diff options
| -rw-r--r-- | elf/dl-tls.c | 63 |
1 files changed, 47 insertions, 16 deletions
diff --git a/elf/dl-tls.c b/elf/dl-tls.c index f8b32b3ecb..33c06782b1 100644 --- a/elf/dl-tls.c +++ b/elf/dl-tls.c @@ -471,14 +471,11 @@ extern dtv_t _dl_static_dtv[]; #endif static dtv_t * -_dl_resize_dtv (dtv_t *dtv) +_dl_resize_dtv (dtv_t *dtv, size_t max_modid) { /* Resize the dtv. */ dtv_t *newp; - /* Load GL(dl_tls_max_dtv_idx) atomically since it may be written to by - other threads concurrently. */ - size_t newsize - = atomic_load_acquire (&GL(dl_tls_max_dtv_idx)) + DTV_SURPLUS; + size_t newsize = max_modid + DTV_SURPLUS; size_t oldsize = dtv[-1].counter; if (dtv == GL(dl_initial_dtv)) @@ -524,11 +521,14 @@ _dl_allocate_tls_init (void *result) size_t total = 0; size_t maxgen = 0; + /* Protects global dynamic TLS related state. */ + __rtld_lock_lock_recursive (GL(dl_load_lock)); + /* Check if the current dtv is big enough. */ if (dtv[-1].counter < GL(dl_tls_max_dtv_idx)) { /* Resize the dtv. */ - dtv = _dl_resize_dtv (dtv); + dtv = _dl_resize_dtv (dtv, GL(dl_tls_max_dtv_idx)); /* Install this new dtv in the thread data structures. */ INSTALL_DTV (result, &dtv[-1]); @@ -596,6 +596,7 @@ _dl_allocate_tls_init (void *result) listp = listp->next; assert (listp != NULL); } + __rtld_lock_unlock_recursive (GL(dl_load_lock)); /* The DTV version is up-to-date now. */ dtv[0].counter = maxgen; @@ -730,12 +731,29 @@ _dl_update_slotinfo (unsigned long int req_modid) if (dtv[0].counter < listp->slotinfo[idx].gen) { - /* The generation counter for the slot is higher than what the - current dtv implements. We have to update the whole dtv but - only those entries with a generation counter <= the one for - the entry we need. */ + /* CONCURRENCY NOTES: + + Here the dtv needs to be updated to new_gen generation count. + + This code may be called during TLS access when GL(dl_load_lock) + is not held. In that case the user code has to synchrnize with + dlopen and dlclose calls of relevant modules. A module m is + relevant if the generation of m <= new_gen and dlclose of m is + synchronized: a memory access here happens after the dlopen and + before the dlclose of relevant modules. The dtv entries for + relevant modules need to be updated, other entries can be + arbitrary. + + This e.g. means that the first part of the slotinfo list can be + accessed race free, but the tail may be concurrently extended. + Similarly relevant slotinfo entries can be read race free, but + other entries are racy. However updating a non-relevant dtv + entry does not affect correctness. For a relevant module m, + max_modid >= modid of m. */ size_t new_gen = listp->slotinfo[idx].gen; size_t total = 0; + size_t max_modid = atomic_load_relaxed (&GL(dl_tls_max_dtv_idx)); + assert (max_modid >= req_modid); /* We have to look through the entire dtv slotinfo list. */ listp = GL(dl_tls_dtv_slotinfo_list); @@ -745,12 +763,14 @@ _dl_update_slotinfo (unsigned long int req_modid) { size_t modid = total + cnt; + /* Later entries are not relevant. */ + if (modid > max_modid) + break; + size_t gen = listp->slotinfo[cnt].gen; if (gen > new_gen) - /* This is a slot for a generation younger than the - one we are handling now. It might be incompletely - set up so ignore it. */ + /* Not relevant. */ continue; /* If the entry is older than the current dtv layout we @@ -767,7 +787,7 @@ _dl_update_slotinfo (unsigned long int req_modid) continue; /* Resize the dtv. */ - dtv = _dl_resize_dtv (dtv); + dtv = _dl_resize_dtv (dtv, max_modid); assert (modid <= dtv[-1].counter); @@ -789,8 +809,17 @@ _dl_update_slotinfo (unsigned long int req_modid) } total += listp->len; + if (total > max_modid) + break; + + /* Synchronize with _dl_add_to_slotinfo. Ideally this would + be consume MO since we only need to order the accesses to + the next node after the read of the address and on most + hardware (other than alpha) a normal load would do that + because of the address dependency. */ + listp = atomic_load_acquire (&listp->next); } - while ((listp = listp->next) != NULL); + while (listp != NULL); /* This will be the new maximum generation counter. */ dtv[0].counter = new_gen; @@ -982,7 +1011,7 @@ _dl_add_to_slotinfo (struct link_map *l, bool do_add) the first slot. */ assert (idx == 0); - listp = prevp->next = (struct dtv_slotinfo_list *) + listp = (struct dtv_slotinfo_list *) malloc (sizeof (struct dtv_slotinfo_list) + TLS_SLOTINFO_SURPLUS * sizeof (struct dtv_slotinfo)); if (listp == NULL) @@ -996,6 +1025,8 @@ cannot create TLS data structures")); listp->next = NULL; memset (listp->slotinfo, '\0', TLS_SLOTINFO_SURPLUS * sizeof (struct dtv_slotinfo)); + /* Synchronize with _dl_update_slotinfo. */ + atomic_store_release (&prevp->next, listp); } /* Add the information into the slotinfo data structure. */ |