On Tue, Dec 29, 2020 at 12:46:54PM +0100, Mark Kettenis wrote:
> > Date: Tue, 29 Dec 2020 12:21:25 +0100
> > From: Otto Moerbeek <[email protected]>
> >
> > Hi,
> >
> > this is a continuation from the threads on bugs@
> >
> > This version makes it explicit to *only* setup "TLS" (which actually
> > is just a pointer to static data) with the data provided if we're
> > running single threaded (ie.. no -pthread or -pthread but no pthread
> > function that triggers multi-threaded init called yet). In all other
> > cases the real allocated TLS is zero'ed. This avoids the setup issue
> > asr is having. This diff also makes sure asr uses a specialized
> > destructor for it's TLS to kill a mem leak that occurs on thread
> > destruction.
> >
> > All in all I'm still a bit fond of the constructor approach to
> > librthread init: it makes the distinction between having a single
> > thread and being the main thread in a multi-threaded setup moot.
> >
> > Anyway, we can consider that later, please test this.
>
> This isn't right. The memcpy() call you're removing is there such
> that the contents of the per-thread storage for the initial (main)
> thread remains the same.
>
> With your change it reverts back to zero when the first thread is
> created. In the particular case at hand that means the initial thread
> would get a fresh resolver context at that point.
Yes, but if I do not that crashes happen on destruct. Note that your
initial suggestion (in asr.c)
if (priv != &_asr && *priv == _asr)
*priv = NULL;
has the same property: it clears the contents if they happen to be the
same as _asr.
The crash happens if the pre-mt (static) and the TLS of the main
thread share the same data. I did not find a way to make that work, so
I decided to use the big hammer. I might be overlooking something
obvious though...
-Otto
>
> > Index: asr/asr.c
> > ===================================================================
> > RCS file: /cvs/src/lib/libc/asr/asr.c,v
> > retrieving revision 1.64
> > diff -u -p -r1.64 asr.c
> > --- asr/asr.c 6 Jul 2020 13:33:05 -0000 1.64
> > +++ asr/asr.c 29 Dec 2020 11:10:08 -0000
> > @@ -117,7 +117,7 @@ _asr_resolver_done(void *arg)
> > _asr_ctx_unref(ac);
> > return;
> > } else {
> > - priv = _THREAD_PRIVATE(_asr, _asr, &_asr);
> > + priv = _THREAD_PRIVATE_DT(_asr, _asr, NULL, &_asr);
> > if (*priv == NULL)
> > return;
> > asr = *priv;
> > @@ -128,6 +128,21 @@ _asr_resolver_done(void *arg)
> > free(asr);
> > }
> >
> > +static void
> > +_asr_resolver_done_tp(void *arg)
> > +{
> > + struct asr **priv = arg;
> > + struct asr *asr;
> > +
> > + if (*priv == NULL)
> > + return;
> > + asr = *priv;
> > +
> > + _asr_ctx_unref(asr->a_ctx);
> > + free(asr);
> > + free(priv);
> > +}
> > +
> > void *
> > asr_resolver_from_string(const char *str)
> > {
> > @@ -349,7 +364,8 @@ _asr_use_resolver(void *arg)
> > }
> > else {
> > DPRINT("using thread-local resolver\n");
> > - priv = _THREAD_PRIVATE(_asr, _asr, &_asr);
> > + priv = _THREAD_PRIVATE_DT(_asr, _asr, _asr_resolver_done_tp,
> > + &_asr);
> > if (*priv == NULL) {
> > DPRINT("setting up thread-local resolver\n");
> > *priv = _asr_resolver();
> > Index: include/thread_private.h
> > ===================================================================
> > RCS file: /cvs/src/lib/libc/include/thread_private.h,v
> > retrieving revision 1.35
> > diff -u -p -r1.35 thread_private.h
> > --- include/thread_private.h 13 Feb 2019 13:22:14 -0000 1.35
> > +++ include/thread_private.h 29 Dec 2020 11:10:08 -0000
> > @@ -51,7 +51,7 @@ PROTO_NORMAL(_malloc_init);
> > * tc_tag_storage:
> > * Returns a pointer to per-thread instance of data associated
> > * with the given tag. If the given tag is NULL a tag is
> > - * allocated and initialized automatically.
> > + * allocated and cleared automatically.
