[PATCH v3][for 4.15] dmaengine: dmatest: move callback wait queue to thread context

[Adam Wallis]

On 11/17/2017 10:57 AM, Dan Williams wrote:
> On Fri, Nov 17, 2017 at 7:28 AM, Adam Wallis <awallis at codeaurora.org> wrote:
>> On 11/17/2017 10:12 AM, Dan Williams wrote:
>>> On Fri, Nov 17, 2017 at 6:11 AM, Adam Wallis <awallis at codeaurora.org> wrote:
>>>> Commit adfa543e7314 ("dmatest: don't use set_freezable_with_signal()")
>>>> introduced a bug (that is in fact documented by the patch commit text)
>>>> that leaves behind a dangling pointer. Since the done_wait structure is
>>>> allocated on the stack, future invocations to the DMATEST can produce
>>>> undesirable results (e.g., corrupted spinlocks).
>>>>
>>>> Commit a9df21e34b42 ("dmaengine: dmatest: warn user when dma test times
>>>> out") attempted to WARN the user that the stack was likely corrupted but
>>>> did not fix the actual issue.
>>>>
>>>> This patch fixes the issue by pushing the wait queue and callback
>>>> structs into the the thread structure. If a failure occurs due to time,
>>>> dmaengine_terminate_all will force the callback to safely call
>>>> wake_up_all() without possibility of using a freed pointer.
>>>>
>>>> Cc: stable at vger.kernel.org # 4.13.x: a9df21e: dmatest: Warn User
>>>> Cc: stable at vger.kernel.org # 4.13.x
>>>> Cc: stable at vger.kernel.org # 4.14.x
>>>
>>
>> Sure - do you want me to remove them? I was just following the instructions on
>> stable.
> 
> It's not broken, just a note for next time.
> 
>>
>>> You don't need 3 cc stables, you don't even need the "#
>>> kernel-version". Since you have the "Fixes:" line the target kernel(s)
>>> for the backport can be auto-determined. I should go update
>>> Documentation/process/stable-kernel-rules.rst to mention this.
>>>
>>>> Bug: https://bugzilla.kernel.org/show_bug.cgi?id=197605
>>>> Fixes: adfa543e7314 ("dmatest: don't use set_freezable_with_signal()")
>>>> Reviewed-by: Sinan Kaya <okaya at codeaurora.org>
>>>> Suggested-by: Shunyong Yang <shunyong.yang at hxt-semitech.com>
>>>> Signed-off-by: Adam Wallis <awallis at codeaurora.org>
>>>> ---
>>>> changes from v2: Added "Fixes" tag
>>>> changes from v1: Added pre-req patches for stable
>>>>
>>>>  drivers/dma/dmatest.c | 37 ++++++++++++++++---------------------
>>>>  1 file changed, 16 insertions(+), 21 deletions(-)
>>>>
>>>> diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c
>>>> index 47edc7f..2573b6c 100644
>>>> --- a/drivers/dma/dmatest.c
>>>> +++ b/drivers/dma/dmatest.c
>>>> @@ -155,6 +155,12 @@ struct dmatest_params {
>>>>  #define PATTERN_COUNT_MASK     0x1f
>>>>  #define PATTERN_MEMSET_IDX     0x01
>>>>
>>>> +/* poor man's completion - we want to use wait_event_freezable() on it */
>>>> +struct dmatest_done {
>>>> +       bool                    done;
>>>> +       wait_queue_head_t       *wait;
>>>> +};
>>>> +
>>>>  struct dmatest_thread {
>>>>         struct list_head        node;
>>>>         struct dmatest_info     *info;
>>>> @@ -165,6 +171,8 @@ struct dmatest_thread {
>>>>         u8                      **dsts;
>>>>         u8                      **udsts;
>>>>         enum dma_transaction_type type;
>>>> +       wait_queue_head_t done_wait;
>>>
>>> Why are we defining a waitquehead per thread vs defining one globally
>>> for the whole module with "static DECLARE_WAIT_QUEUE_HEAD(x);"?
>>
>> This is how the original dmatest functions. Each thread had a wait queue that it
>> created so that it could go to sleep while the DMA transfer occurred. Each
>> thread is dependent on its own DMA transaction for the wakeup call. Again, this
>> is how the test originally worked. I just moved the wait queue from the stack
>> (which was getting corrupted) to the thread context to allow for safe cleanup.
>> In other words, I haven't really changed how the test works...just fixing a bug
>> with the current implementation.
> 
> Ok, always takes me a bit to re-orient myself to this file since I
> only look at it once a year.
> 
> This fix seems incomplete. The next test iteration after a timeout
> will now reuse the per-thread 'done' notification. If the engine that
> timed out still completes its dma it will collide with the next
> operation that is using the same 'done' variable. So it seems to me
> that the wait_queue_head should be global, and the 'done' variable
> should be either allocated per-operation or we should call
> dmaengine_terminate_all() after a timeout. Since not all engines
> implement a terminate I think the potential memory leak of a few
> 'done' variables is a better option.
> 
Dan
An important part of my patch was severed in this v3 submission. My apologies.

There is a change that addresses, I believe, your concern that was in v2

 	/* terminate all transfers on specified channels */
-	if (ret)
+	if (ret || failed_tests)
 		dmaengine_terminate_all(chan);

Will clean up again, retest, and resubmit. Thanks for your patience and instruction.

Adam

-- 
Adam Wallis
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.