| Message ID | f8ea2b9982e39fd950d157f5dba31121ceb51df3.1618301209.git.szabolcs.nagy@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | Dynamic TLS related data race fixes | expand |
On 13/04/2021 05:21, Szabolcs Nagy via Libc-alpha wrote: > Remove generic tlsdesc code related to lazy tlsdesc processing since > lazy tlsdesc relocation is no longer supported. This includes removing > GL(dl_load_lock) from _dl_make_tlsdesc_dynamic which is only called at > load time when that lock is already held. > > Added a documentation comment too. LGTM, thanks. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> > --- > elf/tlsdeschtab.h | 53 +++++---------------------------------- > sysdeps/aarch64/tlsdesc.c | 1 - > sysdeps/arm/tlsdesc.c | 1 - > sysdeps/i386/tlsdesc.c | 1 - > sysdeps/x86_64/tlsdesc.c | 1 - > 5 files changed, 6 insertions(+), 51 deletions(-) > > diff --git a/elf/tlsdeschtab.h b/elf/tlsdeschtab.h > index 21695fd1e9..85bd0415e1 100644 > --- a/elf/tlsdeschtab.h > +++ b/elf/tlsdeschtab.h > @@ -78,6 +78,10 @@ map_generation (struct link_map *map) > return GL(dl_tls_generation) + 1; > } > > +/* Returns the data pointer for a given map and tls offset that is used > + to fill in one of the GOT entries referenced by a TLSDESC relocation > + when using dynamic TLS. This requires allocation, returns NULL on > + allocation failure. */ > void * > _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset) > { > @@ -85,18 +89,12 @@ _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset) > void **entry; > struct tlsdesc_dynamic_arg *td, test; > > - /* FIXME: We could use a per-map lock here, but is it worth it? */ > - __rtld_lock_lock_recursive (GL(dl_load_lock)); > - > ht = map->l_mach.tlsdesc_table; > if (! ht) > { > ht = htab_create (); > if (! ht) > - { > - __rtld_lock_unlock_recursive (GL(dl_load_lock)); > - return 0; > - } > + return 0; > map->l_mach.tlsdesc_table = ht; > } > Ok. > @@ -104,15 +102,11 @@ _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset) > test.tlsinfo.ti_offset = ti_offset; > entry = htab_find_slot (ht, &test, 1, hash_tlsdesc, eq_tlsdesc); > if (! entry) > - { > - __rtld_lock_unlock_recursive (GL(dl_load_lock)); > - return 0; > - } > + return 0; > > if (*entry) > { > td = *entry; > - __rtld_lock_unlock_recursive (GL(dl_load_lock)); > return td; > } > Ok. > @@ -122,44 +116,9 @@ _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset) > thread. */ > td->gen_count = map_generation (map); > td->tlsinfo = test.tlsinfo; > - > - __rtld_lock_unlock_recursive (GL(dl_load_lock)); > return td; > } > > # endif /* SHARED */ > > -/* The idea of the following two functions is to stop multiple threads > - from attempting to resolve the same TLS descriptor without busy > - waiting. Ideally, we should be able to release the lock right > - after changing td->entry, and then using say a condition variable > - or a futex wake to wake up any waiting threads, but let's try to > - avoid introducing such dependencies. */ > - > -static int > -__attribute__ ((unused)) > -_dl_tlsdesc_resolve_early_return_p (struct tlsdesc volatile *td, void *caller) > -{ > - if (caller != atomic_load_relaxed (&td->entry)) > - return 1; > - > - __rtld_lock_lock_recursive (GL(dl_load_lock)); > - if (caller != atomic_load_relaxed (&td->entry)) > - { > - __rtld_lock_unlock_recursive (GL(dl_load_lock)); > - return 1; > - } > - > - atomic_store_relaxed (&td->entry, _dl_tlsdesc_resolve_hold); > - > - return 0; > -} > - > -static void > -__attribute__ ((unused)) > -_dl_tlsdesc_wake_up_held_fixups (void) > -{ > - __rtld_lock_unlock_recursive (GL(dl_load_lock)); > -} > - > #endif Ok. > diff --git a/sysdeps/aarch64/tlsdesc.c b/sysdeps/aarch64/tlsdesc.c > index 9b6a8b0ec4..3c1bcd8fe6 100644 > --- a/sysdeps/aarch64/tlsdesc.c > +++ b/sysdeps/aarch64/tlsdesc.c > @@ -22,7 +22,6 @@ > #include <tls.h> > #include <dl-tlsdesc.h> > #include <dl-unmap-segments.h> > -#define _dl_tlsdesc_resolve_hold 0 > #include <tlsdeschtab.h> > > /* Unmap the dynamic object, but also release its TLS descriptor table Ok. > diff --git a/sysdeps/arm/tlsdesc.c b/sysdeps/arm/tlsdesc.c > index 2f70adef5c..b3d1735af4 100644 > --- a/sysdeps/arm/tlsdesc.c > +++ b/sysdeps/arm/tlsdesc.c > @@ -20,7 +20,6 @@ > #include <tls.h> > #include <dl-tlsdesc.h> > #include <dl-unmap-segments.h> > -#define _dl_tlsdesc_resolve_hold 0 > #include <tlsdeschtab.h> > > /* Unmap the dynamic object, but also release its TLS descriptor table Ok. > diff --git a/sysdeps/i386/tlsdesc.c b/sysdeps/i386/tlsdesc.c > index 436a21f66b..364c7769ce 100644 > --- a/sysdeps/i386/tlsdesc.c > +++ b/sysdeps/i386/tlsdesc.c > @@ -20,7 +20,6 @@ > #include <tls.h> > #include <dl-tlsdesc.h> > #include <dl-unmap-segments.h> > -#define _dl_tlsdesc_resolve_hold 0 > #include <tlsdeschtab.h> > > /* Unmap the dynamic object, but also release its TLS descriptor table Ok. > diff --git a/sysdeps/x86_64/tlsdesc.c b/sysdeps/x86_64/tlsdesc.c > index ecf864d6ee..3bb80517a3 100644 > --- a/sysdeps/x86_64/tlsdesc.c > +++ b/sysdeps/x86_64/tlsdesc.c > @@ -20,7 +20,6 @@ > #include <tls.h> > #include <dl-tlsdesc.h> > #include <dl-unmap-segments.h> > -#define _dl_tlsdesc_resolve_hold 0 > #include <tlsdeschtab.h> > > /* Unmap the dynamic object, but also release its TLS descriptor table > Ok.
diff --git a/elf/tlsdeschtab.h b/elf/tlsdeschtab.h index 21695fd1e9..85bd0415e1 100644 --- a/elf/tlsdeschtab.h +++ b/elf/tlsdeschtab.h @@ -78,6 +78,10 @@ map_generation (struct link_map *map) return GL(dl_tls_generation) + 1; } +/* Returns the data pointer for a given map and tls offset that is used + to fill in one of the GOT entries referenced by a TLSDESC relocation + when using dynamic TLS. This requires allocation, returns NULL on + allocation failure. */ void * _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset) { @@ -85,18 +89,12 @@ _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset) void **entry; struct tlsdesc_dynamic_arg *td, test; - /* FIXME: We could use a per-map lock here, but is it worth it? */ - __rtld_lock_lock_recursive (GL(dl_load_lock)); - ht = map->l_mach.tlsdesc_table; if (! ht) { ht = htab_create (); if (! ht) - { - __rtld_lock_unlock_recursive (GL(dl_load_lock)); - return 0; - } + return 0; map->l_mach.tlsdesc_table = ht; } @@ -104,15 +102,11 @@ _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset) test.tlsinfo.ti_offset = ti_offset; entry = htab_find_slot (ht, &test, 1, hash_tlsdesc, eq_tlsdesc); if (! entry) - { - __rtld_lock_unlock_recursive (GL(dl_load_lock)); - return 0; - } + return 0; if (*entry) { td = *entry; - __rtld_lock_unlock_recursive (GL(dl_load_lock)); return td; } @@ -122,44 +116,9 @@ _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset) thread. */ td->gen_count = map_generation (map); td->tlsinfo = test.tlsinfo; - - __rtld_lock_unlock_recursive (GL(dl_load_lock)); return td; } # endif /* SHARED */ -/* The idea of the following two functions is to stop multiple threads - from attempting to resolve the same TLS descriptor without busy - waiting. Ideally, we should be able to release the lock right - after changing td->entry, and then using say a condition variable - or a futex wake to wake up any waiting threads, but let's try to - avoid introducing such dependencies. */ - -static int -__attribute__ ((unused)) -_dl_tlsdesc_resolve_early_return_p (struct tlsdesc volatile *td, void *caller) -{ - if (caller != atomic_load_relaxed (&td->entry)) - return 1; - - __rtld_lock_lock_recursive (GL(dl_load_lock)); - if (caller != atomic_load_relaxed (&td->entry)) - { - __rtld_lock_unlock_recursive (GL(dl_load_lock)); - return 1; - } - - atomic_store_relaxed (&td->entry, _dl_tlsdesc_resolve_hold); - - return 0; -} - -static void -__attribute__ ((unused)) -_dl_tlsdesc_wake_up_held_fixups (void) -{ - __rtld_lock_unlock_recursive (GL(dl_load_lock)); -} - #endif diff --git a/sysdeps/aarch64/tlsdesc.c b/sysdeps/aarch64/tlsdesc.c index 9b6a8b0ec4..3c1bcd8fe6 100644 --- a/sysdeps/aarch64/tlsdesc.c +++ b/sysdeps/aarch64/tlsdesc.c @@ -22,7 +22,6 @@ #include <tls.h> #include <dl-tlsdesc.h> #include <dl-unmap-segments.h> -#define _dl_tlsdesc_resolve_hold 0 #include <tlsdeschtab.h> /* Unmap the dynamic object, but also release its TLS descriptor table diff --git a/sysdeps/arm/tlsdesc.c b/sysdeps/arm/tlsdesc.c index 2f70adef5c..b3d1735af4 100644 --- a/sysdeps/arm/tlsdesc.c +++ b/sysdeps/arm/tlsdesc.c @@ -20,7 +20,6 @@ #include <tls.h> #include <dl-tlsdesc.h> #include <dl-unmap-segments.h> -#define _dl_tlsdesc_resolve_hold 0 #include <tlsdeschtab.h> /* Unmap the dynamic object, but also release its TLS descriptor table diff --git a/sysdeps/i386/tlsdesc.c b/sysdeps/i386/tlsdesc.c index 436a21f66b..364c7769ce 100644 --- a/sysdeps/i386/tlsdesc.c +++ b/sysdeps/i386/tlsdesc.c @@ -20,7 +20,6 @@ #include <tls.h> #include <dl-tlsdesc.h> #include <dl-unmap-segments.h> -#define _dl_tlsdesc_resolve_hold 0 #include <tlsdeschtab.h> /* Unmap the dynamic object, but also release its TLS descriptor table diff --git a/sysdeps/x86_64/tlsdesc.c b/sysdeps/x86_64/tlsdesc.c index ecf864d6ee..3bb80517a3 100644 --- a/sysdeps/x86_64/tlsdesc.c +++ b/sysdeps/x86_64/tlsdesc.c @@ -20,7 +20,6 @@ #include <tls.h> #include <dl-tlsdesc.h> #include <dl-unmap-segments.h> -#define _dl_tlsdesc_resolve_hold 0 #include <tlsdeschtab.h> /* Unmap the dynamic object, but also release its TLS descriptor table