Re: Major regression on hackbench with SLUB (more numbers)

Christoph Lameter
2007-12-27T05:51:56Z

On Wed, 26 Dec 2007, Al Viro wrote:

> Erm... Let me spell it out: current lifetime rules are completely broken.
> As it is, create/destroy/create cache sequence will do kobject_put() on
> kfree'd object. Even without people playing with holding sysfs files
> open or doing IO on those.

Urgh. Help! Isnt there some sanity with sysfs?

> a) you have kobject embedded into struct with the lifetime rules of its
> own. When its refcount hits zero you kfree() the sucker, even if you
> still have references to embedded kobject.

So alloate it separately?

> b) your symlinks stick around. Even when cache is long gone you still
> have a sysfs symlink with its embedded kobject as a target. They are
> eventually removed when cache with the same name gets created. _Then_
> you get the target kobject dropped - when the memory it used to be in
> had been freed for hell knows how long and reused by something that would
> not appreciate slub.c code suddenly deciding to decrement some word in
> that memory.

Hmmmm.. That would also be addressed by a having a separately allocated
kobject?

> c) you leak references to these kobject; kobject_del() only removes it
> from the tree undoing the effect of kobject_add() and you still need
> kobject_put() to deal with the last reference.

Patches would be appreciated.... Had a hard time to get the sysfs support
to work right.