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    SubjectRe: inode->i_wb_list corruption.
    On Tue, Mar 06, 2012 at 10:03:07PM +0100, Jan Kara wrote:
    > On Tue 06-03-12 13:51:37, Dave Jones wrote:
    > > We've had three separate reports against 3.2.x recently where the linked list debugging
    > > is getting tripped up by the prev->next pointer being null instead of pointing
    > > to the current list entry while walking the i_wb_list
    > >
    > > Call traces are slightly different each time, but all end up walking i_wb_list
    > > in dput -> d_kill -> i_put -> evict -> inode_wb_list_del
    > >
    > > What protects that list ? It looks to be just bdi->wb.list_lock ?
    > >
    > >
    > > full reports at:
    > > https://bugzilla.redhat.com/show_bug.cgi?id=784741
    > > https://bugzilla.redhat.com/show_bug.cgi?id=799229
    > > https://bugzilla.redhat.com/show_bug.cgi?id=799692
    > Hum, interesting! I'd guess this might be caused by f758eeab - adding
    > Fengguang and Christoph to CC. But I'm really failing to see how this could
    > happen but interesting thing is that in two of the three cases the files
    > are on virtual filesystems (once cgroup, once sysfs). These both use
    > noop_backing_dev_info.

    sysfs/cgroup forgot to init inode->i_wb_list?

    This simplified fix inits it in inode_init_always().

    The better fix would be to add init_once to sysfs or perhaps fix
    sysfs_get_inode()/cgroup_new_inode().

    Thanks,
    Fengguang

    ---
    fs/inode.c | 1 +
    1 file changed, 1 insertion(+)

    --- linux.orig/fs/inode.c 2012-02-22 19:20:48.374799955 -0800
    +++ linux/fs/inode.c 2012-03-06 23:11:29.133899478 -0800
    @@ -193,6 +193,7 @@ int inode_init_always(struct super_block
    inode->i_private = NULL;
    inode->i_mapping = mapping;
    INIT_LIST_HEAD(&inode->i_dentry); /* buggered by rcu freeing */
    + INIT_LIST_HEAD(&inode->i_wb_list);
    #ifdef CONFIG_FS_POSIX_ACL
    inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED;
    #endif

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