noreturn static void
+test_and_exit (int count)
+{
+  for (int i = 0; i < count; ++i)
+      atexit(&atexit_cb);
+  atexit(&atexit_recursive);
+  exit (0);
+}
+
+static int
+do_test (void)
+{
+  for (int i = 0; i < 100; ++i)
+    if (xfork () == 0)
+      test_and_exit (i);
+
+  for (int i = 0; i < 100; ++i)
+    {
+      int status;
+      xwaitpid (0, &status, 0);
+      if (!WIFEXITED (status))
+        FAIL_EXIT1 ("Failed iterations %d", i);
+      TEST_COMPARE (WEXITSTATUS (status), 1);
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test
+#include <support/test-driver.c>
-- 
2.39.1.581.gbfd45094c4-goog

Re: [PATCH] stdlib: Undo post review change to 16adc58e73f3 [BZ #27749]

[Adhemerval Zanella Netto]

On 13/02/23 03:01, Vitaly Buka wrote:
> Post review removal of "goto restart" from
> https://sourceware.org/pipermail/libc-alpha/2021-April/125470.html
> introduced a bug when some atexit handers skipped.
> 
> Signed-off-by: Vitaly Buka <vitalybuka@google.com>

Some minor issues on testcase style, besides that LGTM.  I am trying to
recall why I have pushed a slight different patch than the one you posted
on maillist (most likely my mistake).

> ---
>  stdlib/Makefile                |  1 +
>  stdlib/exit.c                  |  7 +++-
>  stdlib/test-atexit-recursive.c | 72 ++++++++++++++++++++++++++++++++++
>  3 files changed, 78 insertions(+), 2 deletions(-)
>  create mode 100644 stdlib/test-atexit-recursive.c
> 
> diff --git a/stdlib/Makefile b/stdlib/Makefile
> index 83391d00c1..8f80571d76 100644
> --- a/stdlib/Makefile
> +++ b/stdlib/Makefile
> @@ -171,6 +171,7 @@ tests := \
>    test-a64l \
>    test-at_quick_exit-race \
>    test-atexit-race \
> +  test-atexit-recursive \
>    test-bz22786 \
>    test-canon \
>    test-canon2 \
> diff --git a/stdlib/exit.c b/stdlib/exit.c
> index 6b1eed6445..1cd0bdfe94 100644
> --- a/stdlib/exit.c
> +++ b/stdlib/exit.c
> @@ -51,7 +51,10 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
>       exit (). */
>    while (true)
>      {
> -      struct exit_function_list *cur = *listp;
> +      struct exit_function_list *cur;
> +
> +    restart:
> +      cur = *listp;
>  
>        if (cur == NULL)
>  	{
> @@ -113,7 +116,7 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
>  	  if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called))
>  	    /* The last exit function, or another thread, has registered
>  	       more exit functions.  Start the loop over.  */
> -            continue;
> +	    goto restart;
>  	}
>  
>        *listp = cur->next;
> diff --git a/stdlib/test-atexit-recursive.c b/stdlib/test-atexit-recursive.c
> new file mode 100644
> index 0000000000..ca832941fe
> --- /dev/null
> +++ b/stdlib/test-atexit-recursive.c
> @@ -0,0 +1,72 @@
> +/* Support file for atexit/exit, etc. race tests (BZ #27749).
> +   Copyright (C) 2021-2023 Free Software Foundation, Inc.

Just 2023 here.

> +   This file is part of the GNU C Library.
> +
> +   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
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Check that atexit handler registed from another handler still called. */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <support/check.h>
> +#include <support/xunistd.h>
> +#include <sys/wait.h>
> +#include <unistd.h>
> +
> +static void
> +atexit_cb (void) {
> +}
> +

Open brackets in new line:

func (void)
{

> +static void
> +atexit_last (void) {
> +  _exit (1);
> +}
> +
> +static void
> +atexit_recursive (void) {
> +  atexit(&atexit_cb);

Space after function name.

