Re: VM deadlock

[Andrew Morton <andrewm@uow.edu.au>]

Chris Mason wrote:
> 
> On Thursday, June 28, 2001 01:21:28 PM +1000 Andrew Morton
> <andrewm@uow.edu.au> wrote:
> ...
> > reiserfs_mark_inode_dirty() has taken a copy of the in-core inode, so
> > it can do this:
> >
> >             spin_lock(&inode_lock);
> >             if ((inode->i_state & I_LOCK) == 0)
> >                     inode->i_state &= ~(I_DIRTY_SYNC|I_DIRTY_DATASYNC);
> >             spin_unlock(&inode_lock);
> >
> > Unfortunately there is no API function to do this, so inode_lock
> > needs to be exported :(
> 
> Well, this is kind of my own fault.  I didn't want the dirty_inode call
> back to be able to screw with the internals of how inode.c dealt with
> things, I wanted it purely to allow actions in addition to what inode.c
> wanted to do.
> 
> So, mark_inode_dirty calls dirty_inode, and then it sets whatever dirty
> bits it wants to.  Clearing them in your own dirty_inode call won't matter,
> they should just get set again later.

yes, the above code is a bit of a waste of space :)

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.

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.

mark_inode_dirty() is the only way in which those bits can get
set. So the risk we face is that someone calls mark_inode_dirty(),
then alters the inode, then there is a call to write_inode().
That would be a bug, IMO.

As for knfsd, well, someone must have called mark_inode_dirty()
at sometime, else they'd never get written.

It's all rather dodgy.

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