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
