Received-SPF: pass (google.com: best guess record for domain of linux-nfs-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 27 Mar 2020 11:53:09 -0400
From:   "J. Bruce Fields" <bfields@redhat.com>
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Trond Myklebust <trondmy@hammerspace.com>,
        "bfields@fieldses.org" <bfields@fieldses.org>,
        "kinglongmee@gmail.com" <kinglongmee@gmail.com>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: [PATCH] SUNRPC/cache: don't allow invalid entries to be flushed
Message-ID: <20200327155309.GA135601@pick.fieldses.org>
References: <20200114165738.922961-1-trond.myklebust@hammerspace.com>
 <20200206163322.GB2244@fieldses.org>
 <8dc1ed17de98e4b59fb9e408692c152456863a20.camel@hammerspace.com>
 <20200207181817.GC17036@fieldses.org>
 <20200326204001.GA25053@fieldses.org>
 <1a0ce8bb1150835f7a25126df2524e8a8fb0e112.camel@hammerspace.com>
 <20200327015012.GA107036@pick.fieldses.org>
 <80c83f5543d7d758a165be167d3bf0b2175e57f8.camel@hammerspace.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <80c83f5543d7d758a165be167d3bf0b2175e57f8.camel@hammerspace.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

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