Re: [RFC PATCH] staging, android, ashmem: invalidate pin/unpin ioctlfor private map

[JoonSoo Kim]

Hello, Dan.

2012/12/2 Dan Carpenter <dan.carpenter@xxxxxxxxxx>:
> On Sat, Dec 01, 2012 at 02:45:57AM +0900, Joonsoo Kim wrote:
>> @@ -614,21 +616,35 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
>>       pgstart = pin.offset / PAGE_SIZE;
>>       pgend = pgstart + (pin.len / PAGE_SIZE) - 1;
>>
>> -     mutex_lock(&ashmem_mutex);
>> +     if (asma->shared_mapping) {
>> +             mutex_lock(&ashmem_mutex);
>
> Wouldn't we need to hold the mutex while we check the
> ->shared_mapping?

I doesn't fully understand ashmem's lock semantic.
Code for retrieving some value of asma instance doesn't hold the mutex, now.
For example, in ashmem_ioctl(), asma->size, asma->prot_mask.
And in ashmem_pin_unpin(), there is asma->file, asma->size which is
retrieved without the mutex.
According to this semantic, the mutex doesn't need for checking
asma->shared_mapping.

Thanks for review!
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