diff options
| -rw-r--r-- | elf/dl-load.c | 18 | ||||
| -rw-r--r-- | elf/dl-misc.c | 4 |
2 files changed, 20 insertions, 2 deletions
diff --git a/elf/dl-load.c b/elf/dl-load.c index 9e2089c..be54baf 100644 --- a/elf/dl-load.c +++ b/elf/dl-load.c @@ -438,7 +438,23 @@ add_name_to_object (struct link_map *l, const char *name) newname->name = memcpy (newname + 1, name, name_len); newname->next = NULL; newname->dont_free = 0; - lastp->next = newname; + /* CONCURRENCY NOTES: + + Make sure the initialization of newname happens before its address is + read from the lastp->next store below. + + GL(dl_load_lock) is held here (and by other writers, e.g. dlclose), so + readers of libname_list->next (e.g. _dl_check_caller or the reads above) + can use that for synchronization, however the read in _dl_name_match_p + may be executed without holding the lock during _dl_runtime_resolve + (i.e. lazy symbol resolution when a function of library l is called). + + The release MO store below synchronizes with the acquire MO load in + _dl_name_match_p. Other writes need to synchronize with that load too, + however those happen either early when the process is single threaded + (dl_main) or when the library is unloaded (dlclose) and the user has to + synchronize library calls with unloading. */ + atomic_store_release (&lastp->next, newname); } /* Standard search directories. */ diff --git a/elf/dl-misc.c b/elf/dl-misc.c index 082f75f..d4803bb 100644 --- a/elf/dl-misc.c +++ b/elf/dl-misc.c @@ -347,7 +347,9 @@ _dl_name_match_p (const char *name, const struct link_map *map) if (strcmp (name, runp->name) == 0) return 1; else - runp = runp->next; + /* Synchronize with the release MO store in add_name_to_object. + See CONCURRENCY NOTES in add_name_to_object in dl-load.c. */ + runp = atomic_load_acquire (&runp->next); return 0; } |