Re: bus_dmamap_destroy no longer callable from interrupt context?

[Lars Heidieker <lars%heidieker.de@localhost>]

On 11/15/2013 05:57 PM, Matt Thomas wrote:
> 
> On Nov 15, 2013, at 6:22 AM, Christoph Badura <bad%bsd.de@localhost> wrote:
> 
>> While trying to port BCM586x support I discovered that I get the following
>> panic under -current.  The same code works fine on -6.  What gives?
>>
>> panic: kernel diagnostic assertion "((!cpu_intr_p() && !cpu_softintr_p()) || 
>> (pc->pc_pool.pr_ipl != IPL_NONE || cold || panicstr != NULL)" failed: file 
>> "../../../../kern/subr_pool.c", line 2209 pool 'vmmpepl' is IPL_NONE, but 
>> called from interrupt context
>>
>> backtrace:
>> ...
>> kern_assert
>> pool_cache_get_paddr
>> _uvm_mapent_alloc.clone.2
>> uvm_map_dup_start
>> uvm_unmap_remove
>> uvm_unmap1
>> _bus_dmamap_destroy_clone.8
>> ubsec_callback+0x9d
>> ubsec_intr+0x100
>> intr_biglock_wrapper
>> ...
>>
>> This is generic ubsec code that is used by our currently supported devices.
>> I.e. ubsec(4) should be completely busted.
> 
> it's intentional.  dmamap create/destroy can't be done from interrupt because 
> they allocate memory.  besides mbufs, memory can't be allocated.  I don't 
> agree with the softintr restriction (where else can drivers allocate).
> 

Matt, you mean allocating and freeing memory from softint context should
be ok? That's something that went through my mind as well and I think
it's the right way.
Having special pools for those allocations, which aren't special in any
other sense then allocating and freeing happens from interrupt context,
doesn't make sense, the backing for the pools needs to be safe anyway.
Allowing those allocation from softint context would simplify this.
I don't think there are many code paths that do allocations from
hardware interrupts and those should get rewritten to either do
allocation from thread or softint context, preferable from thread context.

Just my thoughts,
Lars


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