Re: [PATCH] lockdep: Show address of "struct lockdep_map" at print_lock().

[Michal Hocko <mhocko@kernel.org>]

On Mon 26-03-18 15:19:11, Michal Hocko wrote:
> On Mon 26-03-18 19:18:33, Tetsuo Handa wrote:
> > Currently, print_lock() is printing hlock->acquire_ip field in both
> > "[<%px>]" and "%pS" format. But "[<%px>]" is little useful nowadays, for
> > we use scripts/faddr2line which receives "%pS" for finding the location
> > in the source code.
> > 
> > Since "struct lockdep_map" is embedded into lock objects, we can know
> > which instance of a lock object is acquired using hlock->instance field.
> > This will help finding which threads are causing a lock contention when
> > e.g. the OOM reaper failed to acquire an OOM victim's mmap_sem for read.
> 
> How? All I can see is that we can match which instances are the same.
> This would be an interesting thing to know AFAICS because you can tell
> different instances of lock apart. So the patch makes some sense to me,
> I am just not sure about changelog.

Also, are you sure that %px is appropriate? Can this be abused to leak
the kernel pointer and infere other useful data from it? %p should be
sufficient to tell different lock instances even with the hashed
addresses.
-- 
Michal Hocko
SUSE Labs