* [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles
@ 2020-04-21 21:14 Douglas Anderson
2020-04-21 21:14 ` [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter Douglas Anderson
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Douglas Anderson @ 2020-04-21 21:14 UTC (permalink / raw)
To: jason.wessel, daniel.thompson, gregkh
Cc: kgdb-bugreport, mingo, hpa, bp, linux-serial, agross, tglx,
frowand.list, bjorn.andersson, jslaby, catalin.marinas, corbet,
will, Douglas Anderson, Alexios Zavras, Allison Randal,
Andrew Morton, Arnd Bergmann, Borislav Petkov, Dave Martin,
Enrico Weigelt, Eric W. Biederman, James Morse, Juergen Gross,
Mark Rutland, Masami Hiramatsu, Matt Mullins,
Mauro Carvalho Chehab, Nadav Amit, Pawan Gupta, Peter Zijlstra,
Rick Edgecombe, jinho lim, linux-arm-kernel, linux-arm-msm,
linux-doc, linux-kernel, linux-usb, x86
This whole pile of patches was motivated by me trying to get kgdb to
work properly on a platform where my serial driver ended up being hit
by the -EPROBE_DEFER virus (it wasn't practicing social distancing
from other drivers). Specifically my serial driver's parent device
depended on a resource that wasn't available when its probe was first
called. It returned -EPROBE_DEFER which meant that when "kgdboc"
tried to run its setup the serial driver wasn't there. Unfortunately
"kgdboc" never tried again, so that meant that kgdb was disabled until
I manually enalbed it via sysfs.
While I could try to figure out how to get around the -EPROBE_DEFER
somehow, the above problems could happen to anyone and -EPROBE_DEFER
is generally considered something you just have to live with. In any
case the current "kgdboc" setup is a bit of a race waiting to happen.
I _think_ I saw during early testing that even adding a msleep() in
the typical serial driver's probe() is enough to trigger similar
issues.
I decided that for the above race the best attitude to get kgdb to
register at boot was probably "if you can't beat 'em, join 'em".
Thus, "kgdboc" now jumps on the -EPROBE_DEFER bandwagon (now that my
driver uses it it's no longer a virus). It does so a little awkwardly
because "kgdboc" hasn't normally had a "struct device" associated with
it, but it's really not _that_ ugly to make a platform device and
seems less ugly than alternatives.
Unfortunately now on my system the debugger is one of the last things
to register at boot. That's OK for debugging problems that show up
significantly after boot, but isn't so hot for all the boot problems
that I end up debugging. This motivated me to try to get something
working a little earlier.
My first attempt was to try to get the existing "ekgdboc" to work
earlier. I tried that for a bit until I realized that it needed to
work at the tty layer and I couldn't find any serial drivers that
managed to register themselves to the tty layer super early at boot.
The only documented use of "ekgdboc" is "ekgdboc=kbd" and that's a bit
of a special snowflake. Trying to get my serial driver and all its
dependencies to probe normally and register the tty driver super early
at boot seemed like a bad way to go. In fact, all the complexity
needed to do something like this is why the system already has a
special concept of a "boot console" that lives only long enough to
transition to the normal console.
Leveraging the boot console seemed like a good way to go and that's
what this series does. I found that consoles could have a read()
function, though I couldn't find anyone who implemented it. I
implemented it for two serial drivers for the devices I had easy
access to, making the assumption that for boot consoles that we could
assume read() and write() were polling-compatible (seems sane I
think).
Now anyone who makes a small change to their serial driver can easily
enable early kgdb debugging!
The devices I had for testing were:
- arm32: rk3288-veyron-jerry
- arm64: rk3399-gru-kevin
- arm64: qcom-sc7180-trogdor (not mainline yet)
These are the devices I tested this series on. I tried to test
various combinations of enabling/disabling various options and I
hopefully caught the corner cases, but I'd appreciate any extra
testing people can do. Notably I didn't test on x86, but (I think) I
didn't touch much there so I shouldn't have broken anything.
When testing I found a few problems with actually dropping into the
debugger super early on arm and arm64 devices. Patches in this series
should help with this. For arm I just avoid dropping into the
debugger until a little later and for arm64 I actually enable
debugging super early.
I realize that bits of this series might feel a little hacky, though
I've tried to do things in the cleanest way I could without overly
interferring with the rest of the kernel. If you hate the way I
solved a problem I would love it if you could provide guidance on how
you think I could solve the problem better.
This series (and my comments / documentation / commit messages) are
now long enough that my eyes glaze over when I try to read it all over
to double-check. I've nontheless tried to double-check it, but I'm
pretty sure I did something stupid. Thank you ahead of time for
pointing it out to me so I can fix it in v3. If somehow I managed to
not do anything stupid (really?) then thank you for double-checking me
anyway.
Changes in v2:
- ("kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb") new for v2.
- ("Revert "kgdboc: disable the console lock when in kgdb"") new for v2.