> > *
> > * tc_fork, tc_vfork:
> > * If not NULL, they are called instead of the syscall stub, so that
> > @@ -98,7 +98,7 @@ struct thread_callbacks {
> > void (*tc_mutex_destroy)(void **);
> > void (*tc_tag_lock)(void **);
> > void (*tc_tag_unlock)(void **);
> > - void *(*tc_tag_storage)(void **, void *, size_t, void *);
> > + void *(*tc_tag_storage)(void **, size_t, void (*)(void *), void *);
> > __pid_t (*tc_fork)(void);
> > __pid_t (*tc_vfork)(void);
> > void (*tc_thread_release)(struct pthread *);
> > @@ -142,6 +142,7 @@ __END_HIDDEN_DECLS
> > #define _THREAD_PRIVATE_MUTEX_LOCK(name) do {} while (0)
> > #define _THREAD_PRIVATE_MUTEX_UNLOCK(name) do {} while (0)
> > #define _THREAD_PRIVATE(keyname, storage, error) &(storage)
> > +#define _THREAD_PRIVATE_DT(keyname, storage, dt, error) &(storage)
> > #define _MUTEX_LOCK(mutex) do {} while (0)
> > #define _MUTEX_UNLOCK(mutex) do {} while (0)
> > #define _MUTEX_DESTROY(mutex) do {} while (0)
> > @@ -168,7 +169,12 @@ __END_HIDDEN_DECLS
> > #define _THREAD_PRIVATE(keyname, storage, error) \
> > (_thread_cb.tc_tag_storage == NULL ? &(storage) : \
> > _thread_cb.tc_tag_storage(&(__THREAD_NAME(keyname)), \
> > - &(storage), sizeof(storage), error))
> > + sizeof(storage), NULL, (error)))
> > +
> > +#define _THREAD_PRIVATE_DT(keyname, storage, dt, error)
> > \
> > + (_thread_cb.tc_tag_storage == NULL ? &(storage) : \
> > + _thread_cb.tc_tag_storage(&(__THREAD_NAME(keyname)), \
> > + sizeof(storage), (dt), (error)))
> >
> > /*
> > * Macros used in libc to access mutexes.
> > Index: thread/rthread_cb.h
> > ===================================================================
> > RCS file: /cvs/src/lib/libc/thread/rthread_cb.h,v
> > retrieving revision 1.2
> > diff -u -p -r1.2 rthread_cb.h
> > --- thread/rthread_cb.h 5 Sep 2017 02:40:54 -0000 1.2
> > +++ thread/rthread_cb.h 29 Dec 2020 11:10:08 -0000
> > @@ -35,5 +35,5 @@ void _thread_mutex_unlock(void **);
> > void _thread_mutex_destroy(void **);
> > void _thread_tag_lock(void **);
> > void _thread_tag_unlock(void **);
> > -void *_thread_tag_storage(void **, void *, size_t, void *);
> > +void *_thread_tag_storage(void **, size_t, void (*)(void*), void *);
> > __END_HIDDEN_DECLS
> > Index: thread/rthread_libc.c
> > ===================================================================
> > RCS file: /cvs/src/lib/libc/thread/rthread_libc.c,v
> > retrieving revision 1.3
> > diff -u -p -r1.3 rthread_libc.c
> > --- thread/rthread_libc.c 10 Jan 2019 18:45:33 -0000 1.3
> > +++ thread/rthread_libc.c 29 Dec 2020 11:10:08 -0000
> > @@ -31,7 +31,7 @@ static pthread_mutex_t _thread_tag_mutex
> > * This function will never return NULL.
> > */
> > static void
> > -_thread_tag_init(void **tag)
> > +_thread_tag_init(void **tag, void (*dt)(void *))
> > {
> > struct _thread_tag *tt;
> > int result;
> > @@ -42,7 +42,8 @@ _thread_tag_init(void **tag)
> > tt = malloc(sizeof *tt);
> > if (tt != NULL) {
> > result = pthread_mutex_init(&tt->m, NULL);
> > - result |= pthread_key_create(&tt->k, free);
> > + result |= pthread_key_create(&tt->k, dt ? dt :
> > + free);
> > *tag = tt;
> > }
> > }
> > @@ -62,7 +63,7 @@ _thread_tag_lock(void **tag)
> >
> > if (__isthreaded) {
> > if (*tag == NULL)
> > - _thread_tag_init(tag);
> > + _thread_tag_init(tag, NULL);
> > tt = *tag;
> > if (pthread_mutex_lock(&tt->m) != 0)
> > _rthread_debug(1, "tag mutex lock failure");
> > @@ -79,7 +80,7 @@ _thread_tag_unlock(void **tag)
> >
> > if (__isthreaded) {
> > if (*tag == NULL)
> > - _thread_tag_init(tag);
> > + _thread_tag_init(tag, NULL);
> > tt = *tag;
> > if (pthread_mutex_unlock(&tt->m) != 0)
> > _rthread_debug(1, "tag mutex unlock failure");
> > @@ -88,28 +89,26 @@ _thread_tag_unlock(void **tag)
> >
> > /*
> > * return the thread specific data for the given tag. If there
> > - * is no data for this thread initialize it from 'storage'.
> > + * is no data for this thread allocate and clear it.
> > * On any error return 'err'.
> > */
> > void *
> > -_thread_tag_storage(void **tag, void *storage, size_t sz, void *err)
> > +_thread_tag_storage(void **tag, size_t sz, void (*dt)(void *), void *err)
> > {
> > struct _thread_tag *tt;
> > void *ret;
> >
> > if (*tag == NULL)
> > - _thread_tag_init(tag);
> > + _thread_tag_init(tag, dt);
> > tt = *tag;
> >
> > ret = pthread_getspecific(tt->k);
> > if (ret == NULL) {
> > - ret = malloc(sz);
> > + ret = calloc(1, sz);
> > if (ret == NULL)
> > ret = err;
> > else {
> > - if (pthread_setspecific(tt->k, ret) == 0)
> > - memcpy(ret, storage, sz);
> > - else {
> > + if (pthread_setspecific(tt->k, ret) != 0) {
> > free(ret);
> > ret = err;
> > }
> >
> >
