Re: VM deadlock

[Chris Mason <mason@suse.com>]

On Friday, June 29, 2001 12:08:37 AM +1000 Andrew Morton
<andrewm@uow.edu.au> wrote:

> The reason ->write_inode() can be a no-op is that __sync_one()
> marks the inode clean, then calls ->write_inode().  We *know*
> that we took a copy of the inode in mark_inode_dirty(), so
> we don't need to do anything.

Yes, the only exception is that write_inode needs to honor the sync flag,
at least when not called under PF_MEMALLOC.  The biggest reason I can find
so far is knfsd, who calls write_inode_now and expects the inode to be
securely on disk.  It doesn't call mark_inode_dirty directly, it calls some
FS func (link, create, whatever) and then uses write_inode_now to commit.

> 
> Of course this absolutely requires all inode dirtiers to
> call mark_inode_dirty() after doing the dirty, which is a risk.
> But we face that risk with the PF_MEMALLOC case anyway.  No
> problems have appeared in testing.

I haven't seen any problems caused by it yet, but that might be because
reiserfs does all the important inode writes on its own.  I believe
generic_commit_write is the only place outside the FS that calls
mark_inode_dirty with something other than an atime update.

-chris