Status: New
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 371 by [email protected]: slab re-balance is not thread-safty
in function do_item_get
http://code.google.com/p/memcached/issues/detail?id=371
It is not thread-safety to use do_item_unlink_nolock to delete the item
from LRU list in function do_item_get, without holding the cache_lock.
Please read the below link for more info:
https://groups.google.com/forum/#!topic/memcached/9RYy3B5SuPs
----------------------------
item *do_item_get(const char *key, const size_t nkey, const uint32_t hv) {
//mutex_lock(&cache_lock);
item *it = assoc_find(key, nkey, hv);
if (it != NULL) {
refcount_incr(&it->refcount);
/* Optimization for slab reassignment. prevents popular items from
* jamming in busy wait. Can only do this here to satisfy lock order
* of item_lock, cache_lock, slabs_lock. */
if (slab_rebalance_signal &&
((void *)it >= slab_rebal.slab_start && (void *)it <
slab_rebal.slab_end)) {
do_item_unlink_nolock(it, hv);
do_item_remove(it);
it = NULL;
}
}
//mutex_unlock(&cache_lock);
int was_found = 0;
if (settings.verbose > 2) {
int ii;
if (it == NULL) {
fprintf(stderr, "> NOT FOUND ");
} else {
fprintf(stderr, "> FOUND KEY ");
was_found++;
}
for (ii = 0; ii < nkey; ++ii) {
fprintf(stderr, "%c", key[ii]);
}
}
if (it != NULL) {
if (settings.oldest_live != 0 && settings.oldest_live <=
current_time &&
it->time <= settings.oldest_live) {
do_item_unlink(it, hv);
do_item_remove(it);
it = NULL;
if (was_found) {
fprintf(stderr, " -nuked by flush");
}
} else if (it->exptime != 0 && it->exptime <= current_time) {
do_item_unlink(it, hv);
do_item_remove(it);
it = NULL;
if (was_found) {
fprintf(stderr, " -nuked by expire");
}
} else {
it->it_flags |= ITEM_FETCHED;
DEBUG_REFCNT(it, '+');
}
}
if (settings.verbose > 2)
fprintf(stderr, "\n");
return it;
}
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