> +  atexit(&atexit_last);
> +}
> +
> +_Noreturn static void
> +test_and_exit (int count)
> +{
> +  for (int i = 0; i < count; ++i)
> +      atexit(&atexit_cb);
> +  atexit(&atexit_recursive);
> +  exit (0);
> +}
> +
> +static int
> +do_test (void)
> +{
> +  for (int i = 0; i < 100; ++i)
> +    if (xfork () == 0)
> +      test_and_exit (i);
> +
> +  for (int i = 0; i < 100; ++i)
> +    {
> +      int status;
> +      xwaitpid (0, &status, 0);
> +      if (!WIFEXITED (status))
> +        FAIL_EXIT1 ("Failed iterations %d", i);
> +      TEST_COMPARE (WEXITSTATUS (status), 1);
> +    }
> +
> +  return 0;
> +}
> +
> +#define TEST_FUNCTION do_test

No need to define TEST_FUNCTION.

> +#include <support/test-driver.c>

[PATCH] stdlib: Undo post review change to 16adc58e73f3 [BZ #27749]

[Vitaly Buka]

Post review removal of "goto restart" from
https://sourceware.org/pipermail/libc-alpha/2021-April/125470.html
introduced a bug when some atexit handers skipped.

Signed-off-by: Vitaly Buka <vitalybuka@google.com>
---
 stdlib/Makefile                |  1 +
 stdlib/exit.c                  |  7 +++-
 stdlib/test-atexit-recursive.c | 75 ++++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+), 2 deletions(-)
 create mode 100644 stdlib/test-atexit-recursive.c

diff --git a/stdlib/Makefile b/stdlib/Makefile
index ff5096ad1b..cd32f53b56 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -171,6 +171,7 @@ tests := \
   test-a64l \
   test-at_quick_exit-race \
   test-atexit-race \
+  test-atexit-recursive \
   test-bz22786 \
   test-canon \
   test-canon2 \
diff --git a/stdlib/exit.c b/stdlib/exit.c
index 6b1eed6445..1cd0bdfe94 100644
--- a/stdlib/exit.c
+++ b/stdlib/exit.c
@@ -51,7 +51,10 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
      exit (). */
   while (true)
     {
-      struct exit_function_list *cur = *listp;
+      struct exit_function_list *cur;
+
+    restart:
+      cur = *listp;
 
       if (cur == NULL)
 	{
@@ -113,7 +116,7 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
 	  if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called))
 	    /* The last exit function, or another thread, has registered
 	       more exit functions.  Start the loop over.  */
-            continue;
+	    goto restart;
 	}
 
       *listp = cur->next;
diff --git a/stdlib/test-atexit-recursive.c b/stdlib/test-atexit-recursive.c
new file mode 100644
index 0000000000..0596b9763b
--- /dev/null
+++ b/stdlib/test-atexit-recursive.c
@@ -0,0 +1,75 @@
+/* Support file for atexit/exit, etc. race tests (BZ #27749).
+   Copyright (C) 2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+/* Check that atexit handler registed from another handler still called. */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+static void
+atexit_cb (void)
+{
+}
+
+static void
+atexit_last (void)
+{
+  _exit (1);
+}
+
+static void
+atexit_recursive (void)
+{
+  atexit (&atexit_cb);
+  atexit (&atexit_last);
+}
+
+_Noreturn static void
+test_and_exit (int count)
+{
+  for (int i = 0; i < count; ++i)
+    atexit (&atexit_cb);
+  atexit (&atexit_recursive);
+  exit (0);
+}
+
+static int
+do_test (void)
+{
+  for (int i = 0; i < 100; ++i)
+    if (xfork () == 0)
+      test_and_exit (i);
+
+  for (int i = 0; i < 100; ++i)
+    {
+      int status;
+      xwaitpid (0, &status, 0);
+      if (!WIFEXITED (status))
+	FAIL_EXIT1 ("Failed iterations %d", i);
+      TEST_COMPARE (WEXITSTATUS (status), 1);
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test
+#include <support/test-driver.c>
-- 
2.39.2.637.g21b0678d19-goog

