stdlib: Fix data race in __run_exit_handlers
Commit Message
Fixes https://sourceware.org/bugzilla/show_bug.cgi?id=27749
Keep __exit_funcs_lock almost all the time and unlock it only to execute
callbacks. This fixed two issues.
1. f->func.cxa was modified outside the lock with rare data race like:
thread 0: __run_exit_handlers unlock __exit_funcs_lock
thread 1: __internal_atexit locks __exit_funcs_lock
thread 0: f->flavor = ef_free;
thread 1: sees ef_free and use it as new
thread 1: new->func.cxa.fn = (void (*) (void *, int)) func;
thread 1: new->func.cxa.arg = arg;
thread 1: new->flavor = ef_cxa;
thread 0: cxafct = f->func.cxa.fn; // it's wrong fn!
thread 0: cxafct (f->func.cxa.arg, status); // it's wrong arg!
thread 0: goto restart;
thread 0: call the same exit_function again as it's ef_cxa
2. Don't unlock in main while loop after *listp = cur->next. If *listp
is NULL and __exit_funcs_done is false another thread may fail in
__new_exitfn on assert (l != NULL):
thread 0: *listp = cur->next; // It can be the last: *listp = NULL.
thread 0: __libc_lock_unlock
thread 1: __libc_lock_lock in __on_exit
thread 1: __new_exitfn
thread 1: if (__exit_funcs_done) // false: thread 0 isn't there yet.
thread 1: l = *listp
thread 1: moves one and crashes on assert (l != NULL);
The test needs multiple iterations to consistently fail without the fix.
---
stdlib/Makefile | 4 +-
stdlib/exit.c | 28 ++++++---
stdlib/test-cxa_atexit-race2.c | 110 +++++++++++++++++++++++++++++++++
3 files changed, 131 insertions(+), 11 deletions(-)
create mode 100644 stdlib/test-cxa_atexit-race2.c
Comments
On 26/04/2021 16:27, Vitaly Buka via Libc-alpha wrote:
> Fixes https://sourceware.org/bugzilla/show_bug.cgi?id=27749
>
> Keep __exit_funcs_lock almost all the time and unlock it only to execute
> callbacks. This fixed two issues.
>
> 1. f->func.cxa was modified outside the lock with rare data race like:
> thread 0: __run_exit_handlers unlock __exit_funcs_lock
> thread 1: __internal_atexit locks __exit_funcs_lock
> thread 0: f->flavor = ef_free;
> thread 1: sees ef_free and use it as new
> thread 1: new->func.cxa.fn = (void (*) (void *, int)) func;
> thread 1: new->func.cxa.arg = arg;
> thread 1: new->flavor = ef_cxa;
> thread 0: cxafct = f->func.cxa.fn; // it's wrong fn!
> thread 0: cxafct (f->func.cxa.arg, status); // it's wrong arg!
> thread 0: goto restart;
> thread 0: call the same exit_function again as it's ef_cxa
Ok, the small window between fetching the function pointer and argument
from the list is triggering a race condition.
>
> 2. Don't unlock in main while loop after *listp = cur->next. If *listp
> is NULL and __exit_funcs_done is false another thread may fail in
> __new_exitfn on assert (l != NULL):
> thread 0: *listp = cur->next; // It can be the last: *listp = NULL.
> thread 0: __libc_lock_unlock
> thread 1: __libc_lock_lock in __on_exit
> thread 1: __new_exitfn
> thread 1: if (__exit_funcs_done) // false: thread 0 isn't there yet.
> thread 1: l = *listp
> thread 1: moves one and crashes on assert (l != NULL);
Yeah, this is tricky but it does look correct. I guess the lock/unlock
during the loop was added to give a chance to concurrent
__cxa_atexit / on_exit to have a chance to add a new callback, but it
also only complicates things as you noted. We might try to fix it on the
__new_exitfn (to avoid the assert), but I see the current approach of
locking the list and only unlocking while running the callback is the
right approach.
The patch look ok in general, I added some comments below. I have
adjusted the patch based on my comments [1], if you are ok with them
I can push it upstream.
