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From: Doug Anderson <dianders@chromium.org>
To: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jason Wessel <jason.wessel@windriver.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andy Gross <agross@kernel.org>,
	kgdb-bugreport@lists.sourceforge.net,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-serial@vger.kernel.org, Sumit Garg <sumit.garg@linaro.org>,
	Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
	Will Deacon <will@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Frank Rowand <frowand.list@gmail.com>,
	bp@alien8.de, Bjorn Andersson <bjorn.andersson@linaro.org>,
	Jiri Slaby <jslaby@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	x86@kernel.org
Subject: Re: [PATCH v3 04/11] kgdb: Delay "kgdbwait" to dbg_late_init() by default
Date: Thu, 30 Apr 2020 09:35:30 -0700	[thread overview]
Message-ID: <CAD=FV=Ut7kHr+V_+Yyk=+NC5qBrKEQ+O6Ra4HRHs5XoAHFcWeA@mail.gmail.com> (raw)
In-Reply-To: <20200430154927.vhkhoffqwirb2fmm@holly.lan>

Hi,

On Thu, Apr 30, 2020 at 8:49 AM Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> On Tue, Apr 28, 2020 at 02:13:44PM -0700, Douglas Anderson wrote:
> > Using kgdb requires at least some level of architecture-level
> > initialization.  If nothing else, it relies on the architecture to
> > pass breakpoints / crashes onto kgdb.
> >
> > On some architectures this all works super early, specifically it
> > starts working at some point in time before Linux parses
> > early_params's.  On other architectures it doesn't.  A survey of a few
> > platforms:
> >
> > a) x86: Presumably it all works early since "ekgdboc" is documented to
> >    work here.
> > b) arm64: Catching crashes works; with a simple patch breakpoints can
> >    also be made to work.
> > c) arm: Nothing in kgdb works until
> >    paging_init() -> devicemaps_init() -> early_trap_init()
> >
> > Let's be conservative and, by default, process "kgdbwait" (which tells
> > the kernel to drop into the debugger ASAP at boot) a bit later at
> > dbg_late_init() time.  If an architecture has tested it and wants to
> > re-enable super early debugging, they can select the
> > ARCH_HAS_EARLY_DEBUG KConfig option.  We'll do this for x86 to start.
> > It should be noted that dbg_late_init() is still called quite early in
> > the system.
> >
> > Note that this patch doesn't affect when kgdb runs its init.  If kgdb
> > is set to initialize early it will still initialize when parsing
> > early_param's.  This patch _only_ inhibits the initial breakpoint from
> > "kgdbwait".  This means:
> >
> > * Without any extra patches arm64 platforms will at least catch
> >   crashes after kgdb inits.
> > * arm platforms will catch crashes (and could handle a hardcoded
> >   kgdb_breakpoint()) any time after early_trap_init() runs, even
> >   before dbg_late_init().
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Borislav Petkov <bp@alien8.de>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> It looks like this patch is triggering some warnings from the existing
> defconfigs (both x86 and arm64). It looks like this:
>
> ---
> wychelm$ make defconfig
>   GEN     Makefile
> *** Default configuration is based on 'x86_64_defconfig'
>
> WARNING: unmet direct dependencies detected for ARCH_HAS_EARLY_DEBUG
>   Depends on [n]: KGDB [=n]
>   Selected by [y]:
>   - X86 [=y]
>
> WARNING: unmet direct dependencies detected for ARCH_HAS_EARLY_DEBUG
>   Depends on [n]: KGDB [=n]
>   Selected by [y]:
>   - X86 [=y]

Ah, thanks!  I hadn't noticed those.  I think it'd be easy to just
change the relevant patches to just "select ARCH_HAS_EARLY_DEBUG if
KGDB".  If you agree that's a good fix and are willing, I'd be happy
if you just added it to the relevant patches when applying.  If not, I
can post a v4.

-Doug

  reply	other threads:[~2020-04-30 16:43 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-28 21:13 [PATCH v3 00/11] kgdb: Support late serial drivers; enable early debug w/ boot consoles Douglas Anderson
2020-04-28 21:13 ` [PATCH v3 01/11] kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb Douglas Anderson
2020-04-28 21:13 ` [PATCH v3 02/11] Revert "kgdboc: disable the console lock when in kgdb" Douglas Anderson
2020-04-28 21:13 ` [PATCH v3 03/11] kgdboc: Use a platform device to handle tty drivers showing up late Douglas Anderson
2020-04-28 21:13 ` [PATCH v3 04/11] kgdb: Delay "kgdbwait" to dbg_late_init() by default Douglas Anderson
2020-04-30 15:49   ` Daniel Thompson
2020-04-30 16:35     ` Doug Anderson [this message]
2020-05-04 14:43       ` [Kgdb-bugreport] " Daniel Thompson
2020-04-28 21:13 ` [PATCH v3 05/11] arm64: Add call_break_hook() to early_brk64() for early kgdb Douglas Anderson
2020-05-11 14:59   ` Will Deacon
2020-05-11 22:45     ` Doug Anderson
2020-05-12  7:35       ` Will Deacon
2020-05-12 15:27         ` Doug Anderson
2020-05-13  6:17           ` Will Deacon
2020-05-13 23:08             ` Doug Anderson
2020-04-28 21:13 ` [PATCH v3 06/11] kgdb: Prevent infinite recursive entries to the debugger Douglas Anderson
2020-04-30 16:52   ` Daniel Thompson
2020-04-28 21:13 ` [PATCH v3 07/11] kgdboc: Add kgdboc_earlycon to support early kgdb using boot consoles Douglas Anderson
2020-05-04 14:13   ` Daniel Thompson
2020-04-28 21:13 ` [PATCH v3 08/11] Documentation: kgdboc: Document new kgdboc_earlycon parameter Douglas Anderson
2020-05-04 14:40   ` Daniel Thompson
2020-04-28 21:13 ` [PATCH v3 09/11] serial: qcom_geni_serial: Support kgdboc_earlycon Douglas Anderson
2020-04-28 21:13 ` [PATCH v3 10/11] serial: 8250_early: " Douglas Anderson
2020-04-28 21:13 ` [PATCH v3 11/11] serial: amba-pl011: " Douglas Anderson

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