- Assumes we have ("kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb")
- Fix kgdbts, tty/mips_ejtag_fdc, and usb/early/ehci-dbgp
Douglas Anderson (9):
kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb
Revert "kgdboc: disable the console lock when in kgdb"
kgdboc: Use a platform device to handle tty drivers showing up late
kgdb: Delay "kgdbwait" to dbg_late_init() by default
arm64: Add call_break_hook() to early_brk64() for early kgdb
kgdboc: Add earlycon_kgdboc to support early kgdb using boot consoles
Documentation: kgdboc: Document new earlycon_kgdboc parameter
serial: qcom_geni_serial: Support earlycon_kgdboc
serial: 8250_early: Support earlycon_kgdboc
.../admin-guide/kernel-parameters.txt | 20 ++
Documentation/dev-tools/kgdb.rst | 14 +
arch/arm64/include/asm/debug-monitors.h | 2 +
arch/arm64/kernel/debug-monitors.c | 2 +-
arch/arm64/kernel/kgdb.c | 5 +
arch/arm64/kernel/traps.c | 3 +
arch/x86/kernel/kgdb.c | 5 +
drivers/misc/kgdbts.c | 2 +-
drivers/tty/mips_ejtag_fdc.c | 2 +-
drivers/tty/serial/8250/8250_early.c | 23 ++
drivers/tty/serial/kgdboc.c | 262 ++++++++++++++++--
drivers/tty/serial/qcom_geni_serial.c | 32 +++
drivers/usb/early/ehci-dbgp.c | 2 +-
include/linux/kgdb.h | 25 +-
kernel/debug/debug_core.c | 48 +++-
15 files changed, 400 insertions(+), 47 deletions(-)
--
2.26.1.301.g55bc3eb7cb9-goog
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter
2020-04-21 21:14 [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Douglas Anderson
@ 2020-04-21 21:14 ` Douglas Anderson
2020-04-27 16:46 ` Daniel Thompson
2020-04-23 13:50 ` [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Greg KH
2020-04-24 8:32 ` Sumit Garg
2 siblings, 1 reply; 7+ messages in thread
From: Douglas Anderson @ 2020-04-21 21:14 UTC (permalink / raw)
To: jason.wessel, daniel.thompson, gregkh
Cc: kgdb-bugreport, mingo, hpa, bp, linux-serial, agross, tglx,
frowand.list, bjorn.andersson, jslaby, catalin.marinas, corbet,
will, Douglas Anderson, Andrew Morton, Borislav Petkov,
Juergen Gross, Mauro Carvalho Chehab, Pawan Gupta, linux-doc,
linux-kernel
The recent patch ("kgdboc: Add earlycon_kgdboc to support early kgdb
using boot consoles") adds a new kernel command line parameter.
Document it.
Note that the patch adding the feature does some comparing/contrasting
of "earlycon_kgdboc" vs. the existing "ekgdboc". See that patch for
more details, but briefly "ekgdboc" can be used _instead_ of "kgdboc"
and just makes "kgdboc" do its normal initialization early (only works
if your tty driver is already ready). The new "earlycon_kgdboc" works
in combination with "kgdboc" and is backed by boot consoles.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
Changes in v2: None
.../admin-guide/kernel-parameters.txt | 20 +++++++++++++++++++
Documentation/dev-tools/kgdb.rst | 14 +++++++++++++
2 files changed, 34 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f2a93c8679e8..588625ec2993 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1132,6 +1132,22 @@
address must be provided, and the serial port must
already be setup and configured.
+ earlycon_kgdboc= [KGDB,HW]
+ If the boot console provides the ability to read
+ characters and can work in polling mode, you can use
+ this parameter to tell kgdb to use it as a backend
+ until the normal console is registered. Intended to
+ be used together with the kgdboc parameter which
+ specifies the normal console to transition to.
+
+ The the name of the early console should be specified
+ as the value of this parameter. Note that the name of
+ the early console might be different than the tty
+ name passed to kgdboc. If only one boot console with
+ a read() function is enabled it's OK to leave the
+ value blank and the first boot console that implements
+ read() will be picked.
+
earlyprintk= [X86,SH,ARM,M68k,S390]
earlyprintk=vga
earlyprintk=sclp
@@ -1190,6 +1206,10 @@
This is designed to be used in conjunction with
the boot argument: earlyprintk=vga
+ This parameter works in place of the kgdboc parameter
+ but can only be used if the backing tty is available
+ very early in the boot process.
+
edd= [EDD]
Format: {"off" | "on" | "skip[mbr]"}
diff --git a/Documentation/dev-tools/kgdb.rst b/Documentation/dev-tools/kgdb.rst
index d38be58f872a..c0b321403d9a 100644
--- a/Documentation/dev-tools/kgdb.rst
+++ b/Documentation/dev-tools/kgdb.rst
@@ -274,6 +274,20 @@ don't like this are to hack gdb to send the :kbd:`SysRq-G` for you as well as
on the initial connect, or to use a debugger proxy that allows an
unmodified gdb to do the debugging.
+Kernel parameter: ``earlycon_kgdboc``
+-------------------------------------
+
+If you specify the kernel parameter ``earlycon_kgdboc`` and your serial
+driver registers a boot console that supports polling (doesn't need
+interrupts and implements a nonblocking read() function) kgdb will attempt
+to work using the boot console until it can transition to the regular
+tty driver specified by the ``kgdboc`` parameter.
+
+Normally there is only one boot console (especially that implements the
+read() function) so just adding ``earlycon_kgdboc`` on its own is
+sufficient to make this work. If you have more than one boot console you
+can add the boot console's name to differentiate.
