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    Subject[patch 46/46] fs: sys_sync fix
    2.6.28-stable review patch.  If anyone has any objections, please let us know.

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

    From: Nick Piggin <npiggin@suse.de>

    commit 856bf4d717feb8c55d4e2f817b71ebb70cfbc67b upstream.

    s_syncing livelock avoidance was breaking data integrity guarantee of
    sys_sync, by allowing sys_sync to skip writing or waiting for superblocks
    if there is a concurrent sys_sync happening.

    This livelock avoidance is much less important now that we don't have the
    get_super_to_sync() call after every sb that we sync. This was replaced
    by __put_super_and_need_restart.

    Signed-off-by: Nick Piggin <npiggin@suse.de>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/fs-writeback.c | 20 +-------------------
    include/linux/fs.h | 1 -
    2 files changed, 1 insertion(+), 20 deletions(-)

    --- a/fs/fs-writeback.c
    +++ b/fs/fs-writeback.c
    @@ -652,18 +652,6 @@ void sync_inodes_sb(struct super_block *
    sync_sb_inodes(sb, &wbc);
    }

    -/*
    - * Rather lame livelock avoidance.
    - */
    -static void set_sb_syncing(int val)
    -{
    - struct super_block *sb;
    - spin_lock(&sb_lock);
    - list_for_each_entry_reverse(sb, &super_blocks, s_list)
    - sb->s_syncing = val;
    - spin_unlock(&sb_lock);
    -}
    -
    /**
    * sync_inodes - writes all inodes to disk
    * @wait: wait for completion
    @@ -690,9 +678,6 @@ static void __sync_inodes(int wait)
    spin_lock(&sb_lock);
    restart:
    list_for_each_entry(sb, &super_blocks, s_list) {
    - if (sb->s_syncing)
    - continue;
    - sb->s_syncing = 1;
    sb->s_count++;
    spin_unlock(&sb_lock);
    down_read(&sb->s_umount);
    @@ -710,13 +695,10 @@ restart:

    void sync_inodes(int wait)
    {
    - set_sb_syncing(0);
    __sync_inodes(0);

    - if (wait) {
    - set_sb_syncing(0);
    + if (wait)
    __sync_inodes(1);
    - }
    }

    /**
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -1124,7 +1124,6 @@ struct super_block {
    struct rw_semaphore s_umount;
    struct mutex s_lock;
    int s_count;
    - int s_syncing;
    int s_need_sync_fs;
    atomic_t s_active;
    #ifdef CONFIG_SECURITY


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