On Fri, Feb 20, 2015 at 03:07:31PM -0800, Andrew Morton wrote: > - It no longer "acquires a reference". All it does is to acquire an rwsem. > > - What the heck is a "passive reference" anyway? It appears to be > the situation where we increment s_count without incrementing s_active.
Reference to struct super_block that guarantees only that its memory won't be freed until we drop it. > After your patch, this superblock state no longer exists(?), Yes, it does. The _only_ reason why that patch isn't outright bogus is that we do only down_read_trylock() on ->s_umount - try to pull off the same thing with down_read() and you'll get a nasty race. Take a look at e.g. get_super(). Or user_get_super(). Or iterate_supers()/iterate_supers_type(), where we don't return such references, but pass them to a callback instead. In all those cases we end up with passive reference taken, ->s_umount taken shared (_NOT_ with trylock) and fs checked for being still alive. Then it's guaranteed to stay alive until we do drop_super(). I agree that the name blows, BTW - something like try_get_super() might have been more descriptive, but with this change it actually becomes a bad name as well, since after it we need a different way to release the obtained ref; not the same as after get_super(). Your variant might be OK, but I'd probably make it trylock_super(), to match the verb-object order of the rest of identifiers in that area... > so > perhaps the entire "passive reference" concept and any references to > it can be expunged from the kernel. Nope. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
