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[PATCH 3.10 08/80] dm thin metadata: fix bug when taking a metadata snapshot

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

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

From: Joe Thornber <ejt@redhat.com>

commit 49e99fc717f624aa75ca755d6e7bc029efd3f0e9 upstream.

When you take a metadata snapshot the btree roots for the mapping and
details tree need to have their reference counts incremented so they
persist for the lifetime of the metadata snap.

The roots being incremented were those currently written in the
superblock, which could possibly be out of date if concurrent IO is
triggering new mappings, breaking of sharing, etc.

Fix this by performing a commit with the metadata lock held while taking
a metadata snapshot.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/dm-thin-metadata.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -1191,6 +1191,12 @@ static int __reserve_metadata_snap(struc
 	dm_block_t held_root;
 
 	/*
+	 * We commit to ensure the btree roots which we increment in a
+	 * moment are up to date.
+	 */
+	__commit_transaction(pmd);
+
+	/*
 	 * Copy the superblock.
 	 */
 	dm_sm_inc_block(pmd->metadata_sm, THIN_SUPERBLOCK_LOCATION);

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[PATCH 3.10 00/80] 3.10.99-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 08/80] dm thin metadata: fix bug when taking a metadata snapshot Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 02/80] drm/ast: Initialized data needed to map fbdev memory Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 23/80] dts: vt8500: Add SDHC node to DTS file for WM8650 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 07/80] efi: Disable interrupts around EFI calls, not in the epilog/prolog calls Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 31/80] mac: validate mac_partition is within sector Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 14/80] proc: Fix ptrace-based permission checks for accessing task maps Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 29/80] megaraid_sas : SMAP restriction--do not access user memory from IOCTL code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 32/80] ARC: dw2 unwind: Remove falllback linear search thru FDE entries Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 11/80] USB: cp210x: add IDs for GE B650V3 and B850V3 boards Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 41/80] dm btree: fix bufio buffer leaks in dm_btree_del() error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 27/80] wm831x_power: Use IRQF_ONESHOT to request threaded IRQs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 10/80] can: ems_usb: Fix possible tx overflow Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 01/80] tracepoints: Do not trace when cpu is offline Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 06/80] drm/radeon: fix hotplug race at startup Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 26/80] devres: fix a for loop bounds check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 30/80] mmc: remove bondage between REQ_META and reliable write Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 15/80] iw_cxgb3: Fix incorrectly returning error on success Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 35/80] virtio: fix memory leak of virtio ida cache layers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:40 +0100
  [PATCH 3.10 04/80] bcache: unregister reboot notifier if bcache fails to unregister device Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 03:50 +0100
  Re: [PATCH 3.10 00/80] 3.10.99-stable review Guenter Roeck <linux@roeck-us.net> - 2016-03-02 15:40 +0100
    Re: [PATCH 3.10 00/80] 3.10.99-stable review Willy Tarreau <w@1wt.eu> - 2016-03-02 16:50 +0100
      Re: [PATCH 3.10 00/80] 3.10.99-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-02 18:30 +0100

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