[1] https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/azanella/bz27749-atexit-fix
>
> The test needs multiple iterations to consistently fail without the fix.
> ---
> stdlib/Makefile | 4 +-
> stdlib/exit.c | 28 ++++++---
> stdlib/test-cxa_atexit-race2.c | 110 +++++++++++++++++++++++++++++++++
> 3 files changed, 131 insertions(+), 11 deletions(-)
> create mode 100644 stdlib/test-cxa_atexit-race2.c
>
> diff --git a/stdlib/Makefile b/stdlib/Makefile
> index b3b30ab73e..f5755a1654 100644
> --- a/stdlib/Makefile
> +++ b/stdlib/Makefile
> @@ -81,7 +81,8 @@ tests := tst-strtol tst-strtod testmb testrand testsort testdiv \
> tst-width-stdint tst-strfrom tst-strfrom-locale \
> tst-getrandom tst-atexit tst-at_quick_exit \
> tst-cxa_atexit tst-on_exit test-atexit-race \
> - test-at_quick_exit-race test-cxa_atexit-race \
> + test-at_quick_exit-race test-cxa_atexit-race \
> + test-cxa_atexit-race2 \
> test-on_exit-race test-dlclose-exit-race \
> tst-makecontext-align test-bz22786 tst-strtod-nan-sign \
> tst-swapcontext1 tst-setcontext4 tst-setcontext5 \
> @@ -100,6 +101,7 @@ endif
> LDLIBS-test-atexit-race = $(shared-thread-library)
> LDLIBS-test-at_quick_exit-race = $(shared-thread-library)
> LDLIBS-test-cxa_atexit-race = $(shared-thread-library)
> +LDLIBS-test-cxa_atexit-race2 = $(shared-thread-library)
> LDLIBS-test-on_exit-race = $(shared-thread-library)
> LDLIBS-tst-canon-bz26341 = $(shared-thread-library)
>
> diff --git a/stdlib/exit.c b/stdlib/exit.c
> index bed82733ad..f095b38ab3 100644
> --- a/stdlib/exit.c
> +++ b/stdlib/exit.c
> @@ -45,6 +45,8 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
> if (run_dtors)
> __call_tls_dtors ();
>
> + __libc_lock_lock (__exit_funcs_lock);
> +
> /* We do it this way to handle recursive calls to exit () made by
> the functions registered with `atexit' and `on_exit'. We call
> everyone on the list and use the status value in the last
Ok, it avoids the second race condition.
> @@ -53,8 +55,6 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
> {
> struct exit_function_list *cur;
>
> - __libc_lock_lock (__exit_funcs_lock);
> -
> restart:
> cur = *listp;
>
I think there is no need use the goto anymore, since there is no need
to unlock the lock within the loop (the goto can be just a continue).
> @@ -63,7 +63,6 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
> /* Exit processing complete. We will not allow any more
> atexit/on_exit registrations. */
> __exit_funcs_done = true;
> - __libc_lock_unlock (__exit_funcs_lock);
> break;
> }
>
Ok, there is no need to unlock on break anymore.
> @@ -72,44 +71,52 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
> struct exit_function *const f = &cur->fns[--cur->idx];
> const uint64_t new_exitfn_called = __new_exitfn_called;
>
> - /* Unlock the list while we call a foreign function. */
> - __libc_lock_unlock (__exit_funcs_lock);
> switch (f->flavor)
> {
> void (*atfct) (void);
> void (*onfct) (int status, void *arg);
> void (*cxafct) (void *arg, int status);
> + void *arg;
>
> case ef_free:
> case ef_us:
> break;
> case ef_on:
> onfct = f->func.on.fn;
> + arg = f->func.on.arg;
> #ifdef PTR_DEMANGLE
> PTR_DEMANGLE (onfct);
> #endif
> - onfct (status, f->func.on.arg);
> + /* Unlock the list while we call a foreign function. */
> + __libc_lock_unlock (__exit_funcs_lock);
> + onfct (status, arg);
> + __libc_lock_lock (__exit_funcs_lock);
> break;
> case ef_at:
> atfct = f->func.at;
Ok.
