ceph: supply snapshot context in ceph_zero_partial_object()

The ceph_zero_partial_object function was missing proper snapshot
context for its OSD write operations, which could lead to data
inconsistencies in snapshots.

Reproducer:
../src/vstart.sh --new -x --localhost --bluestore
./bin/ceph auth caps client.fs_a mds 'allow rwps fsname=a' mon 'allow r fsname=a' osd 'allow rw tag cephfs data=a'
mount -t ceph fs_a@.a=/ /mnt/mycephfs/ -o conf=./ceph.conf
dd if=/dev/urandom of=/mnt/mycephfs/foo bs=64K count=1
mkdir /mnt/mycephfs/.snap/snap1
md5sum /mnt/mycephfs/.snap/snap1/foo
fallocate -p -o 0 -l 4096 /mnt/mycephfs/foo
echo 3 > /proc/sys/vm/drop/caches
md5sum /mnt/mycephfs/.snap/snap1/foo # get different md5sum!!

Cc: stable@vger.kernel.org
Fixes: ad7a60d ("ceph: punch hole support")
Signed-off-by: ethanwu <ethanwu@synology.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Tested-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: ethanwu-syno

fs/ceph/file.c

@@ -2568,6 +2568,7 @@ static int ceph_zero_partial_object(struct inode *inode,
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	struct ceph_fs_client *fsc = ceph_inode_to_fs_client(inode);
 	struct ceph_osd_request *req;
+	struct ceph_snap_context *snapc;
 	int ret = 0;
 	loff_t zero = 0;
 	int op;
@@ -2582,12 +2583,25 @@ static int ceph_zero_partial_object(struct inode *inode,
 		op = CEPH_OSD_OP_ZERO;
 	}
 
+	spin_lock(&ci->i_ceph_lock);
+	if (__ceph_have_pending_cap_snap(ci)) {
+		struct ceph_cap_snap *capsnap =
+				list_last_entry(&ci->i_cap_snaps,
+						struct ceph_cap_snap,
+						ci_item);
+		snapc = ceph_get_snap_context(capsnap->context);
+	} else {
+		BUG_ON(!ci->i_head_snapc);
+		snapc = ceph_get_snap_context(ci->i_head_snapc);
+	}
+	spin_unlock(&ci->i_ceph_lock);
+
 	req = ceph_osdc_new_request(&fsc->client->osdc, &ci->i_layout,
 					ceph_vino(inode),
 					offset, length,
 					0, 1, op,
 					CEPH_OSD_FLAG_WRITE,
-					NULL, 0, 0, false);
+					snapc, 0, 0, false);
 	if (IS_ERR(req)) {
 		ret = PTR_ERR(req);
 		goto out;
@@ -2601,6 +2615,7 @@ static int ceph_zero_partial_object(struct inode *inode,
 	ceph_osdc_put_request(req);
 
 out:
+	ceph_put_snap_context(snapc);
 	return ret;
 }