Date: Wed, 22 Mar 2006 19:43:12 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Kazuaki Oda <kaakun@highway.ne.jp> Cc: kan@freebsd.org, hackers@freebsd.org Subject: Re: dlopen() and dlclose() are not MT-safe? Message-ID: <20060322174312.GB27116@deviant.kiev.zoral.com.ua> In-Reply-To: <44215FE9.2070602@highway.ne.jp> References: <44215FE9.2070602@highway.ne.jp>
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On Wed, Mar 22, 2006 at 11:32:09PM +0900, Kazuaki Oda wrote:
> Hello,
>=20
> I compiled the following code on 6.1-PRERELEASE and ran:
>=20
> dltest.c
> ----------------------------------------------------------------------
> #include <err.h>
> #include <dlfcn.h>
> #include <pthread.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
>=20
> #define NTHREADS 10
>=20
> void *func(void *dummy);
>=20
> int main(void)
> {
> pthread_t tids[NTHREADS];
> int error;
> int i;
>=20
> for (i =3D 0; i < NTHREADS; i++) {
> error =3D pthread_create(&tids[i], NULL, func, NULL);
> if (error)
> errc(1, error, "pthread_create");
> }
>=20
> for (;;)
> sleep(1);
>=20
> /* NOTREACHED */
>=20
> exit(0);
> }
>=20
> void *func(void *dummy)
> {
> void *h;
>=20
> for (;;) {
> if ((h =3D dlopen("/usr/lib/libm.so", RTLD_NOW)) =3D=3D NULL)
> errx(1, "dlopen: %s", dlerror());
> if (dlclose(h) =3D=3D -1)
> errx(1, "dlclose: %s", dlerror());
> }
>=20
> /* NOTREACHED */
>=20
> return (NULL);
> }
> ----------------------------------------------------------------------
>=20
> % cc -Wall -o dltest dltest.c -lpthread
> % ./dltest
> ld-elf.so.1: assert failed: /usr/src/libexec/rtld-elf/rtld.c:2445
> Segmentation fault (core dumped)
>=20
> % cc -Wall -o dltest dltest.c -lthr
> % ./dltest
> % ld-elf.so.1: assert failed: /usr/src/libexec/rtld-elf/rtld.c:1723
> Abort (core dumped)
>=20
> Hmm, it seems dlopen() and dlclose() are not MT-safe. Is this a known
> issue?
>=20
> --
> Kazuaki Oda
The following patch put some relief for the problem:
Index: libexec/rtld-elf/rtld.c =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /usr/local/arch/ncvs/src/libexec/rtld-elf/rtld.c,v
retrieving revision 1.112
diff -u -r1.112 rtld.c
--- libexec/rtld-elf/rtld.c 24 Dec 2005 15:37:30 -0000 1.112
+++ libexec/rtld-elf/rtld.c 22 Mar 2006 17:33:06 -0000
@@ -1688,6 +1688,12 @@
wlock_release(rtld_bind_lock, lockstate);
objlist_call_fini(&list_fini);
lockstate =3D wlock_acquire(rtld_bind_lock);
+ if (root->refcount =3D=3D 0) {
+ _rtld_error("%s: object busy", root->path);
+ wlock_release(rtld_bind_lock, lockstate);
+ return -1;
+ }
+
objlist_remove_unref(&list_fini);
/* Finish cleaning up the newly-unreferenced objects. */
But it still allows for the mess of _init/_fini simultaneous calls
from different threads. SUSv3 does not mention constructors/destructors.
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