How to get a global state of the locks in Linux kernel?

Question

I'm writing some code for the Linux kernel and I noticed the interrupts are disabled when I need them to be enabled so that a process can handle a signal. It would be fantastic if I could just obtain a list of all the locks currently being hold in the system, as my suspicion is that a lock somewhere has disabled interruptions... This is, assuming that it was a lock that disabled the interruptions. If not, it would also be nice to know how did so (or where). Does the Linux kernel keep any record of this?

Answer 1

Yes, the kernel definitely has the ability to keep track of currently held locks, but that's costly and only done for debugging purposes. You should configure and compile your kernel with debugging enabled (specifically CONFIG_LOCKDEP , which also depends on other config options).

Once that is done, in struct task_struct there are various fields such as lockdep_depth (number of currently held locks) and held_locks (array of struct held_lock representing currently held locks) that could be useful for you. You could check those fields for the current task when your module is running to find out what is going on.

Take a look at the two private functions lockdep_print_held_locks() and print_lock() from kernel/locking/lockdep.c to see how to extract useful information from those struct held_lock . You could also use the kgdb kernel debugger in order to look specifically at what is happening when your kernel code runs.