lkml.org 
[lkml]   [2008]   [Jul]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH 12/15] driver core: Implement tagged directory support for device classes.
    Tejun Heo <htejun@gmail.com> writes:
    >> To do that I believe we would need to ensure sysfs does not use
    >> the inode->i_mutex lock except to keep the VFS layer out. Allowing us
    >> to safely change the directory structure, without holding it.
    >
    > I don't think sysfs is depending on i_mutex anymore but I need to go
    > through the code to make sure.

    The vfs still does. So at least for directory tree manipulation we
    need to hold i_mutex before we grab sysfs_mutex.

    I think that means we need to unscramble the whole set of locking
    order issues.

    In lookup we have:
    local_vfs_lock -> fs_global_lock

    In modifications we have:
    fs_global_lock -> local_vfs_lock

    Which is the definition of a lock ordering problem.

    Currently we play jump through some significant hoops to keep things
    in local_vfs_lock -> fs_global_lock order.

    If we also take the rename_mutex on directory adds and deletes we
    may be able to keep jumping through those hoops. However I expect
    we would be in a much better situation if we could figure out how
    to avoid the problem.

    It looks like the easy way to handle this is to make the sysfs_dirent
    list rcu protected. Which means we can fix our lock ordering problem
    without VFS modifications. Allowing the locking to always
    be: sysfs_mutex ... i_mutex.

    After that it would be safe and a good idea to have unshared
    inodes between superblocks, just so we don't surprise anyone
    making generic VFS assumptions.

    Eric


    \
     
     \ /
      Last update: 2008-07-16 23:15    [W:3.983 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site