+
Kernel parameter: ``kgdbwait``
------------------------------
--
2.26.1.301.g55bc3eb7cb9-goog
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles
2020-04-21 21:14 [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Douglas Anderson
2020-04-21 21:14 ` [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter Douglas Anderson
@ 2020-04-23 13:50 ` Greg KH
2020-04-24 8:32 ` Sumit Garg
2 siblings, 0 replies; 7+ messages in thread
From: Greg KH @ 2020-04-23 13:50 UTC (permalink / raw)
To: Douglas Anderson
Cc: jason.wessel, daniel.thompson, kgdb-bugreport, mingo, hpa, bp,
linux-serial, agross, tglx, frowand.list, bjorn.andersson,
jslaby, catalin.marinas, corbet, will, Alexios Zavras,
Allison Randal, Andrew Morton, Arnd Bergmann, Borislav Petkov,
Dave Martin, Enrico Weigelt, Eric W. Biederman, James Morse,
Juergen Gross, Mark Rutland, Masami Hiramatsu, Matt Mullins,
Mauro Carvalho Chehab, Nadav Amit, Pawan Gupta, Peter Zijlstra,
Rick Edgecombe, jinho lim, linux-arm-kernel, linux-arm-msm,
linux-doc, linux-kernel, linux-usb, x86
On Tue, Apr 21, 2020 at 02:14:38PM -0700, Douglas Anderson wrote:
> This whole pile of patches was motivated by me trying to get kgdb to
> work properly on a platform where my serial driver ended up being hit
> by the -EPROBE_DEFER virus (it wasn't practicing social distancing
> from other drivers). Specifically my serial driver's parent device
> depended on a resource that wasn't available when its probe was first
> called. It returned -EPROBE_DEFER which meant that when "kgdboc"
> tried to run its setup the serial driver wasn't there. Unfortunately
> "kgdboc" never tried again, so that meant that kgdb was disabled until
> I manually enalbed it via sysfs.
>
> While I could try to figure out how to get around the -EPROBE_DEFER
> somehow, the above problems could happen to anyone and -EPROBE_DEFER
> is generally considered something you just have to live with. In any
> case the current "kgdboc" setup is a bit of a race waiting to happen.
> I _think_ I saw during early testing that even adding a msleep() in
> the typical serial driver's probe() is enough to trigger similar
> issues.
>
> I decided that for the above race the best attitude to get kgdb to
> register at boot was probably "if you can't beat 'em, join 'em".
> Thus, "kgdboc" now jumps on the -EPROBE_DEFER bandwagon (now that my
> driver uses it it's no longer a virus). It does so a little awkwardly
> because "kgdboc" hasn't normally had a "struct device" associated with
> it, but it's really not _that_ ugly to make a platform device and
> seems less ugly than alternatives.
>
> Unfortunately now on my system the debugger is one of the last things
> to register at boot. That's OK for debugging problems that show up
> significantly after boot, but isn't so hot for all the boot problems
> that I end up debugging. This motivated me to try to get something
> working a little earlier.
>
> My first attempt was to try to get the existing "ekgdboc" to work
> earlier. I tried that for a bit until I realized that it needed to
> work at the tty layer and I couldn't find any serial drivers that
> managed to register themselves to the tty layer super early at boot.
> The only documented use of "ekgdboc" is "ekgdboc=kbd" and that's a bit
> of a special snowflake. Trying to get my serial driver and all its
> dependencies to probe normally and register the tty driver super early
> at boot seemed like a bad way to go. In fact, all the complexity
> needed to do something like this is why the system already has a
> special concept of a "boot console" that lives only long enough to
> transition to the normal console.
>
> Leveraging the boot console seemed like a good way to go and that's
> what this series does. I found that consoles could have a read()
> function, though I couldn't find anyone who implemented it. I
> implemented it for two serial drivers for the devices I had easy
> access to, making the assumption that for boot consoles that we could
> assume read() and write() were polling-compatible (seems sane I
> think).
>
> Now anyone who makes a small change to their serial driver can easily
> enable early kgdb debugging!
>
> The devices I had for testing were:
> - arm32: rk3288-veyron-jerry
> - arm64: rk3399-gru-kevin
> - arm64: qcom-sc7180-trogdor (not mainline yet)
>
> These are the devices I tested this series on. I tried to test
> various combinations of enabling/disabling various options and I
> hopefully caught the corner cases, but I'd appreciate any extra
> testing people can do. Notably I didn't test on x86, but (I think) I
> didn't touch much there so I shouldn't have broken anything.
>
> When testing I found a few problems with actually dropping into the
> debugger super early on arm and arm64 devices. Patches in this series
> should help with this. For arm I just avoid dropping into the
> debugger until a little later and for arm64 I actually enable
> debugging super early.
>
> I realize that bits of this series might feel a little hacky, though
> I've tried to do things in the cleanest way I could without overly
> interferring with the rest of the kernel. If you hate the way I
> solved a problem I would love it if you could provide guidance on how
> you think I could solve the problem better.
>
> This series (and my comments / documentation / commit messages) are
> now long enough that my eyes glaze over when I try to read it all over
> to double-check. I've nontheless tried to double-check it, but I'm
> pretty sure I did something stupid. Thank you ahead of time for
> pointing it out to me so I can fix it in v3. If somehow I managed to
> not do anything stupid (really?) then thank you for double-checking me
> anyway.
>
> Changes in v2:
> - ("kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb") new for v2.
> - ("Revert "kgdboc: disable the console lock when in kgdb"") new for v2.