> #ifdef PTR_DEMANGLE
> PTR_DEMANGLE (atfct);
> #endif
> + /* Unlock the list while we call a foreign function. */
> + __libc_lock_unlock (__exit_funcs_lock);
> atfct ();
> + __libc_lock_lock (__exit_funcs_lock);
> break;
Ok.
> case ef_cxa:
> /* To avoid dlclose/exit race calling cxafct twice (BZ 22180),
> we must mark this function as ef_free. */
> f->flavor = ef_free;
> cxafct = f->func.cxa.fn;
> + arg = f->func.cxa.arg;
> #ifdef PTR_DEMANGLE
> PTR_DEMANGLE (cxafct);
> #endif
> - cxafct (f->func.cxa.arg, status);
> + /* Unlock the list while we call a foreign function. */
> + __libc_lock_unlock (__exit_funcs_lock);
> + cxafct (arg, status);
> + __libc_lock_lock (__exit_funcs_lock);
> break;
> }
> - /* Re-lock again before looking at global state. */
> - __libc_lock_lock (__exit_funcs_lock);
>
> if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called))
> /* The last exit function, or another thread, has registered
Ok.
> @@ -123,9 +130,10 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
> allocate element. */
> free (cur);
>
> - __libc_lock_unlock (__exit_funcs_lock);
Just remove the extra newline below as well.
> }
>
> + __libc_lock_unlock (__exit_funcs_lock);
> +
> if (run_list_atexit)
> RUN_HOOK (__libc_atexit, ());
>
Ok.
> diff --git a/stdlib/test-cxa_atexit-race2.c b/stdlib/test-cxa_atexit-race2.c
> new file mode 100644
> index 0000000000..d8c3d418e7
> --- /dev/null
> +++ b/stdlib/test-cxa_atexit-race2.c
> @@ -0,0 +1,110 @@
> +/* Support file for atexit/exit, etc. race tests.
I think it would be good to add a reference to the bug report.
> + Copyright (C) 2017-2021 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/>. */
> +
> +/* This file must be run from within a directory called "stdlib". */
I don't think this true.
> +
> +/* The atexit/exit, at_quick_exit/quick_exit, __cxa_atexit/exit, etc. exhibited
> + data race while calling destructors.
> +
> + This test registers destructors from the background thread, and checks that
> + the same destructor is not called more than once. */
> +
> +#include <stdatomic.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <support/xthread.h>
> +#include <sys/wait.h>
> +#include <unistd.h>
> +
> +static atomic_int registered;
> +static atomic_int todo = 100000;
> +
> +static void
> +atexit_cb (void *arg)
> +{
> + atomic_fetch_sub (®istered, 1);
> + static void *prev;
> + if (arg == prev)
> + {
> + printf ("%p\n", arg);
> + abort ();
Use FAIL_EXIT1 here.
> + }
> + prev = arg;
> +
> + while (atomic_load (&todo) > 0 && atomic_load (®istered) < 100)
> + ;
> +}
> +
> +int __cxa_atexit (void (*func) (void *), void *arg, void *d);
> +
> +static void *
> +thread_func (void *arg)
> +{
> + void *cb_arg = NULL;
> + while (atomic_load (&todo) > 0)
Add a open bracket here.
> + if (atomic_load (®istered) < 10000)
> + {
> + int n = 10;
> + for (int i = 0; i < n; ++i)
> + __cxa_atexit (&atexit_cb, ++cb_arg, 0);
> + atomic_fetch_add (®istered, n);
> + atomic_fetch_sub (&todo, n);
> + }
> + return 0;
Use NULL here.
> +}
> +
> +static void
I would add a _Noreturn here.
> +test_and_exit (void)
> +{
> + pthread_attr_t attr;
> +
> + xpthread_attr_init (&attr);
> + xpthread_attr_setdetachstate (&attr, 1);
> +
> + xpthread_create (&attr, thread_func, NULL);
> + xpthread_attr_destroy (&attr);
> + while (!atomic_load (®istered))
Check for 0 here (unless the return value is a bool the type check
should be explicit).
