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Re: [Cluster-devel] [GFS2 PATCH] GFS2: Increase i_writecount during gfs2_setattr_size



----- Original Message -----
| > --- a/fs/gfs2/rgrp.c
| > +++ b/fs/gfs2/rgrp.c
| > @@ -638,8 +638,10 @@ void gfs2_rs_deltree(struct gfs2_blkreserv *rs)
| >   */
| >  void gfs2_rs_delete(struct gfs2_inode *ip)
| >  {
| > +	struct inode *inode = &ip->i_inode;
| > +
| >  	down_write(&ip->i_rw_mutex);
| > -	if (ip->i_res) {
| > +	if (ip->i_res && atomic_read(&inode->i_writecount) <= 1) {
| >  		gfs2_rs_deltree(ip->i_res);
| >  		BUG_ON(ip->i_res->rs_free);
| >  		kmem_cache_free(gfs2_rsrv_cachep, ip->i_res);
| > 
| 
| Are there any other callers of gfs2_rs_delete where it is no appropriate
| to have this new test?
| 
| I assume that the issue is that this writecount test needs to be under
| the i_rw_mutex?
| 
| Steve.

Hi,

Nope. It's okay for reservations to go in and out of a rgrp reservations tree;
it happens all the time. What we really need to protect is where it's
freed from cache (kmem_cache_free) which only happens in function
gfs2_rs_deltree, where it's now protected by this patch. And yes, it
needs to be done under the i_rw_mutex.

The bigger question is whether there are other places besides functions
gfs2_setattr_size and gfs2_page_mkwrite that should be calling
get_write_access to ensure this protection. These are the only two
we've seen in actual practice, and I wanted the patch to be as
minimal as possible.

Regards,

Bob Peterson
Red Hat File Systems


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