> - Assumes we have ("kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb")
> - Fix kgdbts, tty/mips_ejtag_fdc, and usb/early/ehci-dbgp
>
> Douglas Anderson (9):
> kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb
> Revert "kgdboc: disable the console lock when in kgdb"
> kgdboc: Use a platform device to handle tty drivers showing up late
> kgdb: Delay "kgdbwait" to dbg_late_init() by default
> arm64: Add call_break_hook() to early_brk64() for early kgdb
> kgdboc: Add earlycon_kgdboc to support early kgdb using boot consoles
> Documentation: kgdboc: Document new earlycon_kgdboc parameter
> serial: qcom_geni_serial: Support earlycon_kgdboc
> serial: 8250_early: Support earlycon_kgdboc
>
> .../admin-guide/kernel-parameters.txt | 20 ++
> Documentation/dev-tools/kgdb.rst | 14 +
> arch/arm64/include/asm/debug-monitors.h | 2 +
> arch/arm64/kernel/debug-monitors.c | 2 +-
> arch/arm64/kernel/kgdb.c | 5 +
> arch/arm64/kernel/traps.c | 3 +
> arch/x86/kernel/kgdb.c | 5 +
> drivers/misc/kgdbts.c | 2 +-
> drivers/tty/mips_ejtag_fdc.c | 2 +-
> drivers/tty/serial/8250/8250_early.c | 23 ++
> drivers/tty/serial/kgdboc.c | 262 ++++++++++++++++--
> drivers/tty/serial/qcom_geni_serial.c | 32 +++
> drivers/usb/early/ehci-dbgp.c | 2 +-
> include/linux/kgdb.h | 25 +-
> kernel/debug/debug_core.c | 48 +++-
> 15 files changed, 400 insertions(+), 47 deletions(-)
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles
2020-04-21 21:14 [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Douglas Anderson
2020-04-21 21:14 ` [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter Douglas Anderson
2020-04-23 13:50 ` [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Greg KH
@ 2020-04-24 8:32 ` Sumit Garg
2020-04-24 10:13 ` Daniel Thompson
2 siblings, 1 reply; 7+ messages in thread
From: Sumit Garg @ 2020-04-24 8:32 UTC (permalink / raw)
To: Douglas Anderson
Cc: jason.wessel, Daniel Thompson, Greg Kroah-Hartman, Mark Rutland,
Linux Doc Mailing List, Peter Zijlstra, catalin.marinas,
bjorn.andersson, Nadav Amit, hpa, Mauro Carvalho Chehab, will,
Matt Mullins, Jonathan Corbet, frowand.list, x86, jinho lim,
agross, Pawan Gupta, linux-arm-kernel, linux-serial,
kgdb-bugreport, Borislav Petkov, Dave Martin, Masami Hiramatsu,
Arnd Bergmann, linux-arm-msm, jslaby, Alexios Zavras, bp, tglx,
mingo, Allison Randal, Juergen Gross, linux-usb,
Linux Kernel Mailing List, James Morse, Eric W. Biederman,
Andrew Morton, Rick Edgecombe, Enrico Weigelt
Hi Doug,
On Wed, 22 Apr 2020 at 02:45, Douglas Anderson <dianders@chromium.org> wrote:
>
> This whole pile of patches was motivated by me trying to get kgdb to
> work properly on a platform where my serial driver ended up being hit
> by the -EPROBE_DEFER virus (it wasn't practicing social distancing
> from other drivers). Specifically my serial driver's parent device
> depended on a resource that wasn't available when its probe was first
> called. It returned -EPROBE_DEFER which meant that when "kgdboc"
> tried to run its setup the serial driver wasn't there. Unfortunately
> "kgdboc" never tried again, so that meant that kgdb was disabled until
> I manually enalbed it via sysfs.
>
> While I could try to figure out how to get around the -EPROBE_DEFER
> somehow, the above problems could happen to anyone and -EPROBE_DEFER
> is generally considered something you just have to live with. In any
> case the current "kgdboc" setup is a bit of a race waiting to happen.
> I _think_ I saw during early testing that even adding a msleep() in
> the typical serial driver's probe() is enough to trigger similar
> issues.
>
> I decided that for the above race the best attitude to get kgdb to
> register at boot was probably "if you can't beat 'em, join 'em".
> Thus, "kgdboc" now jumps on the -EPROBE_DEFER bandwagon (now that my
> driver uses it it's no longer a virus). It does so a little awkwardly
> because "kgdboc" hasn't normally had a "struct device" associated with
> it, but it's really not _that_ ugly to make a platform device and
> seems less ugly than alternatives.
>
> Unfortunately now on my system the debugger is one of the last things
> to register at boot. That's OK for debugging problems that show up
> significantly after boot, but isn't so hot for all the boot problems
> that I end up debugging. This motivated me to try to get something
> working a little earlier.
>
> My first attempt was to try to get the existing "ekgdboc" to work
> earlier. I tried that for a bit until I realized that it needed to
> work at the tty layer and I couldn't find any serial drivers that
> managed to register themselves to the tty layer super early at boot.
> The only documented use of "ekgdboc" is "ekgdboc=kbd" and that's a bit
> of a special snowflake. Trying to get my serial driver and all its
> dependencies to probe normally and register the tty driver super early
> at boot seemed like a bad way to go. In fact, all the complexity
> needed to do something like this is why the system already has a
> special concept of a "boot console" that lives only long enough to
> transition to the normal console.
>
> Leveraging the boot console seemed like a good way to go and that's
> what this series does. I found that consoles could have a read()
> function, though I couldn't find anyone who implemented it. I
> implemented it for two serial drivers for the devices I had easy
> access to, making the assumption that for boot consoles that we could
> assume read() and write() were polling-compatible (seems sane I
> think).
>
> Now anyone who makes a small change to their serial driver can easily
> enable early kgdb debugging!