Re: [PATCH] stdlib: Undo post review change to 16adc58e73f3 [BZ #27749]

[Adhemerval Zanella Netto]

On 18/02/23 17:53, Vitaly Buka wrote:
> Post review removal of "goto restart" from
> https://sourceware.org/pipermail/libc-alpha/2021-April/125470.html
> introduced a bug when some atexit handers skipped.
> 
> Signed-off-by: Vitaly Buka <vitalybuka@google.com>

LGTM, thanks.

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

> ---
>  stdlib/Makefile                |  1 +
>  stdlib/exit.c                  |  7 +++-
>  stdlib/test-atexit-recursive.c | 75 ++++++++++++++++++++++++++++++++++
>  3 files changed, 81 insertions(+), 2 deletions(-)
>  create mode 100644 stdlib/test-atexit-recursive.c
> 
> diff --git a/stdlib/Makefile b/stdlib/Makefile
> index ff5096ad1b..cd32f53b56 100644
> --- a/stdlib/Makefile
> +++ b/stdlib/Makefile
> @@ -171,6 +171,7 @@ tests := \
>    test-a64l \
>    test-at_quick_exit-race \
>    test-atexit-race \
> +  test-atexit-recursive \
>    test-bz22786 \
>    test-canon \
>    test-canon2 \
> diff --git a/stdlib/exit.c b/stdlib/exit.c
> index 6b1eed6445..1cd0bdfe94 100644
> --- a/stdlib/exit.c
> +++ b/stdlib/exit.c
> @@ -51,7 +51,10 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
>       exit (). */
>    while (true)
>      {
> -      struct exit_function_list *cur = *listp;
> +      struct exit_function_list *cur;
> +
> +    restart:
> +      cur = *listp;
>  
>        if (cur == NULL)
>  	{
> @@ -113,7 +116,7 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
>  	  if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called))
>  	    /* The last exit function, or another thread, has registered
>  	       more exit functions.  Start the loop over.  */
> -            continue;
> +	    goto restart;
>  	}
>  
>        *listp = cur->next;
> diff --git a/stdlib/test-atexit-recursive.c b/stdlib/test-atexit-recursive.c
> new file mode 100644
> index 0000000000..0596b9763b
> --- /dev/null
> +++ b/stdlib/test-atexit-recursive.c
> @@ -0,0 +1,75 @@
> +/* Support file for atexit/exit, etc. race tests (BZ #27749).
> +   Copyright (C) 2023 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   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
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Check that atexit handler registed from another handler still called. */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <support/check.h>
> +#include <support/xunistd.h>
> +#include <sys/wait.h>
> +#include <unistd.h>
> +
> +static void
> +atexit_cb (void)
> +{
> +}
> +
> +static void
> +atexit_last (void)
> +{
> +  _exit (1);
> +}
> +
> +static void
> +atexit_recursive (void)
> +{
> +  atexit (&atexit_cb);
> +  atexit (&atexit_last);
> +}
> +
> +_Noreturn static void
> +test_and_exit (int count)
> +{
> +  for (int i = 0; i < count; ++i)
> +    atexit (&atexit_cb);
> +  atexit (&atexit_recursive);
> +  exit (0);
> +}
> +
> +static int
> +do_test (void)
> +{
> +  for (int i = 0; i < 100; ++i)
> +    if (xfork () == 0)
> +      test_and_exit (i);
> +
> +  for (int i = 0; i < 100; ++i)
> +    {
> +      int status;
> +      xwaitpid (0, &status, 0);
> +      if (!WIFEXITED (status))
> +	FAIL_EXIT1 ("Failed iterations %d", i);
> +      TEST_COMPARE (WEXITSTATUS (status), 1);
> +    }
> +
> +  return 0;
> +}
> +
> +#define TEST_FUNCTION do_test
> +#include <support/test-driver.c>