Re: [PATCH] sym53c8xx_2: Avoid calling __sym_mfree with irqs disabled

[Stefan Bader <stefan.bader@canonical.com>]

Matthew Wilcox wrote:
> On Thu, Mar 25, 2010 at 11:21:17AM -0600, James Bottomley wrote:
>> On Thu, 2010-03-25 at 18:05 +0100, Stefan Bader wrote:
>>> The following patch was tested and seemed to avoid the warning. Howver
>>> I am not completely sure that none of the later functions need to be
>>> protected with spinlocks. Though it feels ok. But maybe someone can do
>>> some sanity checking.
>> So, I'm afraid you're right, the patch as is won't work ... the problem
>> is that __sym_mfree_dma does list manipulation and for safety that has
>> to be under a lock.
>>
>> The inception of this problem is that ARM needs a sleeping function on
>> DMA free but nothing else does so, on every platform that sym2 is
>> supported, this warning is bogus.
> 
> Oh good, I'm glad you wrote this, it saves me the typing ;-)
> 
>> One way of getting rid of it might be to undef SYM_MEM_FREE_UNUSED which
>> will prevent the free routines actually from releasing memory ...
>> another might be to drop the lock and reacquire it around the free ...
>> but that's sitting in a list traversal function so it may expose us to
>> list races again, so really the whole of the freeing routines would have
>> to be re-written to be list safe under lock ...
> 
> The solution I'd suggest is to take out the WARN_ON in the x86 code.
> It's never going to cause trouble on x86.

Ok, thanks for the infos. Sounds like this is the quickest solution to a problem
which is not a real one for x86. Maybe limit it to just ARM if that's the only
architecture that has problems with it.

Stefan

> The real solution is to use DMA pools, but my supply of tuits is quite
> limited these days, and converting sym2 to modern APIs isn't high on
> my priority list.
>