On Tue, Mar 15, 2016 at 07:29:59PM +0530, Chetan Nanda wrote:
On 15-Mar-2016 7:19 pm, "Cihangir Akturk" <cakturk@gmail.com> wrote:
On Thu, Mar 10, 2016 at 02:59:31PM +0530, Chetan Nanda wrote:
Hi,
As per book (Linux kernel development)
"Whoever locked a mutex must unlock it.That is, you cannot lock a mutex
in one
context and then unlock it in another " but 'mutex_unlock' code is not checking the owner field at all.
If you look at the definition of mutex structure in mutex.h:50, you'll see that the owner field will be compiled in if one of CONFIG_DEBUG_MUTEXES or CONFIG_MUTEX_SPIN_ON_OWNER is defined.
And debug_mutex_unlock function in mutex-debug.c:72 will check the owner and emits warning if it finds out that the mutex isn't unlocked by its owner.
http://lxr.free-electrons.com/source/include/linux/mutex.h#L50 http://lxr.free-electrons.com/source/kernel/locking/mutex-debug.c#L72
Thanks for your mail, in my kernel CONFIG_MUTEX_SPIN_ON_OWNER is enabled but CONFIG_DEBUG_MUTEX is not enabled. So there are no warning messages in logs.
I am not an expert but this might be related to debug_locks variable defined in http://lxr.free-electrons.com/source/lib/debug_locks.c#L24
Also, it don't seems to be a real performance hit by adding a single check of owner with current in unlock code.