On Fri, Feb 13, 2015 at 05:17:10PM +0100, Miroslav Benes wrote: > On Fri, 13 Feb 2015, Josh Poimboeuf wrote: > > Hm, even with Jiri Slaby's suggested fix to add the completion to the > > unregister path, I still get a lockdep warning. This looks more insidious, > > related to the locking order of a kernfs lock and the klp lock. I'll need to > > look at this some more... > > Yes, I was afraid of this. Lockdep warning is a separate bug. It is caused > by taking klp_mutex in enabled_store. During rmmod klp_unregister_patch > takes klp_mutex and destroys the sysfs structure. If somebody writes to > enabled just after unregister takes the mutex and before the sysfs > removal, he would cause the deadlock, because enabled_store takes the > "sysfs lock" and then klp_mutex. That is exactly what the lockdep tells us > below. > > We can look for inspiration elsewhere. Grep for s_active through git log > of the mainline offers several commits which dealt exactly with this. Will > browse through that... Thanks Miroslav, please let me know what you find. It wouldn't surprise me if this were a very common problem. One option would be to move the enabled_store() work out to a workqueue or something. > > > > To recreate: > > > > insmod livepatch-sample.ko > > > > # wait for patching to complete > > > > ~/a.out & <-- simple program which opens the "enabled" file in the background > > I didn't even need such a program. Lockdep warned me with sole insmod, > echo and rmmod. It is magically clever. Ah, even easier... lockdep is awesome. -- Josh -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
