• Vyacheslav Dubeyko's avatar
    nilfs2: fix issue with flush kernel thread after remount in RO mode because of... · 8c26c4e2
    Vyacheslav Dubeyko authored
    nilfs2: fix issue with flush kernel thread after remount in RO mode because of driver's internal error or metadata corruption
    
    The NILFS2 driver remounts itself in RO mode in the case of discovering
    metadata corruption (for example, discovering a broken bmap).  But
    usually, this takes place when there have been file system operations
    before remounting in RO mode.
    
    Thereby, NILFS2 driver can be in RO mode with presence of dirty pages in
    modified inodes' address spaces.  It results in flush kernel thread's
    infinite trying to flush dirty pages in RO mode.  As a result, it is
    possible to see such side effects as: (1) flush kernel thread occupies
    50% - 99% of CPU time; (2) system can't be shutdowned without manual
    power switch off.
    
    SYMPTOMS:
    (1) System log contains error message: "Remounting filesystem read-only".
    (2) The flush kernel thread occupies 50% - 99% of CPU time.
    (3) The system can't be shutdowned without manual power switch off.
    
    REPRODUCTION PATH:
    (1) Create volume group with name "unencrypted" by means of vgcreate utility.
    (2) Run script (prepared by Anthony Doggett <Anthony2486@interfaces.org.uk>):
    
      ----------------[BEGIN SCRIPT]--------------------
      #!/bin/bash
    
      VG=unencrypted
      #apt-get install nilfs-tools darcs
      lvcreate --size 2G --name ntest $VG
      mkfs.nilfs2 -b 1024 -B 8192 /dev/mapper/$VG-ntest
      mkdir /var/tmp/n
      mkdir /var/tmp/n/ntest
      mount /dev/mapper/$VG-ntest /var/tmp/n/ntest
      mkdir /var/tmp/n/ntest/thedir
      cd /var/tmp/n/ntest/thedir
      sleep 2
      date
      darcs init
      sleep 2
      dmesg|tail -n 5
      date
      darcs whatsnew || true
      date
      sleep 2
      dmesg|tail -n 5
      ----------------[END SCRIPT]--------------------
    
    (3) Try to shutdown the system.
    
    REPRODUCIBILITY: 100%
    
    FIX:
    
    This patch implements checking mount state of NILFS2 driver in
    nilfs_writepage(), nilfs_writepages() and nilfs_mdt_write_page()
    methods.  If it is detected the RO mount state then all dirty pages are
    simply discarded with warning messages is written in system log.
    
    [akpm@linux-foundation.org: fix printk warning]
    Signed-off-by: default avatarVyacheslav Dubeyko <slava@dubeyko.com>
    Acked-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
    Cc: Anthony Doggett <Anthony2486@interfaces.org.uk>
    Cc: ARAI Shun-ichi <hermes@ceres.dti.ne.jp>
    Cc: Piotr Szymaniak <szarpaj@grubelek.pl>
    Cc: Zahid Chowdhury <zahid.chowdhury@starsolutions.com>
    Cc: Elmer Zhang <freeboy6716@gmail.com>
    Cc: Wu Fengguang <fengguang.wu@intel.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    8c26c4e2
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