> + ;
> + exit (0);
> +}
> +
> +static int
> +do_test (void)
> +{
> + for (int i = 0; i < 20; ++i)
> + {
> + for (int i = 0; i < 10; ++i)
> + if (fork () == 0)
Use xfork.
> + test_and_exit ();
> +
> + int status;
> + while (wait (&status) > 0)
> + {
> + if (!WIFEXITED (status))
I prefer if we limit the number of wait call to check for invalid
return codes:
for (int i = 0; i < 10; ++i)
{
int status;
xwaitpid (0, &status, 0);
if (!WIFEXITED (status))
FAIL_EXIT1 ("Failed iterations %d", i);
TEST_COMPARE (WEXITSTATUS (status), 0);
}
> + {
> + printf ("Failed interation %d\n", i);
> + abort ();
Use FAIL_EXIT1 here.
> + }
> + }
> + }
> +
> + exit (0);
There is no need to add an exit here.
> +}
> +
> +#define TEST_FUNCTION do_test
> +#include <support/test-driver.c>
>
Thank you. These improvements look good to me. Please push it.
On Thu, 13 May 2021 at 06:15, Adhemerval Zanella <
adhemerval.zanella@linaro.org> wrote:
>
>
> On 26/04/2021 16:27, Vitaly Buka via Libc-alpha wrote:
> > Fixes https://sourceware.org/bugzilla/show_bug.cgi?id=27749
> >
> > Keep __exit_funcs_lock almost all the time and unlock it only to execute
> > callbacks. This fixed two issues.
> >
> > 1. f->func.cxa was modified outside the lock with rare data race like:
> > thread 0: __run_exit_handlers unlock __exit_funcs_lock
> > thread 1: __internal_atexit locks __exit_funcs_lock
> > thread 0: f->flavor = ef_free;
> > thread 1: sees ef_free and use it as new
> > thread 1: new->func.cxa.fn = (void (*) (void *, int)) func;
> > thread 1: new->func.cxa.arg = arg;
> > thread 1: new->flavor = ef_cxa;
> > thread 0: cxafct = f->func.cxa.fn; // it's wrong fn!
> > thread 0: cxafct (f->func.cxa.arg, status); // it's wrong arg!
> > thread 0: goto restart;
> > thread 0: call the same exit_function again as it's ef_cxa
>
> Ok, the small window between fetching the function pointer and argument
> from the list is triggering a race condition.
>
> >
> > 2. Don't unlock in main while loop after *listp = cur->next. If *listp
> > is NULL and __exit_funcs_done is false another thread may fail in
> > __new_exitfn on assert (l != NULL):
> > thread 0: *listp = cur->next; // It can be the last: *listp =
> NULL.
> > thread 0: __libc_lock_unlock
> > thread 1: __libc_lock_lock in __on_exit
> > thread 1: __new_exitfn
> > thread 1: if (__exit_funcs_done) // false: thread 0 isn't there
> yet.
> > thread 1: l = *listp
> > thread 1: moves one and crashes on assert (l != NULL);
>
> Yeah, this is tricky but it does look correct. I guess the lock/unlock
> during the loop was added to give a chance to concurrent
> __cxa_atexit / on_exit to have a chance to add a new callback, but it
> also only complicates things as you noted. We might try to fix it on the
> __new_exitfn (to avoid the assert), but I see the current approach of
> locking the list and only unlocking while running the callback is the
> right approach.
>
> The patch look ok in general, I added some comments below. I have
> adjusted the patch based on my comments [1], if you are ok with them
> I can push it upstream.
>
> [1]
> https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/azanella/bz27749-atexit-fix
>
> >
> > The test needs multiple iterations to consistently fail without the fix.
