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authorDavid Howells <dhowells@redhat.com>2023-07-27 19:21:17 +0300
committerChuck Lever <chuck.lever@oracle.com>2023-07-31 01:07:12 +0300
commit101df45e7ec36f470559c8fdab8e272cb991ef42 (patch)
tree83e561a118544d07ec8a90c0d46a3092a072b78f /fs/nfsd
parentf75546f58a70da5cfdcec5a45ffc377885ccbee8 (diff)
downloadlinux-101df45e7ec36f470559c8fdab8e272cb991ef42.tar.xz
nfsd: Fix reading via splice
nfsd_splice_actor() has a clause in its loop that chops up a compound page into individual pages such that if the same page is seen twice in a row, it is discarded the second time. This is a problem with the advent of shmem_splice_read() as that inserts zero_pages into the pipe in lieu of pages that aren't present in the pagecache. Fix this by assuming that the last page is being extended only if the currently stored length + starting offset is not currently on a page boundary. This can be tested by NFS-exporting a tmpfs filesystem on the test machine and truncating it to more than a page in size (eg. truncate -s 8192) and then reading it by NFS. The first page will be all zeros, but thereafter garbage will be read. Note: I wonder if we can ever get a situation now where we get a splice that gives us contiguous parts of a page in separate actor calls. As NFSD can only be splicing from a file (I think), there are only three sources of the page: copy_splice_read(), shmem_splice_read() and file_splice_read(). The first allocates pages for the data it reads, so the problem cannot occur; the second should never see a partial page; and the third waits for each page to become available before we're allowed to read from it. Fixes: bd194b187115 ("shmem: Implement splice-read") Reported-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Reviewed-by: NeilBrown <neilb@suse.de> cc: Hugh Dickins <hughd@google.com> cc: Jens Axboe <axboe@kernel.dk> cc: Matthew Wilcox <willy@infradead.org> cc: linux-nfs@vger.kernel.org cc: linux-fsdevel@vger.kernel.org cc: linux-mm@kvack.org Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Diffstat (limited to 'fs/nfsd')
-rw-r--r--fs/nfsd/vfs.c9
1 files changed, 6 insertions, 3 deletions
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 59b7d60ae33e..ee3bbaa79478 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -956,10 +956,13 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
last_page = page + (offset + sd->len - 1) / PAGE_SIZE;
for (page += offset / PAGE_SIZE; page <= last_page; page++) {
/*
- * Skip page replacement when extending the contents
- * of the current page.
+ * Skip page replacement when extending the contents of the
+ * current page. But note that we may get two zero_pages in a
+ * row from shmem.
*/
- if (page == *(rqstp->rq_next_page - 1))
+ if (page == *(rqstp->rq_next_page - 1) &&
+ offset_in_page(rqstp->rq_res.page_base +
+ rqstp->rq_res.page_len))
continue;
if (unlikely(!svc_rqst_replace_page(rqstp, page)))
return -EIO;