Message ID | 20210426192036.1743585-1-vitalybuka@google.com |
---|---|
State | New |
Headers | show |
Series | stdlib: Fix data race in __run_exit_handlers | expand |
The last patch removes static cb_arg and improves description of race case 2. On Mon, 26 Apr 2021 at 12:20, Vitaly Buka <vitalybuka@google.com> 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 > > 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 | 109 +++++++++++++++++++++++++++++++++ > 3 files changed, 130 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 > @@ -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, ()); > > diff --git a/stdlib/test-cxa_atexit-race2.c > b/stdlib/test-cxa_atexit-race2.c > new file mode 100644 > index 0000000000..9ab110ebaf > --- /dev/null > +++ b/stdlib/test-cxa_atexit-race2.c > @@ -0,0 +1,109 @@ > +/* 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> > -- > 2.31.1.498.g6c1eba8ee3d-goog > >
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 @@ -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, ()); diff --git a/stdlib/test-cxa_atexit-race2.c b/stdlib/test-cxa_atexit-race2.c new file mode 100644 index 0000000000..9ab110ebaf --- /dev/null +++ b/stdlib/test-cxa_atexit-race2.c @@ -0,0 +1,109 @@ +/* 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>