netdev - Re: [PATCH net-next v3 1/6] net: phy: mscc: migrate to phy_select/restore

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Message-ID: <20181119152830.GE26852@lunn.ch>
Date:   Mon, 19 Nov 2018 16:28:30 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Andreas Schwab <schwab@...e.de>
Cc:     Quentin Schulz <quentin.schulz@...tlin.com>, davem@...emloft.net,
        f.fainelli@...il.com, allan.nielsen@...rochip.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        thomas.petazzoni@...tlin.com, alexandre.belloni@...tlin.com,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH net-next v3 1/6] net: phy: mscc: migrate to
 phy_select/restore_page functions

On Mon, Nov 19, 2018 at 04:13:10PM +0100, Andreas Schwab wrote:
> On Nov 19 2018, Andrew Lunn <andrew@...n.ch> wrote:
> 
> > On Mon, Nov 19, 2018 at 03:57:17PM +0100, Andreas Schwab wrote:
> >> On Okt 08 2018, Quentin Schulz <quentin.schulz@...tlin.com> wrote:
> >> 
> >> > The Microsemi PHYs have multiple banks of registers (called pages).
> >> > Registers can only be accessed from one page, if we need a register from
> >> > another page, we need to switch the page and the registers of all other
> >> > pages are not accessible anymore.
> >> >
> >> > Basically, to read register 5 from page 0, 1, 2, etc., you do the same
> >> > phy_read(phydev, 5); but you need to set the desired page beforehand.
> >> >
> >> > In order to guarantee that two concurrent functions do not change the
> >> > page, we need to do some locking per page. This can be achieved with the
> >> > use of phy_select_page and phy_restore_page functions but phy_write/read
> >> > calls in-between those two functions shall be replaced by their
> >> > lock-free alternative __phy_write/read.
> >> >
> >> > Let's migrate this driver to those functions.
> >> 
> >> This has some serious locking problem.
> >
> > Hi Andreas
> >
> > Could you be more specific. Are you getting a deadlock? A WARN_ON?
> 
> See the stack trace.  That's where it hangs.

So you never said it hangs. The stacktrace helps, but a description of
what actually happens also helps. And i expect Quentin has booted this
code lots of times and not had a hang. So some hits how to reproduce
it would also help. Maybe your kernel config?

I'm interested because he is using the core mdio locking
primitives. If those are broken, i want to know.

Thanks
	Andrew