Re: [PATCH] staging: ion: WARN when the handle kmap_cnt is going to wrap around

[Mitchel Humpherys]

++greg-kh and devel@xxxxxxxxxxxxxxxxxxxx
(my bad for missing you the first time around)

On Thu, May 22 2014 at 06:09:11 PM, Colin Cross <ccross@xxxxxxxxxxx> wrote:
> On Thu, May 22, 2014 at 5:51 PM, Mitchel Humpherys
> <mitchelh@xxxxxxxxxxxxxx> wrote:
>> There are certain client bugs (double unmap, for example) that can cause
>> the handle->kmap_cnt (an unsigned int) to wrap around from zero. This
>> causes problems when the handle is destroyed because we have:
>>
>>         while (handle->kmap_cnt)
>>                 ion_handle_kmap_put(handle);
>>
>> which takes a long time to complete when kmap_cnt starts at ~0 and can
>> result in a watchdog timeout.
>>
>> WARN and bail when kmap_cnt is about to wrap around from zero.
>>
>> Signed-off-by: Mitchel Humpherys <mitchelh@xxxxxxxxxxxxxx>
>> ---
>>  drivers/staging/android/ion/ion.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
>> index 3d5bf14722..f55f61a4cc 100644
>> --- a/drivers/staging/android/ion/ion.c
>> +++ b/drivers/staging/android/ion/ion.c
>> @@ -626,6 +626,10 @@ static void ion_handle_kmap_put(struct ion_handle *handle)
>>  {
>>         struct ion_buffer *buffer = handle->buffer;
>>
>> +       if (!handle->kmap_cnt) {
>> +               WARN(1, "%s: Double unmap detected! bailing...\n", __func__);
>> +               return;
>> +       }
>>         handle->kmap_cnt--;
>>         if (!handle->kmap_cnt)
>>                 ion_buffer_kmap_put(buffer);
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>> hosted by The Linux Foundation
>>
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>
> Acked-by: Colin Cross <ccross@xxxxxxxxxxx>

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