linux-ext4 - [PATCH 13/14] ceph: Fix race between hole punch and page fault

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Message-Id: <20210712165609.13215-13-jack@suse.cz>
Date:   Mon, 12 Jul 2021 18:56:04 +0200
From:   Jan Kara <jack@...e.cz>
To:     <linux-fsdevel@...r.kernel.org>
Cc:     <linux-ext4@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J. Wong" <djwong@...nel.org>, Ted Tso <tytso@....edu>,
        Dave Chinner <david@...morbit.com>,
        Matthew Wilcox <willy@...radead.org>, <linux-mm@...ck.org>,
        <linux-xfs@...r.kernel.org>,
        linux-f2fs-devel@...ts.sourceforge.net, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>
Subject: [PATCH 13/14] 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@...nel.org>
CC: ceph-devel@...r.kernel.org
Reviewed-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ceph/addr.c | 9 ++++++---
 fs/ceph/file.c | 2 ++
 2 files changed, 8 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);
 	}
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index d1755ac1d964..e1d605a02d4a 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -2088,6 +2088,7 @@ static long ceph_fallocate(struct file *file, int mode,
 	if (ret < 0)
 		goto unlock;
 
+	filemap_invalidate_lock(inode->i_mapping);
 	ceph_zero_pagecache_range(inode, offset, length);
 	ret = ceph_zero_objects(inode, offset, length);
 
@@ -2100,6 +2101,7 @@ static long ceph_fallocate(struct file *file, int mode,
 		if (dirty)
 			__mark_inode_dirty(inode, dirty);
 	}
+	filemap_invalidate_unlock(inode->i_mapping);
 
 	ceph_put_cap_refs(ci, got);
 unlock:
-- 
2.26.2