* Re: Poll CQ syncing problem
[not found] ` <3ba1baab-e2ac-358d-3b3b-ff4a27405c93@mellanox.com>
@ 2017-03-01 14:51 ` Christoph Hellwig
2017-03-01 15:28 ` Noa Osherovich
0 siblings, 1 reply; 2+ messages in thread
From: Christoph Hellwig @ 2017-03-01 14:51 UTC (permalink / raw)
To: Noa Osherovich; +Cc: hch, sagi, linux-rdma, Majd Dibbiny, tj, linux-kernel
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?
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Poll CQ syncing problem
2017-03-01 14:51 ` Poll CQ syncing problem Christoph Hellwig
@ 2017-03-01 15:28 ` Noa Osherovich
0 siblings, 0 replies; 2+ messages in thread
From: Noa Osherovich @ 2017-03-01 15:28 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: sagi, linux-rdma, Majd Dibbiny, tj, linux-kernel
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.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2017-03-01 14:51 ` Poll CQ syncing problem Christoph Hellwig
2017-03-01 15:28 ` Noa Osherovich
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