[PATCH] SUNRPC/cache: don't allow invalid entries to be flushed

["J. Bruce Fields" <bfields@redhat.com>]

From: "J. Bruce Fields" <bfields@redhat.com>

Trond points out in 277f27e2f277 that we allow invalid cache entries to
persist indefinitely.  That fix, however, reintroduces the problem fixed
by Kinglong Mee's d6fc8821c2d2 "SUNRPC/Cache: Always treat the invalid
cache as unexpired", where an invalid cache entry is immediately removed
by a flush before mountd responds to it.  The result is that the server
thread that should be waiting for mountd to fill in that entry instead
gets an -ETIMEDOUT return from cache_check().  Symptoms are the server
becoming unresponsive after a restart, reproduceable by running pynfs
4.1 test REBT5.

Instead, take a compromise approach: allow invalid cache entries to be
removed after they expire, but not to be removed by a cache flush.

Fixes: 277f27e2f277 "SUNRPC/cache: Allow garbage collection..."
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---
 include/linux/sunrpc/cache.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
index 532cdbda43da..10891b70fc7b 100644
--- a/include/linux/sunrpc/cache.h
+++ b/include/linux/sunrpc/cache.h
@@ -209,8 +209,11 @@ static inline void cache_put(struct cache_head *h, struct cache_detail *cd)
 
 static inline bool cache_is_expired(struct cache_detail *detail, struct cache_head *h)
 {
-	return  (h->expiry_time < seconds_since_boot()) ||
-		(detail->flush_time >= h->last_refresh);
+	if (h->expiry_time < seconds_since_boot())
+		return true;
+	if (!test_bit(CACHE_VALID, &h->flags))
+		return false;
+	return detail->flush_time >= h->last_refresh;
 }
 
 extern int cache_check(struct cache_detail *detail,
-- 
2.25.1