linux-kernel - Re: [PATCH 1/2] list: introduce a new cutting helper

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Message-ID: <046f42c5-34b5-41a2-9680-5ef86ef25c01@paulmck-laptop>
Date: Thu, 13 Jun 2024 09:01:47 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Keith Busch <kbusch@...nel.org>
Cc: Nilay Shroff <nilay@...ux.ibm.com>, l@...sch-mbp.dhcp.thefacebook.com,
	Keith Busch <kbusch@...a.com>, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	hch@....de, sagi@...mberg.me, davidgow@...gle.com,
	akpm@...ux-foundation.org, venkat88@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/2] list: introduce a new cutting helper

On Thu, Jun 13, 2024 at 09:40:36AM -0600, Keith Busch wrote:
> On Thu, Jun 13, 2024 at 08:15:06AM -0700, Paul E. McKenney wrote:
> > On Thu, Jun 13, 2024 at 08:47:26AM -0600, Keith Busch wrote:
> > > > 
> > > > Just make a helper function like this:
> > > > 
> > > > 	static void my_synchronize_srcu(void)
> > > > 	{
> > > > 		synchronize_srcu(&my_srcu_struct);
> > > > 	}
> > > > 
> > > > Or am I missing something subtle here?
> > > 
> > > That would work if we had a global srcu, but the intended usage
> > > dynamically allocates one per device the driver is attached to, so a
> > > void callback doesn't know which one to sync.
> > 
> > Ah, good point!  I suppose that a further suggestion to just JIT the
> > needed function would not be well-received?  ;-)
> > 
> > I cannot resist suggesting placing a pointer to the srcu_struct in
> > the task structure.  /me runs...
> > 
> > Perhaps somewhat more constructively, my usual question:  Is it really
> > necessary to have per-driver SRCU here?  What would break if there was
> > a global srcu_struct that applied to all drivers?
> 
> There's not a strict need for srcu_struct to be per device that I know
> of. It was just done this way to keep usage localized to the parts that
> need to be protected. The fear being that one device's long running
> reader could prevent another device from quickly tearing down.

That is a legitimate concern.

Is there a way to avoid this issue by making this be a statement parameter
to a macro?

							Thanx, Paul