>
> The devices I had for testing were:
> - arm32: rk3288-veyron-jerry
> - arm64: rk3399-gru-kevin
> - arm64: qcom-sc7180-trogdor (not mainline yet)
>
> These are the devices I tested this series on. I tried to test
> various combinations of enabling/disabling various options and I
> hopefully caught the corner cases, but I'd appreciate any extra
> testing people can do.
earlycon_kgdboc sounds like a really cool feature. So I gave it a try
on my arm64 machine (Developerbox) and it works like a charm. So for
patch 6/9 you can add:
Tested-by: Sumit Garg <sumit.garg@linaro.org>
Plus, in order to enable earlycon_kgdboc on Developerbox I had to
implement the read() function in the early console driver for
amba-pl011 (see patch [1]). It would be great if you could pick that
patch [1] too as part of this series.
[1] https://lkml.org/lkml/2020/4/24/173
-Sumit
> Notably I didn't test on x86, but (I think) I
> didn't touch much there so I shouldn't have broken anything.
>
> When testing I found a few problems with actually dropping into the
> debugger super early on arm and arm64 devices. Patches in this series
> should help with this. For arm I just avoid dropping into the
> debugger until a little later and for arm64 I actually enable
> debugging super early.
>
> I realize that bits of this series might feel a little hacky, though
> I've tried to do things in the cleanest way I could without overly
> interferring with the rest of the kernel. If you hate the way I
> solved a problem I would love it if you could provide guidance on how
> you think I could solve the problem better.
>
> This series (and my comments / documentation / commit messages) are
> now long enough that my eyes glaze over when I try to read it all over
> to double-check. I've nontheless tried to double-check it, but I'm
> pretty sure I did something stupid. Thank you ahead of time for
> pointing it out to me so I can fix it in v3. If somehow I managed to
> not do anything stupid (really?) then thank you for double-checking me
> anyway.
>
> Changes in v2:
> - ("kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb") new for v2.
> - ("Revert "kgdboc: disable the console lock when in kgdb"") new for v2.
> - Assumes we have ("kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb")
> - Fix kgdbts, tty/mips_ejtag_fdc, and usb/early/ehci-dbgp
>
> Douglas Anderson (9):
> kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb
> Revert "kgdboc: disable the console lock when in kgdb"
> kgdboc: Use a platform device to handle tty drivers showing up late
> kgdb: Delay "kgdbwait" to dbg_late_init() by default
> arm64: Add call_break_hook() to early_brk64() for early kgdb
> kgdboc: Add earlycon_kgdboc to support early kgdb using boot consoles
> Documentation: kgdboc: Document new earlycon_kgdboc parameter
> serial: qcom_geni_serial: Support earlycon_kgdboc
> serial: 8250_early: Support earlycon_kgdboc
>
> .../admin-guide/kernel-parameters.txt | 20 ++
> Documentation/dev-tools/kgdb.rst | 14 +
> arch/arm64/include/asm/debug-monitors.h | 2 +
> arch/arm64/kernel/debug-monitors.c | 2 +-
> arch/arm64/kernel/kgdb.c | 5 +
> arch/arm64/kernel/traps.c | 3 +
> arch/x86/kernel/kgdb.c | 5 +
> drivers/misc/kgdbts.c | 2 +-
> drivers/tty/mips_ejtag_fdc.c | 2 +-
> drivers/tty/serial/8250/8250_early.c | 23 ++
> drivers/tty/serial/kgdboc.c | 262 ++++++++++++++++--
> drivers/tty/serial/qcom_geni_serial.c | 32 +++
> drivers/usb/early/ehci-dbgp.c | 2 +-
> include/linux/kgdb.h | 25 +-
> kernel/debug/debug_core.c | 48 +++-
> 15 files changed, 400 insertions(+), 47 deletions(-)
>
> --
> 2.26.1.301.g55bc3eb7cb9-goog
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles
2020-04-24 8:32 ` Sumit Garg
@ 2020-04-24 10:13 ` Daniel Thompson
0 siblings, 0 replies; 7+ messages in thread
From: Daniel Thompson @ 2020-04-24 10:13 UTC (permalink / raw)
To: Sumit Garg
Cc: Douglas Anderson, jason.wessel, Greg Kroah-Hartman, Mark Rutland,
Linux Doc Mailing List, Peter Zijlstra, catalin.marinas,
bjorn.andersson, Nadav Amit, hpa, Mauro Carvalho Chehab, will,
Matt Mullins, Jonathan Corbet, frowand.list, x86, jinho lim,
agross, Pawan Gupta, linux-arm-kernel, linux-serial,
kgdb-bugreport, Borislav Petkov, Dave Martin, Masami Hiramatsu,
Arnd Bergmann, linux-arm-msm, jslaby, Alexios Zavras, bp, tglx,
mingo, Allison Randal, Juergen Gross, linux-usb,
Linux Kernel Mailing List, James Morse, Eric W. Biederman,
Andrew Morton, Rick Edgecombe, Enrico Weigelt
On Fri, Apr 24, 2020 at 02:02:51PM +0530, Sumit Garg wrote:
> Hi Doug,
>
> On Wed, 22 Apr 2020 at 02:45, Douglas Anderson <dianders@chromium.org> wrote:
> >
> > This whole pile of patches was motivated by me trying to get kgdb to
> > work properly on a platform where my serial driver ended up being hit
> > by the -EPROBE_DEFER virus (it wasn't practicing social distancing
> > from other drivers). Specifically my serial driver's parent device
> > depended on a resource that wasn't available when its probe was first
> > called. It returned -EPROBE_DEFER which meant that when "kgdboc"
> > tried to run its setup the serial driver wasn't there. Unfortunately
> > "kgdboc" never tried again, so that meant that kgdb was disabled until
> > I manually enalbed it via sysfs.