> > ---
> > stdlib/Makefile | 4 +-
> > stdlib/exit.c | 28 ++++++---
> > stdlib/test-cxa_atexit-race2.c | 110 +++++++++++++++++++++++++++++++++
> > 3 files changed, 131 insertions(+), 11 deletions(-)
> > create mode 100644 stdlib/test-cxa_atexit-race2.c
> >
> > diff --git a/stdlib/Makefile b/stdlib/Makefile
> > index b3b30ab73e..f5755a1654 100644
> > --- a/stdlib/Makefile
> > +++ b/stdlib/Makefile
> > @@ -81,7 +81,8 @@ tests := tst-strtol tst-strtod testmb
> testrand testsort testdiv \
> > tst-width-stdint tst-strfrom tst-strfrom-locale
> \
> > tst-getrandom tst-atexit tst-at_quick_exit
> \
> > tst-cxa_atexit tst-on_exit test-atexit-race
> \
> > - test-at_quick_exit-race test-cxa_atexit-race
> \
> > + test-at_quick_exit-race test-cxa_atexit-race
> \
> > + test-cxa_atexit-race2
> \
> > test-on_exit-race test-dlclose-exit-race
> \
> > tst-makecontext-align test-bz22786 tst-strtod-nan-sign \
> > tst-swapcontext1 tst-setcontext4 tst-setcontext5 \
> > @@ -100,6 +101,7 @@ endif
> > LDLIBS-test-atexit-race = $(shared-thread-library)
> > LDLIBS-test-at_quick_exit-race = $(shared-thread-library)
> > LDLIBS-test-cxa_atexit-race = $(shared-thread-library)
> > +LDLIBS-test-cxa_atexit-race2 = $(shared-thread-library)
> > LDLIBS-test-on_exit-race = $(shared-thread-library)
> > LDLIBS-tst-canon-bz26341 = $(shared-thread-library)
> >
> > diff --git a/stdlib/exit.c b/stdlib/exit.c
> > index bed82733ad..f095b38ab3 100644
> > --- a/stdlib/exit.c
> > +++ b/stdlib/exit.c
> > @@ -45,6 +45,8 @@ __run_exit_handlers (int status, struct
> exit_function_list **listp,
> > if (run_dtors)
> > __call_tls_dtors ();
> >
> > + __libc_lock_lock (__exit_funcs_lock);
> > +
> > /* We do it this way to handle recursive calls to exit () made by
> > the functions registered with `atexit' and `on_exit'. We call
> > everyone on the list and use the status value in the last
>
> Ok, it avoids the second race condition.
>
> > @@ -53,8 +55,6 @@ __run_exit_handlers (int status, struct
> exit_function_list **listp,
> > {
> > struct exit_function_list *cur;
> >
> > - __libc_lock_lock (__exit_funcs_lock);
> > -
> > restart:
> > cur = *listp;
> >
>
> I think there is no need use the goto anymore, since there is no need
> to unlock the lock within the loop (the goto can be just a continue).
>
> > @@ -63,7 +63,6 @@ __run_exit_handlers (int status, struct
> exit_function_list **listp,
> > /* Exit processing complete. We will not allow any more
> > atexit/on_exit registrations. */
> > __exit_funcs_done = true;
> > - __libc_lock_unlock (__exit_funcs_lock);
> > break;
> > }
> >
>
> Ok, there is no need to unlock on break anymore.
>
> > @@ -72,44 +71,52 @@ __run_exit_handlers (int status, struct
> exit_function_list **listp,
> > struct exit_function *const f = &cur->fns[--cur->idx];
> > const uint64_t new_exitfn_called = __new_exitfn_called;
> >
> > - /* Unlock the list while we call a foreign function. */
> > - __libc_lock_unlock (__exit_funcs_lock);
> > switch (f->flavor)
> > {
> > void (*atfct) (void);
> > void (*onfct) (int status, void *arg);
> > void (*cxafct) (void *arg, int status);
> > + void *arg;
> >
> > case ef_free:
> > case ef_us:
> > break;
> > case ef_on:
> > onfct = f->func.on.fn;
> > + arg = f->func.on.arg;
> > #ifdef PTR_DEMANGLE
> > PTR_DEMANGLE (onfct);
> > #endif
> > - onfct (status, f->func.on.arg);
> > + /* Unlock the list while we call a foreign function. */
> > + __libc_lock_unlock (__exit_funcs_lock);
> > + onfct (status, arg);
> > + __libc_lock_lock (__exit_funcs_lock);
> > break;
> > case ef_at:
> > atfct = f->func.at;
>
> Ok.
