On Tue, Sep 23, 2014 at 11:38:59PM +1000, Dave Chinner wrote: That way would certainly require fewer changes. But it seemed to me like adding a pair of hooks that only gfs2 needed would have less support. If people would prefer a patch like that, I can easily change it. thanks. -Ben > On Mon, Sep 22, 2014 at 09:06:41PM -0500, Benjamin Marzinski wrote: > > Currently, freezing a filesystem involves calling freeze_super, which locks > > sb->s_umount and then calls the fs-specific freeze_fs hook. This makes it > > hard for gfs2 (and potentially other cluster filesystems) to use the vfs > > freezing code to do freezes on all the cluster nodes. > > > > In order to communicate that a freeze has been requested, and to make sure > > that only one node is trying to freeze at a time, gfs2 uses a glock > > (sd_freeze_gl). The problem is that there is no hook for gfs2 to acquire > > this lock before calling freeze_super. This means that two nodes can > > attempt to freeze the filesystem by both calling freeze_super, acquiring > > the sb->s_umount lock, and then attempting to grab the cluster glock > > sd_freeze_gl. Only one will succeed, and the other will be stuck in > > freeze_super, making it impossible to finish freezing the node. > > > > To solve this problem, this patch pushes the freeze/unfreeze_fs hooks to > > before freeze/thaw_super, and makes freeze/thaw_super take a callback > > function to execute any fs specific code that needs to be done while > > s_umount is held. This also means that every filesystem that implements > > freeze/unfreeze_fs must call freeze/thaw_super from that function. > > Wouldn't just adding a ->prepare_freeze/->prepare_thaw method pair > and adding gfs2 cluster locking to those new methods be better? > That way no other filesystem code needs to change at all... > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
