Re: [PATCH v4] elf: Avoid deadlock between pthread_create and ctors [BZ #28357]

[Andreas Schwab <schwab@linux-m68k.org>]

On Feb 02 2022, Szabolcs Nagy wrote:

> The 02/02/2022 15:31, Andreas Schwab wrote:
>> On Okt 01 2021, Szabolcs Nagy via Libc-alpha wrote:
>> 
>> > diff --git a/elf/dl-open.c b/elf/dl-open.c
>> > index 5295e931b0..6ea5dd2457 100644
>> > --- a/elf/dl-open.c
>> > +++ b/elf/dl-open.c
>> > @@ -66,6 +66,9 @@ struct dl_open_args
>> >       libc_map value in the namespace in case of a dlopen failure.  */
>> >    bool libc_already_loaded;
>> >  
>> > +  /* Set to true if the end of dl_open_worker_begin was reached.  */
>> > +  bool worker_continue;
>> > +
>> >    /* Original parameters to the program and the current environment.  */
>> >    int argc;
>> >    char **argv;
>> > @@ -482,7 +485,7 @@ call_dl_init (void *closure)
>> >  }
>> >  
>> >  static void
>> > -dl_open_worker (void *a)
>> > +dl_open_worker_begin (void *a)
>> >  {
>> >    struct dl_open_args *args = a;
>> >    const char *file = args->file;
>> > @@ -774,6 +777,36 @@ dl_open_worker (void *a)
>> >        _dl_call_libc_early_init (libc_map, false);
>> >      }
>> >  
>> > +  args->worker_continue = true;
>> > +}
>> > +
>> > +static void
>> > +dl_open_worker (void *a)
>> > +{
>> > +  struct dl_open_args *args = a;
>> > +
>> > +  args->worker_continue = false;
>> > +
>> > +  {
>> > +    /* Protects global and module specific TLS state.  */
>> > +    __rtld_lock_lock_recursive (GL(dl_load_tls_lock));
>> > +
>> > +    struct dl_exception ex;
>> > +    int err = _dl_catch_exception (&ex, dl_open_worker_begin, args);
>> > +
>> > +    __rtld_lock_unlock_recursive (GL(dl_load_tls_lock));
>> > +
>> > +    if (__glibc_unlikely (ex.errstring != NULL))
>> > +      /* Reraise the error.  */
>> > +      _dl_signal_exception (err, &ex, NULL);
>> > +  }
>> > +
>> > +  if (!args->worker_continue)
>> > +    return;
>> 
>> Why do you need worker_continue?  How can worker_continue not be set at
>> this point?
>
> because dl_open_worker_begin (old dl_open_worker) can simply return.

And what does dl_open_worker_begin do as its very last thing?

-- 
Andreas Schwab, schwab@linux-m68k.org
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