> >
> > While I could try to figure out how to get around the -EPROBE_DEFER
> > somehow, the above problems could happen to anyone and -EPROBE_DEFER
> > is generally considered something you just have to live with. In any
> > case the current "kgdboc" setup is a bit of a race waiting to happen.
> > I _think_ I saw during early testing that even adding a msleep() in
> > the typical serial driver's probe() is enough to trigger similar
> > issues.
> >
> > I decided that for the above race the best attitude to get kgdb to
> > register at boot was probably "if you can't beat 'em, join 'em".
> > Thus, "kgdboc" now jumps on the -EPROBE_DEFER bandwagon (now that my
> > driver uses it it's no longer a virus). It does so a little awkwardly
> > because "kgdboc" hasn't normally had a "struct device" associated with
> > it, but it's really not _that_ ugly to make a platform device and
> > seems less ugly than alternatives.
> >
> > Unfortunately now on my system the debugger is one of the last things
> > to register at boot. That's OK for debugging problems that show up
> > significantly after boot, but isn't so hot for all the boot problems
> > that I end up debugging. This motivated me to try to get something
> > working a little earlier.
> >
> > My first attempt was to try to get the existing "ekgdboc" to work
> > earlier. I tried that for a bit until I realized that it needed to
> > work at the tty layer and I couldn't find any serial drivers that
> > managed to register themselves to the tty layer super early at boot.
> > The only documented use of "ekgdboc" is "ekgdboc=kbd" and that's a bit
> > of a special snowflake. Trying to get my serial driver and all its
> > dependencies to probe normally and register the tty driver super early
> > at boot seemed like a bad way to go. In fact, all the complexity
> > needed to do something like this is why the system already has a
> > special concept of a "boot console" that lives only long enough to
> > transition to the normal console.
> >
> > Leveraging the boot console seemed like a good way to go and that's
> > what this series does. I found that consoles could have a read()
> > function, though I couldn't find anyone who implemented it. I
> > implemented it for two serial drivers for the devices I had easy
> > access to, making the assumption that for boot consoles that we could
> > assume read() and write() were polling-compatible (seems sane I
> > think).
> >
> > Now anyone who makes a small change to their serial driver can easily
> > enable early kgdb debugging!
> >
> > The devices I had for testing were:
> > - arm32: rk3288-veyron-jerry
> > - arm64: rk3399-gru-kevin
> > - arm64: qcom-sc7180-trogdor (not mainline yet)
> >
> > These are the devices I tested this series on. I tried to test
> > various combinations of enabling/disabling various options and I
> > hopefully caught the corner cases, but I'd appreciate any extra
> > testing people can do.
>
> earlycon_kgdboc sounds like a really cool feature. So I gave it a try
> on my arm64 machine (Developerbox) and it works like a charm. So for
> patch 6/9 you can add:
>
> Tested-by: Sumit Garg <sumit.garg@linaro.org>
>
> Plus, in order to enable earlycon_kgdboc on Developerbox I had to
> implement the read() function in the early console driver for
> amba-pl011 (see patch [1]). It would be great if you could pick that
> patch [1] too as part of this series.
>
> [1] https://lkml.org/lkml/2020/4/24/173
I think PL011 support is also useful for getting this feature integrated
into the test suite too!
Daniel.
>
> -Sumit
>
> > Notably I didn't test on x86, but (I think) I
> > didn't touch much there so I shouldn't have broken anything.
> >
> > When testing I found a few problems with actually dropping into the
> > debugger super early on arm and arm64 devices. Patches in this series
> > should help with this. For arm I just avoid dropping into the
> > debugger until a little later and for arm64 I actually enable
> > debugging super early.
> >
> > I realize that bits of this series might feel a little hacky, though
> > I've tried to do things in the cleanest way I could without overly
> > interferring with the rest of the kernel. If you hate the way I
> > solved a problem I would love it if you could provide guidance on how
> > you think I could solve the problem better.
> >
> > This series (and my comments / documentation / commit messages) are
> > now long enough that my eyes glaze over when I try to read it all over
> > to double-check. I've nontheless tried to double-check it, but I'm
> > pretty sure I did something stupid. Thank you ahead of time for
> > pointing it out to me so I can fix it in v3. If somehow I managed to
> > not do anything stupid (really?) then thank you for double-checking me
> > anyway.
> >
> > Changes in v2:
> > - ("kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb") new for v2.
> > - ("Revert "kgdboc: disable the console lock when in kgdb"") new for v2.
