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--- c/nscd/nscd_gethst_r.c 2012-01-01 05:16:32.000000000 -0700
+++ c/nscd/nscd_gethst_r.c 2012-03-28 10:45:51.546600822 -0600
@@ -101,9 +101,27 @@ libc_freeres_fn (hst_map_free)
uint32_t
__nscd_get_nl_timestamp (void)
{
+ uint32_t retval;
if (__nss_not_use_nscd_hosts != 0)
return 0;
+ int cnt = 0;
+ /* __nscd_get_mapping can change hst_map_handle.mapped to NO_MAPPING.
+ However, __nscd_get_mapping assumes the prior value was not NO_MAPPING.
+ Thus we have to acquire the lock to prevent this thread from changing
+ hst_map_handle.mapped to NO_MAPPING while another thread is inside
+ __nscd_get_mapping. */
+ while (__builtin_expect
+ (atomic_compare_and_exchange_val_acq (&__hst_map_handle.lock,
+ 1, 0) != 0, 0))
+ {
+ // XXX Best number of rounds?
+ if (__builtin_expect (++cnt > 5, 0))
+ return 0;
+
+ atomic_delay ();
+ }
+
struct mapped_database *map = __hst_map_handle.mapped;
if (map == NULL
@@ -113,9 +131,14 @@ __nscd_get_nl_timestamp (void)
map = __nscd_get_mapping (GETFDHST, "hosts", &__hst_map_handle.mapped);
if (map == NO_MAPPING)
- return 0;
+ retval = 0;
+ else
+ retval = map->head->extra_data[NSCD_HST_IDX_CONF_TIMESTAMP];
+
+ /* Release the lock. */
+ __hst_map_handle.lock = 0;
- return map->head->extra_data[NSCD_HST_IDX_CONF_TIMESTAMP];
+ return retval;
}
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