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[PATCH 4.9 04/41] ceph: choose readdir frag based on previous readdir reply

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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yan, Zheng <zyan@redhat.com>

commit b50c2de51e611da90cf3cf04c058f7e9bbe79e93 upstream.

The dirfragtree is lazily updated, it's not always accurate. Infinite
loops happens in following circumstance.

- client send request to read frag A
- frag A has been fragmented into frag B and C. So mds fills the reply
  with contents of frag B
- client wants to read next frag C. ceph_choose_frag(frag value of C)
  return frag A.

The fix is using previous readdir reply to calculate next readdir frag
when possible.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/ceph/dir.c |   19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -315,7 +315,7 @@ static int ceph_readdir(struct file *fil
 	struct ceph_mds_client *mdsc = fsc->mdsc;
 	int i;
 	int err;
-	u32 ftype;
+	unsigned frag = -1;
 	struct ceph_mds_reply_info_parsed *rinfo;
 
 	dout("readdir %p file %p pos %llx\n", inode, file, ctx->pos);
@@ -362,7 +362,6 @@ more:
 	/* do we have the correct frag content buffered? */
 	if (need_send_readdir(fi, ctx->pos)) {
 		struct ceph_mds_request *req;
-		unsigned frag;
 		int op = ceph_snap(inode) == CEPH_SNAPDIR ?
 			CEPH_MDS_OP_LSSNAP : CEPH_MDS_OP_READDIR;
 
@@ -373,8 +372,11 @@ more:
 		}
 
 		if (is_hash_order(ctx->pos)) {
-			frag = ceph_choose_frag(ci, fpos_hash(ctx->pos),
-						NULL, NULL);
+			/* fragtree isn't always accurate. choose frag
+			 * based on previous reply when possible. */
+			if (frag == (unsigned)-1)
+				frag = ceph_choose_frag(ci, fpos_hash(ctx->pos),
+							NULL, NULL);
 		} else {
 			frag = fpos_frag(ctx->pos);
 		}
@@ -497,6 +499,7 @@ more:
 		struct ceph_mds_reply_dir_entry *rde = rinfo->dir_entries + i;
 		struct ceph_vino vino;
 		ino_t ino;
+		u32 ftype;
 
 		BUG_ON(rde->offset < ctx->pos);
 
@@ -519,15 +522,17 @@ more:
 		ctx->pos++;
 	}
 
+	ceph_mdsc_put_request(fi->last_readdir);
+	fi->last_readdir = NULL;
+
 	if (fi->next_offset > 2) {
-		ceph_mdsc_put_request(fi->last_readdir);
-		fi->last_readdir = NULL;
+		frag = fi->frag;
 		goto more;
 	}
 
 	/* more frags? */
 	if (!ceph_frag_is_rightmost(fi->frag)) {
-		unsigned frag = ceph_frag_next(fi->frag);
+		frag = ceph_frag_next(fi->frag);
 		if (is_hash_order(ctx->pos)) {
 			loff_t new_pos = ceph_make_fpos(ceph_frag_value(frag),
 							fi->next_offset, true);

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[PATCH 4.9 00/41] 4.9.37-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.9 02/41] fs: completely ignore unknown open flags Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.9 01/41] fs: add a VALID_OPEN_FLAGS Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.9 03/41] driver core: platform: fix race condition with driver_override Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.9 05/41] tracing/kprobes: Allow to create probe with a module name starting with a digit Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.9 19/41] pinctrl: sh-pfc: r8a7794: Swap ATA signals Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.9 04/41] ceph: choose readdir frag based on previous readdir reply Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.9 08/41] usb: dwc3: replace %p with %pK Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  Re: [PATCH 4.9 00/41] 4.9.37-stable review Krister Johansen <kjlx@templeofstupid.com> - 2017-07-11 00:40 +0200
    Re: [PATCH 4.9 00/41] 4.9.37-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-11 12:00 +0200
  Re: [PATCH 4.9 00/41] 4.9.37-stable review Guenter Roeck <linux@roeck-us.net> - 2017-07-11 02:50 +0200
  Re: [PATCH 4.9 00/41] 4.9.37-stable review Sumit Semwal <sumit.semwal@linaro.org> - 2017-07-11 12:00 +0200
    Re: [PATCH 4.9 00/41] 4.9.37-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-11 12:40 +0200

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