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

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Message-ID: <20210305184157.GA1411314@us.ibm.com>
Date:   Fri, 5 Mar 2021 10:41:57 -0800
From:   Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
To:     Lijun Pan <ljp@...ux.ibm.com>
Cc:     netdev@...r.kernel.org, kuba@...nel.org, davem@...emloft.net,
        drt@...ux.ibm.com, tlfalcon@...ux.ibm.com
Subject: Re: [RFC PATCH net] ibmvnic: complete dev->poll nicely during
 adapter reset

Lijun Pan [ljp@...ux.ibm.com] wrote:
> 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.
> 
> 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?

Sukadev