linux-kernel - Re: [net-next v3 05/15] net: cavium/liquidio: Convert tasklet API to new bottom half workqueue mechanism

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Message-ID: <CAOMdWSLEWzdzSEzZqhZAMqfG7OtpLPeFGMuUVn1eYt1Pc_YhRA@mail.gmail.com>
Date: Thu, 15 Aug 2024 09:45:43 -0700
From: Allen <allen.lkml@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, jes@...ined-monkey.org, kda@...ux-powerpc.org, 
	cai.huoqing@...ux.dev, dougmill@...ux.ibm.com, npiggin@...il.com, 
	christophe.leroy@...roup.eu, aneesh.kumar@...nel.org, 
	naveen.n.rao@...ux.ibm.com, nnac123@...ux.ibm.com, tlfalcon@...ux.ibm.com, 
	cooldavid@...ldavid.org, marcin.s.wojtas@...il.com, mlindner@...vell.com, 
	stephen@...workplumber.org, nbd@....name, sean.wang@...iatek.com, 
	Mark-MC.Lee@...iatek.com, lorenzo@...nel.org, matthias.bgg@...il.com, 
	angelogioacchino.delregno@...labora.com, borisp@...dia.com, 
	bryan.whitehead@...rochip.com, UNGLinuxDriver@...rochip.com, 
	louis.peens@...igine.com, richardcochran@...il.com, 
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-acenic@...site.dk, linux-net-drivers@....com, netdev@...r.kernel.org, 
	Sunil Goutham <sgoutham@...vell.com>
Subject: Re: [net-next v3 05/15] net: cavium/liquidio: Convert tasklet API to
 new bottom half workqueue mechanism

> > > > In the context of of the driver, the conversion from tasklet_enable()
> > > > to enable_and_queue_work() is correct because the callback function
> > > > associated with the work item is designed to be safe even if there
> > > > is no immediate work to process. The callback function can handle
> > > > being invoked in such situations without causing errors or undesirable
> > > > behavior. This makes the workqueue approach a suitable and safe
> > > > replacement for the current tasklet mechanism, as it provides the
> > > > necessary flexibility and ensures that the work item is properly
> > > > scheduled and executed.
> > >
> > > Fewer words, clearer indication that you read the code would be better
> > > for the reviewer. Like actually call out what in the code makes it safe.
> > >
> > Okay.
> > > Just to be clear -- conversions to enable_and_queue_work() will require
> > > manual inspection in every case.
> >
> > Attempting again.
> >
> > The enable_and_queue_work() only schedules work if it is not already
> > enabled, similar to how tasklet_enable() would only allow a tasklet to run
> > if it had been previously scheduled.
> >
> > In the current driver, where we are attempting conversion, enable_work()
> > checks whether the work is already enabled and only enables it if it
> > was disabled. If no new work is queued, queue_work() won't be called.
> > Hence, the callback is safe even if there's no work.
>
> Hm. Let me give you an example of what I was hoping to see for this
> patch (in addition to your explanation of the API difference):
>
>  The conversion for oct_priv->droq_bh_work should be safe. While
>  the work is per adapter, the callback (octeon_droq_bh()) walks all
>  queues, and for each queue checks whether the oct->io_qmask.oq mask
>  has a bit set. In case of spurious scheduling of the work - none of
>  the bits should be set, making the callback a noop.

Thank you. Really appreciate your patience and help.

Would you prefer a new series/or update this patch with this
additional info and resend it.

Thanks.

-- 
       - Allen