New subject: [Bug 1025070] btrfs: Continue write in case of can_not_nocow

13 Feb 2017

      http://bugzilla.suse.com/show_bug.cgi?id=1025070

            Bug ID: 1025070
           Summary: btrfs: Continue write in case of can_not_nocow
    Classification: openSUSE
           Product: openSUSE Distribution
           Version: Leap 42.1
          Hardware: Other
                OS: Other
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: Kernel
          Assignee: jeffm@suse.com
          Reporter: jeffm@suse.com
        QA Contact: qa-bugs@suse.de
          Found By: ---
           Blocker: ---

From: Zhao Lei 
Date: Wed, 6 Jan 2016 18:24:43 +0800
Subject: btrfs: Continue write in case of can_not_nocow
Git-commit: 4da2e26a2a32b174878744bd0f07db180c875f26
Patch-mainline: v4.6-rc2
References: pulled from 4.4-stable (4.1-stable had expired)

btrfs failed in xfstests btrfs/080 with -o nodatacow.

Can be reproduced by following script:
  DEV=/dev/vdg
  MNT=/mnt/tmp

  umount $DEV &>/dev/null
  mkfs.btrfs -f $DEV
  mount -o nodatacow $DEV $MNT

  dd if=/dev/zero of=$MNT/test bs=1 count=2048 &
  btrfs subvolume snapshot -r $MNT $MNT/test_snap &
  wait
  --
  We can see dd failed on NO_SPACE.

Reason:
  __btrfs_buffered_write should run cow write when no_cow impossible,
  and current code is designed with above logic.
  But check_can_nocow() have 2 type of return value(0 and <0) on
  can_not_no_cow, and current code only continue write on first case,
  the second case happened in doing subvolume.

Fix:
  Continue write when check_can_nocow() return 0 and <0.

Reviewed-by: Filipe Manana 
Signed-off-by: Zhao Lei 
Acked-by: Jeff Mahoney 
---
 fs/btrfs/file.c | 37 +++++++++++++++++--------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

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[Bug 1025070] New: btrfs: Continue write in case of can_not_nocow

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