linux-kernel - Re: [PATCH] kdb: use correct pointer when 'btc' calls 'btt'

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Message-ID: <20180916221822.GO11198@eros>
Date:   Mon, 17 Sep 2018 08:18:22 +1000
From:   "Tobin C. Harding" <me@...in.cc>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Christophe Leroy <christophe.leroy@....fr>,
        Jason Wessel <jason.wessel@...driver.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kgdb-bugreport@...ts.sourceforge.net, stable@...r.kernel.org
Subject: Re: [PATCH] kdb: use correct pointer when 'btc' calls 'btt'

On Sun, Sep 16, 2018 at 12:06:10PM -0700, Daniel Thompson wrote:
> On Fri, Sep 14, 2018 at 12:35:44PM +0000, Christophe Leroy wrote:
> > On a powerpc 8xx, 'btc' fails as follows:
> > 
> > Entering kdb (current=0x(ptrval), pid 282) due to Keyboard Entry
> > kdb> btc
> > btc: cpu status: Currently on cpu 0
> > Available cpus: 0
> > kdb_getarea: Bad address 0x0
> > 
> > when booting the kernel with 'debug_boot_weak_hash', it fails as well
> > 
> > Entering kdb (current=0xba99ad80, pid 284) due to Keyboard Entry
> > kdb> btc
> > btc: cpu status: Currently on cpu 0
> > Available cpus: 0
> > kdb_getarea: Bad address 0xba99ad80
> > 
> > On other platforms, Oopses have been observed too, see
> > https://github.com/linuxppc/linux/issues/139
> > 
> > This is due to btc calling 'btt' with %p pointer as an argument.
> > 
> > This patch replaces %p by %px to get the real pointer value as
> > expected by 'btt'
> > 
> > Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> > Cc: <stable@...r.kernel.org> # 4.15+
> 
> Would a Fixes: be better here?
> Fixes: ad67b74d2469d9b82 ("printk: hash addresses printed with %p")
> 
> No blame attached to Tobin, but the fixes makes it super clear what

:)

> changed and why this breaks kdb (which was not explicitly called out
> the patch description).
> 
> 
> Daniel.