>
> > #ifdef PTR_DEMANGLE
> > PTR_DEMANGLE (atfct);
> > #endif
> > + /* Unlock the list while we call a foreign function. */
> > + __libc_lock_unlock (__exit_funcs_lock);
> > atfct ();
> > + __libc_lock_lock (__exit_funcs_lock);
> > break;
>
> Ok.
>
> > case ef_cxa:
> > /* To avoid dlclose/exit race calling cxafct twice (BZ
> 22180),
> > we must mark this function as ef_free. */
> > f->flavor = ef_free;
> > cxafct = f->func.cxa.fn;
> > + arg = f->func.cxa.arg;
> > #ifdef PTR_DEMANGLE
> > PTR_DEMANGLE (cxafct);
> > #endif
> > - cxafct (f->func.cxa.arg, status);
> > + /* Unlock the list while we call a foreign function. */
> > + __libc_lock_unlock (__exit_funcs_lock);
> > + cxafct (arg, status);
> > + __libc_lock_lock (__exit_funcs_lock);
> > break;
> > }
> > - /* Re-lock again before looking at global state. */
> > - __libc_lock_lock (__exit_funcs_lock);
> >
> > if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called))
> > /* The last exit function, or another thread, has registered
>
> Ok.
>
> > @@ -123,9 +130,10 @@ __run_exit_handlers (int status, struct
> exit_function_list **listp,
> > allocate element. */
> > free (cur);
> >
> > - __libc_lock_unlock (__exit_funcs_lock);
>
> Just remove the extra newline below as well.
>
> > }
> >
> > + __libc_lock_unlock (__exit_funcs_lock);
> > +
> > if (run_list_atexit)
> > RUN_HOOK (__libc_atexit, ());
> >
>
> Ok.
>
> > diff --git a/stdlib/test-cxa_atexit-race2.c
> b/stdlib/test-cxa_atexit-race2.c
> > new file mode 100644
> > index 0000000000..d8c3d418e7
> > --- /dev/null
> > +++ b/stdlib/test-cxa_atexit-race2.c
> > @@ -0,0 +1,110 @@
> > +/* Support file for atexit/exit, etc. race tests.
>
> I think it would be good to add a reference to the bug report.
>
> > + Copyright (C) 2017-2021 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/>. */
> > +
> > +/* This file must be run from within a directory called "stdlib". */
>
> I don't think this true.
>
> > +
> > +/* The atexit/exit, at_quick_exit/quick_exit, __cxa_atexit/exit, etc.
> exhibited
> > + data race while calling destructors.
> > +
> > + This test registers destructors from the background thread, and
> checks that
> > + the same destructor is not called more than once. */
> > +
> > +#include <stdatomic.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <support/xthread.h>
> > +#include <sys/wait.h>
> > +#include <unistd.h>
> > +
> > +static atomic_int registered;
> > +static atomic_int todo = 100000;
> > +
> > +static void
> > +atexit_cb (void *arg)
> > +{
> > + atomic_fetch_sub (®istered, 1);
> > + static void *prev;
> > + if (arg == prev)
> > + {
> > + printf ("%p\n", arg);
> > + abort ();
>
> Use FAIL_EXIT1 here.
>
> > + }
> > + prev = arg;
> > +
> > + while (atomic_load (&todo) > 0 && atomic_load (®istered) < 100)
> > + ;
> > +}
> > +
> > +int __cxa_atexit (void (*func) (void *), void *arg, void *d);
> > +
> > +static void *
> > +thread_func (void *arg)
> > +{
> > + void *cb_arg = NULL;
> > + while (atomic_load (&todo) > 0)
>
> Add a open bracket here.
>
> > + if (atomic_load (®istered) < 10000)
> > + {
> > + int n = 10;
> > + for (int i = 0; i < n; ++i)
> > + __cxa_atexit (&atexit_cb, ++cb_arg, 0);
> > + atomic_fetch_add (®istered, n);
> > + atomic_fetch_sub (&todo, n);
> > + }
> > + return 0;
>
> Use NULL here.
>
> > +}
> > +
> > +static void
>
> I would add a _Noreturn here.