> > - Assumes we have ("kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb")
> > - Fix kgdbts, tty/mips_ejtag_fdc, and usb/early/ehci-dbgp
> >
> > Douglas Anderson (9):
> > kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb
> > Revert "kgdboc: disable the console lock when in kgdb"
> > kgdboc: Use a platform device to handle tty drivers showing up late
> > kgdb: Delay "kgdbwait" to dbg_late_init() by default
> > arm64: Add call_break_hook() to early_brk64() for early kgdb
> > kgdboc: Add earlycon_kgdboc to support early kgdb using boot consoles
> > Documentation: kgdboc: Document new earlycon_kgdboc parameter
> > serial: qcom_geni_serial: Support earlycon_kgdboc
> > serial: 8250_early: Support earlycon_kgdboc
> >
> > .../admin-guide/kernel-parameters.txt | 20 ++
> > Documentation/dev-tools/kgdb.rst | 14 +
> > arch/arm64/include/asm/debug-monitors.h | 2 +
> > arch/arm64/kernel/debug-monitors.c | 2 +-
> > arch/arm64/kernel/kgdb.c | 5 +
> > arch/arm64/kernel/traps.c | 3 +
> > arch/x86/kernel/kgdb.c | 5 +
> > drivers/misc/kgdbts.c | 2 +-
> > drivers/tty/mips_ejtag_fdc.c | 2 +-
> > drivers/tty/serial/8250/8250_early.c | 23 ++
> > drivers/tty/serial/kgdboc.c | 262 ++++++++++++++++--
> > drivers/tty/serial/qcom_geni_serial.c | 32 +++
> > drivers/usb/early/ehci-dbgp.c | 2 +-
> > include/linux/kgdb.h | 25 +-
> > kernel/debug/debug_core.c | 48 +++-
> > 15 files changed, 400 insertions(+), 47 deletions(-)
> >
> > --
> > 2.26.1.301.g55bc3eb7cb9-goog
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter
2020-04-21 21:14 ` [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter Douglas Anderson
@ 2020-04-27 16:46 ` Daniel Thompson
2020-04-28 21:32 ` Doug Anderson
0 siblings, 1 reply; 7+ messages in thread
From: Daniel Thompson @ 2020-04-27 16:46 UTC (permalink / raw)
To: Douglas Anderson
Cc: jason.wessel, gregkh, kgdb-bugreport, mingo, hpa, bp,
linux-serial, agross, tglx, frowand.list, bjorn.andersson,
jslaby, catalin.marinas, corbet, will, Andrew Morton,
Borislav Petkov, Juergen Gross, Mauro Carvalho Chehab,
Pawan Gupta, linux-doc, linux-kernel
On Tue, Apr 21, 2020 at 02:14:45PM -0700, Douglas Anderson wrote:
> The recent patch ("kgdboc: Add earlycon_kgdboc to support early kgdb
> using boot consoles") adds a new kernel command line parameter.
> Document it.
>
> Note that the patch adding the feature does some comparing/contrasting
> of "earlycon_kgdboc" vs. the existing "ekgdboc". See that patch for
> more details, but briefly "ekgdboc" can be used _instead_ of "kgdboc"
> and just makes "kgdboc" do its normal initialization early (only works
> if your tty driver is already ready). The new "earlycon_kgdboc" works
> in combination with "kgdboc" and is backed by boot consoles.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
>
> Changes in v2: None
>
> .../admin-guide/kernel-parameters.txt | 20 +++++++++++++++++++
> Documentation/dev-tools/kgdb.rst | 14 +++++++++++++
> 2 files changed, 34 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f2a93c8679e8..588625ec2993 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1132,6 +1132,22 @@
> address must be provided, and the serial port must
> already be setup and configured.
>
> + earlycon_kgdboc= [KGDB,HW]
> + If the boot console provides the ability to read
> + characters and can work in polling mode, you can use
> + this parameter to tell kgdb to use it as a backend
> + until the normal console is registered. Intended to
> + be used together with the kgdboc parameter which
> + specifies the normal console to transition to.
> +
> + The the name of the early console should be specified
> + as the value of this parameter. Note that the name of
> + the early console might be different than the tty
> + name passed to kgdboc. If only one boot console with
> + a read() function is enabled it's OK to leave the
> + value blank and the first boot console that implements
> + read() will be picked.
There's no need for the "If only one boot console with a read()
funcuiton is enabled" here,
Seeing this in alphabetic order in this patch it also crosses my mind
that kgdboc_earlycon might be a better name so that is sorts closer
to the other kgdb options. This is a kgdboc feature that uses earlycon
not an earlycon feature that uses kgdboc.
> +
> earlyprintk= [X86,SH,ARM,M68k,S390]
> earlyprintk=vga
> earlyprintk=sclp
> @@ -1190,6 +1206,10 @@
> This is designed to be used in conjunction with
> the boot argument: earlyprintk=vga
>
> + This parameter works in place of the kgdboc parameter
> + but can only be used if the backing tty is available
> + very early in the boot process.
> +
I wonder if pragmatic advice is more useful:
For early debugging via a serial port see earlycon_kgdboc instead.
> edd= [EDD]
> Format: {"off" | "on" | "skip[mbr]"}
>
> diff --git a/Documentation/dev-tools/kgdb.rst b/Documentation/dev-tools/kgdb.rst
> index d38be58f872a..c0b321403d9a 100644
> --- a/Documentation/dev-tools/kgdb.rst
> +++ b/Documentation/dev-tools/kgdb.rst
> @@ -274,6 +274,20 @@ don't like this are to hack gdb to send the :kbd:`SysRq-G` for you as well as
> on the initial connect, or to use a debugger proxy that allows an
> unmodified gdb to do the debugging.
>
> +Kernel parameter: ``earlycon_kgdboc``
> +-------------------------------------
> +
> +If you specify the kernel parameter ``earlycon_kgdboc`` and your serial
> +driver registers a boot console that supports polling (doesn't need
> +interrupts and implements a nonblocking read() function) kgdb will attempt
> +to work using the boot console until it can transition to the regular
> +tty driver specified by the ``kgdboc`` parameter.
> +
> +Normally there is only one boot console (especially that implements the
> +read() function) so just adding ``earlycon_kgdboc`` on its own is
> +sufficient to make this work. If you have more than one boot console you
> +can add the boot console's name to differentiate.
