On Sun, May 18, 2003 at 07:24:17PM +0200, Peter T. Breuer wrote:
> Though I've got quite good at finding and removing deadlocks in my old
> age, there are still two popular ways that the rest of the world's
> prgrammers often shoot themselves in the foot with a spinlock:
>
> a) sleeping while holding the spinlock
> b) taking the spinlock in a subroutine while you already have it
[...]
> The second method is used by programmers who aren't aware that some
> obscure subroutine takes a spinlock, and who recklessly take a lock
> before calling a subroutine (the very thought sends shivers down my
> spine ...).
Recursive spinlocks only hide the problem - consider programmers who take
lock B and recklessly call a subroutine that takes lock A followed be lock
B. The resulting code will appear to work fine, but may have introduced a
subtle AB-BA deadlock. I'd rather have a coding defect that reliably and
consistently causes a deadlock than one that causes deadlocks in rare
timing related cases.
>A popular scenario involves not /knowing/ that your routine
> is called by the kernel with some obscure lock already held, and then
> calling a subroutine that calls the same obscure lock.
If the kernel invokes a callback with an obscure lock held (that is
promiscuous enough to be grabbed in other helper sub-routines), then its
probably a bug - why not just fix it?
-Kevin
-- ------------------------------------------------------------------------ | Kevin O'Connor "BTW, IMHO we need a FAQ for | | kevin@koconnor.net 'IMHO', 'FAQ', 'BTW', etc. !" | ------------------------------------------------------------------------ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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