Messages in this thread | | | Date | Fri, 12 Jul 2002 15:41:23 -0500 (CDT) | From | Oliver Xymoron <> | Subject | Re: spinlock assertion macros |
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On Fri, 12 Jul 2002, Daniel Phillips wrote:
> On Friday 12 July 2002 14:07, Dave Jones wrote: > > On Thu, Jul 11, 2002 at 09:17:44PM +0200, Daniel Phillips wrote: > > > On Thursday 11 July 2002 20:03, Jesse Barnes wrote: > > > > How about this? > > > > > > It looks good, the obvious thing we don't get is what the actual lock > > > count is, and actually, we don't care because we know what it is in > > > this case. > > > > Something I've been meaning to hack up for a while is some spinlock > > debugging code that adds a FUNCTION_SLEEPS() to (ta-da) functions that > > may sleep. > > Yesss. May I suggest simply SLEEPS()? (Chances are, we know it's a > function.) > > > This macro then checks whether we're currently holding any > > locks, and if so printk's the names of locks held, and where they were taken. > > And then oopes? > > > When I came up with the idea[1] I envisioned some linked-lists frobbing, > > but in more recent times, we can now check the preempt_count for a > > quick-n-dirty implementation (without the additional info of which locks > > we hold, lock-taker, etc). > > Spin_lock just has to store the address/location of the lock in a > per-cpu vector, and the assert prints that out when it oopses. Such > bugs won't live too long under those conditions.
Store it in the task struct, and store a pointer to the previous (outer lock) in that lock, then you've got a linked list of locks per task - very useful. You'll need a helper function - current() is hard to get at from spinlock.h due to tangled dependencies. As I mentioned before, it can also be very handy to stash the address of the code that took the lock in the lock itself.
> Any idea how one might implement NEVER_SLEEPS()? Maybe as: > > NEVER_ [code goes here] _SLEEPS > > which inc/dec the preeempt count, triggering a BUG in schedule().
NEVER_SLEEPS will only trigger on the rare events that blow up anyway, while the MAY_SLEEP version catches _potential_ problems even when the fatal sleep doesn't happen.
-- "Love the dolphins," she advised him. "Write by W.A.S.T.E.."
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