[PATCH 5.15 291/411] sunrpc: fix race in cache cleanup causing stale nextcheck time

5.15-stable review patch. If anyone has any objections, please let me know.

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From: Long Li leo.lilong@huawei.com

[ Upstream commit 2298abcbe11e9b553d03c0f1d084da786f7eff88 ]

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 Signed-off-by: Sasha Levin sashal@kernel.org --- net/sunrpc/cache.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c index e8448e9e03d59..715f7d080f7a2 100644 --- a/net/sunrpc/cache.c +++ b/net/sunrpc/cache.c @@ -451,24 +451,21 @@ 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) @@ -489,8 +486,10 @@ 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; }