* Andrew Morton <[email protected]> wrote:
> btw, I was looking at this change:
> @@ -1003,6 +1003,7 @@ unsigned ata_exec_internal(struct ata_de
> unsigned int err_mask;
> int rc;
>
> + init_completion(&wait);
> spin_lock_irqsave(ap->lock, flags);
>
> /* no internal command while frozen */
>
> That local was already initialised with DEFINE_COMPLETION(). Am
> surprised that an init_completion() also was needed?
That's a fundamental problem of DECLARE_COMPLETION() done on the kernel
stack - it does build-time initialization with no opportunity to inject
any runtime logic. (which lockdep would need. Maybe i missed some clever
way to add a runtime callback into the initialization? [*])
Btw., there is no danger from missing the initialization of a wait
structure: lockdep will detect "uninitialized" on-stack locks and will
complain about it and turn itself off. [this happened a few times during
development - that's how those init_completion() calls got added]
But at a minimum these initializations need to become lockdep-specific
key-reinits - otherwise there will be impact to non-lockdep kernels too.
Ingo
[*] the only solution i can see is to introduce
DECLARE_COMPLETION_ONSTACK(), which could call a function with &wait
passed in, where that function would return with a structure. The macro
magic would resolve to something like:
struct completion wait = lockdep_init_completion(&wait);
and thus the structure would be initialized. But this method cannot be
used for static scope uses of DECLARE_COMPLETION, because it's not a
constant initializer. So we'd definitely have to make a distinction in
terms of _ONSTACK(). Is there really no compiler feature that could help
us out here?
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