* Al Viro <[EMAIL PROTECTED]> wrote: > > > So two questions: why isn't -f the default? And is /sys/slab > > > > Because it gives misleading output. It displays the name of the > > first of multiple slabs that share the same storage structures. > > 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. > > 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. > > 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. > > 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.
as a sidenote: bugs like this seem to be reoccuring. People implement sysfs bindings (without being sysfs internals experts - and why should they be) - and create hard to debug problems. We've seen that with the scheduler's recent sysfs changes too. shouldnt the sysfs code be designed in a way to not allow such bugs? The primary usecase of sysfs is by people who do _not_ deal with it on a daily basis. So if they pick APIs that look obvious and create hard to debug problems (and userspace incompatibilities) that's a primary failure of sysfs, not a failure of those who utilize it. At a minimum there should be some _strong_ debugging facility that transparently detects and reports such bugs as they occur. CONFIG_DEBUG_KOBJECT is totally unusable right now, it spams the syslog (so no distro ever enables it - i disable it in random bootups as well because it takes _ages_ to even get to a boot prompt) and never finds any of these hard-to-find-but-easy-to-explain bugs. or if sysfs/kobjects should be scrapped and rewritten, do you have any insight into what kind of abstraction could/should replace it? Should we go back to procfs and get rid of kobjects altogether? (as it's slowly turning into a /proc problem of itself, with worse compatibility and sneakier bugs.) Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/