>
> > +test_and_exit (void)
> > +{
> > + pthread_attr_t attr;
> > +
> > + xpthread_attr_init (&attr);
> > + xpthread_attr_setdetachstate (&attr, 1);
> > +
> > + xpthread_create (&attr, thread_func, NULL);
> > + xpthread_attr_destroy (&attr);
> > + while (!atomic_load (®istered))
>
> Check for 0 here (unless the return value is a bool the type check
> should be explicit).
>
> > + ;
> > + exit (0);
> > +}
> > +
> > +static int
> > +do_test (void)
> > +{
> > + for (int i = 0; i < 20; ++i)
> > + {
> > + for (int i = 0; i < 10; ++i)
> > + if (fork () == 0)
>
> Use xfork.
>
> > + test_and_exit ();
> > +
> > + int status;
> > + while (wait (&status) > 0)
> > + {
> > + if (!WIFEXITED (status))
>
> I prefer if we limit the number of wait call to check for invalid
> return codes:
>
> for (int i = 0; i < 10; ++i)
> {
> int status;
> xwaitpid (0, &status, 0);
> if (!WIFEXITED (status))
> FAIL_EXIT1 ("Failed iterations %d", i);
> TEST_COMPARE (WEXITSTATUS (status), 0);
> }
>
> > + {
> > + printf ("Failed interation %d\n", i);
> > + abort ();
>
> Use FAIL_EXIT1 here.
>
> > + }
> > + }
> > + }
> > +
> > + exit (0);
>
> There is no need to add an exit here.
>
> > +}
> > +
> > +#define TEST_FUNCTION do_test
> > +#include <support/test-driver.c>
> >
>
@@ -81,7 +81,8 @@ tests := tst-strtol tst-strtod testmb testrand testsort testdiv \
tst-width-stdint tst-strfrom tst-strfrom-locale \
tst-getrandom tst-atexit tst-at_quick_exit \
tst-cxa_atexit tst-on_exit test-atexit-race \
- test-at_quick_exit-race test-cxa_atexit-race \
+ test-at_quick_exit-race test-cxa_atexit-race \
+ test-cxa_atexit-race2 \
test-on_exit-race test-dlclose-exit-race \
tst-makecontext-align test-bz22786 tst-strtod-nan-sign \
tst-swapcontext1 tst-setcontext4 tst-setcontext5 \
@@ -100,6 +101,7 @@ endif
LDLIBS-test-atexit-race = $(shared-thread-library)
LDLIBS-test-at_quick_exit-race = $(shared-thread-library)
LDLIBS-test-cxa_atexit-race = $(shared-thread-library)
+LDLIBS-test-cxa_atexit-race2 = $(shared-thread-library)
LDLIBS-test-on_exit-race = $(shared-thread-library)
LDLIBS-tst-canon-bz26341 = $(shared-thread-library)
@@ -45,6 +45,8 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
if (run_dtors)
__call_tls_dtors ();
+ __libc_lock_lock (__exit_funcs_lock);
+
/* We do it this way to handle recursive calls to exit () made by
the functions registered with `atexit' and `on_exit'. We call
everyone on the list and use the status value in the last
@@ -53,8 +55,6 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
{
struct exit_function_list *cur;
- __libc_lock_lock (__exit_funcs_lock);
-
restart:
cur = *listp;
@@ -63,7 +63,6 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
/* Exit processing complete. We will not allow any more
atexit/on_exit registrations. */
__exit_funcs_done = true;
- __libc_lock_unlock (__exit_funcs_lock);
break;
}
@@ -72,44 +71,52 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
struct exit_function *const f = &cur->fns[--cur->idx];
const uint64_t new_exitfn_called = __new_exitfn_called;
- /* Unlock the list while we call a foreign function. */
- __libc_lock_unlock (__exit_funcs_lock);
switch (f->flavor)
{
void (*atfct) (void);
void (*onfct) (int status, void *arg);
void (*cxafct) (void *arg, int status);
+ void *arg;
case ef_free:
case ef_us:
break;
case ef_on:
onfct = f->func.on.fn;
+ arg = f->func.on.arg;
#ifdef PTR_DEMANGLE
