Re: Poll CQ syncing problem

[Noa Osherovich]

On 3/1/2017 4:51 PM, Christoph Hellwig wrote:

> On Wed, Mar 01, 2017 at 04:30:26PM +0200, Noa Osherovich wrote:
>> Analysis:
>> Since ib_comp_wq isn't single threaded, two works can run in parallel for the same CQ,
>> executing __ib_process_cq.
> They shouldn't.  Each CQ has a single work_struct, and any given work_struct
> should only be executing at once:
>
> "Note that the flag ``WQ_NON_REENTRANT`` no longer exists as all
> workqueues are now non-reentrant - any work item is guaranteed to be
> executed by at most one worker system-wide at any given time."
>
>> Since this function isn't thread safe and the wc array is shared, it causes a data corruption
>> which eventually crashes in the MAD layer due to a double list_del of the same element.
> This should not be the case.  What kernel version are you testing and does
> it contain any patches touching core kernel code?

Thanks Christoph for the quick response.

Currently we see this only in old kernels. I'll investigate this more and update.