sunrpc: clean cache_detail immediately when flush is written frequently

We will write /proc/net/rpc/xxx/flush if we want to clean cache_detail.
This updates nextcheck to the current time and calls cache_flush -->
cache_clean to clean cache_detail.
If we write this interface again within one second, it will only increase
flush_time and nextcheck without actually cleaning cache_detail.
Therefore, if we keep writing this interface repeatedly within one second,
flush_time and nextcheck will keep increasing, even far exceeding the
current time, making it impossible to clear cache_detail through the flush
interface or cache_cleaner.
If someone frequently calls the flush interface, we should immediately
clean the corresponding cache_detail instead of continuously accumulating
nextcheck.

Signed-off-by: Li Lingfeng <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>

Author: Li Lingfeng

net/sunrpc/cache.c

@@ -1536,9 +1536,13 @@ static ssize_t write_flush(struct file *file, const char __user *buf,
 	 * or by one second if it has already reached the current time.
 	 * Newly added cache entries will always have ->last_refresh greater
 	 * that ->flush_time, so they don't get flushed prematurely.
+	 *
+	 * If someone frequently calls the flush interface, we should
+	 * immediately clean the corresponding cache_detail instead of
+	 * continuously accumulating nextcheck.
 	 */
 
-	if (cd->flush_time >= now)
+	if (cd->flush_time >= now && cd->flush_time < (now + 5))
 		now = cd->flush_time + 1;
 
 	cd->flush_time = now;