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    Subject[PATCH 3.2 132/221] nilfs2: fix deadlock of segment constructor during recovery
    3.2.69-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

    commit 283ee1482f349d6c0c09dfb725db5880afc56813 upstream.

    According to a report from Yuxuan Shui, nilfs2 in kernel 3.19 got stuck
    during recovery at mount time. The code path that caused the deadlock was
    as follows:

    nilfs_fill_super()
    load_nilfs()
    nilfs_salvage_orphan_logs()
    * Do roll-forwarding, attach segment constructor for recovery,
    and kick it.

    nilfs_segctor_thread()
    nilfs_segctor_thread_construct()
    * A lock is held with nilfs_transaction_lock()
    nilfs_segctor_do_construct()
    nilfs_segctor_drop_written_files()
    iput()
    iput_final()
    write_inode_now()
    writeback_single_inode()
    __writeback_single_inode()
    do_writepages()
    nilfs_writepage()
    nilfs_construct_dsync_segment()
    nilfs_transaction_lock() --> deadlock

    This can happen if commit 7ef3ff2fea8b ("nilfs2: fix deadlock of segment
    constructor over I_SYNC flag") is applied and roll-forward recovery was
    performed at mount time. The roll-forward recovery can happen if datasync
    write is done and the file system crashes immediately after that. For
    instance, we can reproduce the issue with the following steps:

    < nilfs2 is mounted on /nilfs (device: /dev/sdb1) >
    # dd if=/dev/zero of=/nilfs/test bs=4k count=1 && sync
    # dd if=/dev/zero of=/nilfs/test conv=notrunc oflag=dsync bs=4k
    count=1 && reboot -nfh
    < the system will immediately reboot >
    # mount -t nilfs2 /dev/sdb1 /nilfs

    The deadlock occurs because iput() can run segment constructor through
    writeback_single_inode() if MS_ACTIVE flag is not set on sb->s_flags. The
    above commit changed segment constructor so that it calls iput()
    asynchronously for inodes with i_nlink == 0, but that change was
    imperfect.

    This fixes the another deadlock by deferring iput() in segment constructor
    even for the case that mount is not finished, that is, for the case that
    MS_ACTIVE flag is not set.

    Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
    Reported-by: Yuxuan Shui <yshuiv7@gmail.com>
    Tested-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/nilfs2/segment.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    --- a/fs/nilfs2/segment.c
    +++ b/fs/nilfs2/segment.c
    @@ -1903,6 +1903,7 @@ static void nilfs_segctor_drop_written_f
    struct the_nilfs *nilfs)
    {
    struct nilfs_inode_info *ii, *n;
    + int during_mount = !(sci->sc_super->s_flags & MS_ACTIVE);
    int defer_iput = false;

    spin_lock(&nilfs->ns_inode_lock);
    @@ -1915,10 +1916,10 @@ static void nilfs_segctor_drop_written_f
    brelse(ii->i_bh);
    ii->i_bh = NULL;
    list_del_init(&ii->i_dirty);
    - if (!ii->vfs_inode.i_nlink) {
    + if (!ii->vfs_inode.i_nlink || during_mount) {
    /*
    - * Defer calling iput() to avoid a deadlock
    - * over I_SYNC flag for inodes with i_nlink == 0
    + * Defer calling iput() to avoid deadlocks if
    + * i_nlink == 0 or mount is not yet finished.
    */
    list_add_tail(&ii->i_dirty, &sci->sc_iput_queue);
    defer_iput = true;


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