PTR_DEMANGLE (onfct);
#endif
- onfct (status, f->func.on.arg);
+ /* Unlock the list while we call a foreign function. */
+ __libc_lock_unlock (__exit_funcs_lock);
+ onfct (status, arg);
+ __libc_lock_lock (__exit_funcs_lock);
break;
case ef_at:
atfct = f->func.at;
#ifdef PTR_DEMANGLE
PTR_DEMANGLE (atfct);
#endif
+ /* Unlock the list while we call a foreign function. */
+ __libc_lock_unlock (__exit_funcs_lock);
atfct ();
+ __libc_lock_lock (__exit_funcs_lock);
break;
case ef_cxa:
/* To avoid dlclose/exit race calling cxafct twice (BZ 22180),
we must mark this function as ef_free. */
f->flavor = ef_free;
cxafct = f->func.cxa.fn;
+ arg = f->func.cxa.arg;
#ifdef PTR_DEMANGLE
PTR_DEMANGLE (cxafct);
#endif
- cxafct (f->func.cxa.arg, status);
+ /* Unlock the list while we call a foreign function. */
+ __libc_lock_unlock (__exit_funcs_lock);
+ cxafct (arg, status);
+ __libc_lock_lock (__exit_funcs_lock);
break;
}
- /* Re-lock again before looking at global state. */
- __libc_lock_lock (__exit_funcs_lock);
if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called))
/* The last exit function, or another thread, has registered
@@ -123,9 +130,10 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
allocate element. */
free (cur);
- __libc_lock_unlock (__exit_funcs_lock);
}
+ __libc_lock_unlock (__exit_funcs_lock);
+
if (run_list_atexit)
RUN_HOOK (__libc_atexit, ());
new file mode 100644
@@ -0,0 +1,110 @@
+/* Support file for atexit/exit, etc. race tests.
+ Copyright (C) 2017-2021 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/>. */
+
+/* This file must be run from within a directory called "stdlib". */
+
+/* The atexit/exit, at_quick_exit/quick_exit, __cxa_atexit/exit, etc. exhibited
+ data race while calling destructors.
+
+ This test registers destructors from the background thread, and checks that
+ the same destructor is not called more than once. */
+
+#include <stdatomic.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/xthread.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+static atomic_int registered;
+static atomic_int todo = 100000;
+
+static void
+atexit_cb (void *arg)
+{
+ atomic_fetch_sub (®istered, 1);
+ static void *prev;
+ if (arg == prev)
+ {
+ printf ("%p\n", arg);
+ abort ();
+ }
+ prev = arg;
+
+ while (atomic_load (&todo) > 0 && atomic_load (®istered) < 100)
+ ;
+}
+
+int __cxa_atexit (void (*func) (void *), void *arg, void *d);
+
+static void *
+thread_func (void *arg)
+{
+ void *cb_arg = NULL;
+ while (atomic_load (&todo) > 0)
+ if (atomic_load (®istered) < 10000)
+ {
+ int n = 10;
+ for (int i = 0; i < n; ++i)
+ __cxa_atexit (&atexit_cb, ++cb_arg, 0);
+ atomic_fetch_add (®istered, n);
+ atomic_fetch_sub (&todo, n);
+ }
+ return 0;
+}
+
+static void
+test_and_exit (void)
+{
+ pthread_attr_t attr;
+
+ xpthread_attr_init (&attr);
+ xpthread_attr_setdetachstate (&attr, 1);
+
+ xpthread_create (&attr, thread_func, NULL);
+ xpthread_attr_destroy (&attr);
+ while (!atomic_load (®istered))
+ ;
+ exit (0);
+}
+
+static int
+do_test (void)
+{
+ for (int i = 0; i < 20; ++i)
+ {
+ for (int i = 0; i < 10; ++i)
+ if (fork () == 0)
+ test_and_exit ();
+
+ int status;
+ while (wait (&status) > 0)
+ {
+ if (!WIFEXITED (status))
+ {
+ printf ("Failed interation %d\n", i);
+ abort ();
+ }
+ }
+ }
+
+ exit (0);
+}
+
+#define TEST_FUNCTION do_test
+#include <support/test-driver.c>