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sunrpc: fix race in cache cleanup causing stale nextcheck time

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When cache cleanup runs concurrently with cache entry removal, a race
condition can occur that leads to incorrect nextcheck times. This can
delay cache cleanup for the cache_detail by up to 1800 seconds:

1. cache_clean() sets nextcheck to current time plus 1800 seconds
2. While scanning a non-empty bucket, concurrent cache entry removal can
   empty that bucket
3. cache_clean() finds no cache entries in the now-empty bucket to update
   the nextcheck time
4. This maybe delays the next scan of the cache_detail by up to 1800
   seconds even when it should be scanned earlier based on remaining
   entries

Fix this by moving the hash_lock acquisition earlier in cache_clean().
This ensures bucket emptiness checks and nextcheck updates happen
atomically, preventing the race between cleanup and entry removal.

Signed-off-by: Long Li <leo.lilong@huawei.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Long Li
2025-03-01 14:48:36 +08:00
committed by Chuck Lever
parent 5ca00634c8
commit 2298abcbe1
1 changed files with 7 additions and 8 deletions
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15
net/sunrpc/cache.c
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@@ -464,24 +464,21 @@ static int cache_clean(void)
}
}
spin_lock(&current_detail->hash_lock);
/* find a non-empty bucket in the table */
while (current_detail &&
current_index < current_detail->hash_size &&
while (current_index < current_detail->hash_size &&
hlist_empty(&current_detail->hash_table[current_index]))
current_index++;
/* find a cleanable entry in the bucket and clean it, or set to next bucket */
if (current_detail && current_index < current_detail->hash_size) {
if (current_index < current_detail->hash_size) {
struct cache_head *ch = NULL;
struct cache_detail *d;
struct hlist_head *head;
struct hlist_node *tmp;
spin_lock(&current_detail->hash_lock);
/* Ok, now to clean this strand */
head = &current_detail->hash_table[current_index];
hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
if (current_detail->nextcheck > ch->expiry_time)
@@ -502,8 +499,10 @@ static int cache_clean(void)
spin_unlock(&cache_list_lock);
if (ch)
sunrpc_end_cache_remove_entry(ch, d);
} else
} else {
spin_unlock(&current_detail->hash_lock);
spin_unlock(&cache_list_lock);
}
return rv;
}