> +
I think we need an example here. The example in the patch header for
the previous patch was useful (at least for me).
Daniel.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter
2020-04-27 16:46 ` Daniel Thompson
@ 2020-04-28 21:32 ` Doug Anderson
0 siblings, 0 replies; 7+ messages in thread
From: Doug Anderson @ 2020-04-28 21:32 UTC (permalink / raw)
To: Daniel Thompson
Cc: Jason Wessel, Greg Kroah-Hartman, kgdb-bugreport, Ingo Molnar,
H. Peter Anvin, bp, linux-serial, Andy Gross, Thomas Gleixner,
Frank Rowand, Bjorn Andersson, Jiri Slaby, Catalin Marinas,
Jonathan Corbet, Will Deacon, Andrew Morton, Borislav Petkov,
Juergen Gross, Mauro Carvalho Chehab, Pawan Gupta, linux-doc,
LKML
Hi,
On Mon, Apr 27, 2020 at 9:46 AM Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> On Tue, Apr 21, 2020 at 02:14:45PM -0700, Douglas Anderson wrote:
> > The recent patch ("kgdboc: Add earlycon_kgdboc to support early kgdb
> > using boot consoles") adds a new kernel command line parameter.
> > Document it.
> >
> > Note that the patch adding the feature does some comparing/contrasting
> > of "earlycon_kgdboc" vs. the existing "ekgdboc". See that patch for
> > more details, but briefly "ekgdboc" can be used _instead_ of "kgdboc"
> > and just makes "kgdboc" do its normal initialization early (only works
> > if your tty driver is already ready). The new "earlycon_kgdboc" works
> > in combination with "kgdboc" and is backed by boot consoles.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> > Changes in v2: None
> >
> > .../admin-guide/kernel-parameters.txt | 20 +++++++++++++++++++
> > Documentation/dev-tools/kgdb.rst | 14 +++++++++++++
> > 2 files changed, 34 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index f2a93c8679e8..588625ec2993 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -1132,6 +1132,22 @@
> > address must be provided, and the serial port must
> > already be setup and configured.
> >
> > + earlycon_kgdboc= [KGDB,HW]
> > + If the boot console provides the ability to read
> > + characters and can work in polling mode, you can use
> > + this parameter to tell kgdb to use it as a backend
> > + until the normal console is registered. Intended to
> > + be used together with the kgdboc parameter which
> > + specifies the normal console to transition to.
> > +
> > + The the name of the early console should be specified
> > + as the value of this parameter. Note that the name of
> > + the early console might be different than the tty
> > + name passed to kgdboc. If only one boot console with
> > + a read() function is enabled it's OK to leave the
> > + value blank and the first boot console that implements
> > + read() will be picked.
>
> There's no need for the "If only one boot console with a read()
> funcuiton is enabled" here,
>
> Seeing this in alphabetic order in this patch it also crosses my mind
> that kgdboc_earlycon might be a better name so that is sorts closer
> to the other kgdb options. This is a kgdboc feature that uses earlycon
> not an earlycon feature that uses kgdboc.
OK. 'git format-patch', sed, and 'git am' for the win.
> > +
> > earlyprintk= [X86,SH,ARM,M68k,S390]
> > earlyprintk=vga
> > earlyprintk=sclp
> > @@ -1190,6 +1206,10 @@
> > This is designed to be used in conjunction with
> > the boot argument: earlyprintk=vga
> >
> > + This parameter works in place of the kgdboc parameter
> > + but can only be used if the backing tty is available
> > + very early in the boot process.
> > +
>
> I wonder if pragmatic advice is more useful:
>
> For early debugging via a serial port see earlycon_kgdboc instead.
Done.
> > edd= [EDD]
> > Format: {"off" | "on" | "skip[mbr]"}
> >
> > diff --git a/Documentation/dev-tools/kgdb.rst b/Documentation/dev-tools/kgdb.rst
> > index d38be58f872a..c0b321403d9a 100644
> > --- a/Documentation/dev-tools/kgdb.rst
> > +++ b/Documentation/dev-tools/kgdb.rst
> > @@ -274,6 +274,20 @@ don't like this are to hack gdb to send the :kbd:`SysRq-G` for you as well as
> > on the initial connect, or to use a debugger proxy that allows an
> > unmodified gdb to do the debugging.
> >
> > +Kernel parameter: ``earlycon_kgdboc``
> > +-------------------------------------
> > +
> > +If you specify the kernel parameter ``earlycon_kgdboc`` and your serial
> > +driver registers a boot console that supports polling (doesn't need
> > +interrupts and implements a nonblocking read() function) kgdb will attempt
> > +to work using the boot console until it can transition to the regular
> > +tty driver specified by the ``kgdboc`` parameter.
> > +
> > +Normally there is only one boot console (especially that implements the
> > +read() function) so just adding ``earlycon_kgdboc`` on its own is
> > +sufficient to make this work. If you have more than one boot console you
> > +can add the boot console's name to differentiate.
> > +
>
> I think we need an example here. The example in the patch header for
> the previous patch was useful (at least for me).
Done.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2020-04-28 21:33 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-04-21 21:14 [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Douglas Anderson
2020-04-21 21:14 ` [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter Douglas Anderson
2020-04-27 16:46 ` Daniel Thompson
2020-04-28 21:32 ` Doug Anderson
2020-04-23 13:50 ` [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Greg KH
2020-04-24 8:32 ` Sumit Garg
2020-04-24 10:13 ` Daniel Thompson
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