[PATCH 5.13 264/351] NFS: Fix fscache read from NFS after cache error

Greg Kroah-Hartman
2021-07-19T17:51:08Z

From: Dave Wysochanski <dwysocha@redhat.com>

[ Upstream commit ba512c1bc3232124567a59a3995c773dc79716e8 ]

Earlier commits refactored some NFS read code and removed
nfs_readpage_async(), but neglected to properly fixup
nfs_readpage_from_fscache_complete(). The code path is
only hit when something unusual occurs with the cachefiles
backing filesystem, such as an IO error or while a cookie
is being invalidated.

Mark page with PG_checked if fscache IO completes in error,
unlock the page, and let the VM decide to re-issue based on
PG_uptodate. When the VM reissues the readpage, PG_checked
allows us to skip over fscache and read from the server.

Link: https://marc.info/?l=linux-nfs&m=162498209518739
Fixes: 1e83b173b266 ("NFS: Add nfs_pageio_complete_read() and remove nfs_readpage_async()")
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfs/fscache.c | 18 +++++++++++++-----
fs/nfs/read.c | 5 +++--
2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/fs/nfs/fscache.c b/fs/nfs/fscache.c
index c4c021c6ebbd..d743629e05e1 100644
--- a/fs/nfs/fscache.c
+++ b/fs/nfs/fscache.c
@@ -385,12 +385,15 @@ static void nfs_readpage_from_fscache_complete(struct page *page,
"NFS: readpage_from_fscache_complete (0x%p/0x%p/%d)\n",
page, context, error);

- /* if the read completes with an error, we just unlock the page and let
- * the VM reissue the readpage */
- if (!error) {
+ /*
+ * If the read completes with an error, mark the page with PG_checked,
+ * unlock the page, and let the VM reissue the readpage.
+ */
+ if (!error)
SetPageUptodate(page);
- unlock_page(page);
- }
+ else
+ SetPageChecked(page);
+ unlock_page(page);
}

/*
@@ -405,6 +408,11 @@ int __nfs_readpage_from_fscache(struct nfs_open_context *ctx,
"NFS: readpage_from_fscache(fsc:%p/p:%p(i:%lx f:%lx)/0x%p)\n",
nfs_i_fscache(inode), page, page->index, page->flags, inode);

+ if (PageChecked(page)) {
+ ClearPageChecked(page);
+ return 1;
+ }
+
ret = fscache_read_or_alloc_page(nfs_i_fscache(inode),
page,
nfs_readpage_from_fscache_complete,
diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index d2b6dce1f99f..4ca50b70a7b0 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -363,13 +363,13 @@ int nfs_readpage(struct file *file, struct page *page)
} else
desc.ctx = get_nfs_open_context(nfs_file_open_context(file));

+ xchg(&desc.ctx->error, 0);
if (!IS_SYNC(inode)) {
ret = nfs_readpage_from_fscache(desc.ctx, inode, page);
if (ret == 0)
- goto out;
+ goto out_wait;
}

- xchg(&desc.ctx->error, 0);
nfs_pageio_init_read(&desc.pgio, inode, false,
&nfs_async_read_completion_ops);

@@ -379,6 +379,7 @@ int nfs_readpage(struct file *file, struct page *page)
nfs_pageio_complete_read(&desc.pgio, inode);

ret = desc.pgio.pg_error < 0 ? desc.pgio.pg_error : 0;
+out_wait:
if (!ret) {
ret = wait_on_page_locked_killable(page);
if (!PageUptodate(page) && !ret)
--
2.30.2