ceph: Fix race between hole punch and page fault

Ceph has a following race between hole punching and page fault:

CPU1                                  CPU2
ceph_fallocate()
  ...
  ceph_zero_pagecache_range()
                                      ceph_filemap_fault()
                                        faults in page in the range being
                                        punched
  ceph_zero_objects()

And now we have a page in punched range with invalid data. Fix the
problem by using mapping->invalidate_lock similarly to other
filesystems. Note that using invalidate_lock also fixes a similar race
wrt ->readpage().

CC: Jeff Layton <jlayton@kernel.org>
CC: ceph-devel@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index a1e2813731d1..7e7a897ae0d3 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -1395,9 +1395,11 @@ static vm_fault_t ceph_filemap_fault(struct vm_fault *vmf)
 		ret = VM_FAULT_SIGBUS;
 	} else {
 		struct address_space *mapping = inode->i_mapping;
-		struct page *page = find_or_create_page(mapping, 0,
-						mapping_gfp_constraint(mapping,
-						~__GFP_FS));
+		struct page *page;
+
+		filemap_invalidate_lock_shared(mapping);
+		page = find_or_create_page(mapping, 0,
+				mapping_gfp_constraint(mapping, ~__GFP_FS));
 		if (!page) {
 			ret = VM_FAULT_OOM;
 			goto out_inline;
@@ -1418,6 +1420,7 @@ static vm_fault_t ceph_filemap_fault(struct vm_fault *vmf)
 		vmf->page = page;
 		ret = VM_FAULT_MAJOR | VM_FAULT_LOCKED;
 out_inline:
+		filemap_invalidate_unlock_shared(mapping);
 		dout("filemap_fault %p %llu read inline data ret %x\n",
 		     inode, off, ret);
 	}