Re: [RFC PATCH net] ibmvnic: complete dev->poll nicely during adapter reset

Lijun Pan [lijunp213@gmail.com] wrote:

On Fri, Mar 5, 2021 at 12:44 PM Sukadev Bhattiprolu
[off-list ref] wrote:

quoted

Lijun Pan [ljp@linux.ibm.com] wrote:

quoted

The reset path will call ibmvnic_cleanup->ibmvnic_napi_disable
->napi_disable(). This is supposed to stop the polling.
Commit 21ecba6c48f9 ("ibmvnic: Exit polling routine correctly
during adapter reset") reported that the during device reset,
polling routine never completed and napi_disable slept indefinitely.
In order to solve that problem, resetting bit was checked and
napi_complete_done was called before dev->poll::ibmvnic_poll exited.

Checking for resetting bit in dev->poll is racy because resetting
bit may be false while being checked, but turns true immediately
afterwards.

Yes, have been testing a fix for that.

quoted

Hence we call napi_complete in ibmvnic_napi_disable, which avoids
the racing with resetting, and makes sure dev->poll and napi_disalbe

napi_complete() will prevent a new call to ibmvnic_poll() but what if
ibmvnic_poll() is already executing and attempting to access the scrqs
while the reset path is freeing them?

napi_complete() and napi_disable() are called in the earlier stages of
reset path, i.e. before reset path actually calls the functions to
freeing scrqs.

Yes, those will prevent a _new_ call to poll right?

But what if poll is already executing? What prevents it from accessing
an scrq that the reset path will free?

So I don't think this is a issue here.