Re: [PATCH] lockdep: Check if nested lock is actually held

From: Maarten Lankhorst
Date: Thu Sep 13 2012 - 06:10:06 EST


Op 13-09-12 11:59, Peter Zijlstra schreef:
> On Thu, 2012-09-13 at 11:39 +0200, Maarten Lankhorst wrote:
>> It is considered good form to lock the lock you claim to be nested in.
> Uhm yeah.. cute. You actually found a site where this triggered?
Not in mainline, I was working on some lockdep annotations for my work on
moving ttm reservations to base kernel, and I wrote a whole bunch of tests
to stress interaction between reservations and locks, one of the tests I
was doing was taking a spinlock without the nested object:

static void reservation_test_fence_nest_unreserved(void)
struct reservation_object o;


spin_lock_nest_lock(&o.fence_lock, &o);

I would have expected it to fail, and the patch fixed it. As a nice side effect
it also complained about another hack I was doing elsewhere with reservations to
tests for deadlocks, and it forced me to fix it in a slightly less hacky way.


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