linux-kernel - [PATCH v4 03/10] cachefiles: Always indicate we should fill a post-EOF page with zeros

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Message-ID: <163551659286.1877519.2951437510049163050.stgit@warthog.procyon.org.uk>
Date:   Fri, 29 Oct 2021 15:09:52 +0100
From:   David Howells <dhowells@...hat.com>
To:     Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>
Cc:     dhowells@...hat.com, Jeff Layton <jlayton@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 03/10] cachefiles: Always indicate we should fill a
 post-EOF page with zeros

In cachefiles_prepare_read(), always indicate to the netfs lib that a page
beyond the EOF should be filled with zeros, even if we don't have a cache
file attached because it's still being created.

This avoids confusion in netfs_rreq_prepare_read() where it sees source ==
NETFS_DOWNLOAD_FROM_SERVER, where it consequently sees the read after the
EOF getting reduced to 0 size and thus triggers the WARN_ON and marking the
read invalid.

Also don't try to check for data if there's a flag set indicating we don't
yet have anything stored in the cache.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/cachefiles/io.c |   29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index 08b3183e0dce..dbc1c4421116 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -273,6 +273,7 @@ static enum netfs_read_source cachefiles_prepare_read(struct netfs_read_subreque
 	struct cachefiles_cache *cache;
 	const struct cred *saved_cred;
 	struct file *file = subreq->rreq->cache_resources.cache_priv2;
+	enum netfs_read_source ret = NETFS_DOWNLOAD_FROM_SERVER;
 	loff_t off, to;
 
 	_enter("%zx @%llx/%llx", subreq->len, subreq->start, i_size);
@@ -281,19 +282,24 @@ static enum netfs_read_source cachefiles_prepare_read(struct netfs_read_subreque
 	cache = container_of(object->fscache.cache,
 			     struct cachefiles_cache, cache);
 
-	if (!file)
-		goto cache_fail_nosec;
+	cachefiles_begin_secure(cache, &saved_cred);
 
-	if (subreq->start >= i_size)
-		return NETFS_FILL_WITH_ZEROES;
+	if (subreq->start >= i_size) {
+		ret = NETFS_FILL_WITH_ZEROES;
+		goto out;
+	}
 
-	cachefiles_begin_secure(cache, &saved_cred);
+	if (!file)
+		goto out;
+
+	if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->fscache.cookie->flags))
+		goto download_and_store;
 
 	off = vfs_llseek(file, subreq->start, SEEK_DATA);
 	if (off < 0 && off >= (loff_t)-MAX_ERRNO) {
 		if (off == (loff_t)-ENXIO)
 			goto download_and_store;
-		goto cache_fail;
+		goto out;
 	}
 
 	if (off >= subreq->start + subreq->len)
@@ -307,7 +313,7 @@ static enum netfs_read_source cachefiles_prepare_read(struct netfs_read_subreque
 
 	to = vfs_llseek(file, subreq->start, SEEK_HOLE);
 	if (to < 0 && to >= (loff_t)-MAX_ERRNO)
-		goto cache_fail;
+		goto out;
 
 	if (to < subreq->start + subreq->len) {
 		if (subreq->start + subreq->len >= i_size)
@@ -317,16 +323,15 @@ static enum netfs_read_source cachefiles_prepare_read(struct netfs_read_subreque
 		subreq->len = to - subreq->start;
 	}
 
-	cachefiles_end_secure(cache, saved_cred);
-	return NETFS_READ_FROM_CACHE;
+	ret = NETFS_READ_FROM_CACHE;
+	goto out;
 
 download_and_store:
 	if (cachefiles_has_space(cache, 0, (subreq->len + PAGE_SIZE - 1) / PAGE_SIZE) == 0)
 		__set_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags);
-cache_fail:
+out:
 	cachefiles_end_secure(cache, saved_cred);
-cache_fail_nosec:
-	return NETFS_DOWNLOAD_FROM_SERVER;
+	return ret;
 }
 
 /*