08 Apr, 2014
1 commit
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This patch is a continuation of efforts trying to optimize find_vma(),
avoiding potentially expensive rbtree walks to locate a vma upon faults.
The original approach (https://lkml.org/lkml/2013/11/1/410), where the
largest vma was also cached, ended up being too specific and random,
thus further comparison with other approaches were needed. There are
two things to consider when dealing with this, the cache hit rate and
the latency of find_vma(). Improving the hit-rate does not necessarily
translate in finding the vma any faster, as the overhead of any fancy
caching schemes can be too high to consider.We currently cache the last used vma for the whole address space, which
provides a nice optimization, reducing the total cycles in find_vma() by
up to 250%, for workloads with good locality. On the other hand, this
simple scheme is pretty much useless for workloads with poor locality.
Analyzing ebizzy runs shows that, no matter how many threads are
running, the mmap_cache hit rate is less than 2%, and in many situations
below 1%.The proposed approach is to replace this scheme with a small per-thread
cache, maximizing hit rates at a very low maintenance cost.
Invalidations are performed by simply bumping up a 32-bit sequence
number. The only expensive operation is in the rare case of a seq
number overflow, where all caches that share the same address space are
flushed. Upon a miss, the proposed replacement policy is based on the
page number that contains the virtual address in question. Concretely,
the following results are seen on an 80 core, 8 socket x86-64 box:1) System bootup: Most programs are single threaded, so the per-thread
scheme does improve ~50% hit rate by just adding a few more slots to
the cache.+----------------+----------+------------------+
| caching scheme | hit-rate | cycles (billion) |
+----------------+----------+------------------+
| baseline | 50.61% | 19.90 |
| patched | 73.45% | 13.58 |
+----------------+----------+------------------+2) Kernel build: This one is already pretty good with the current
approach as we're dealing with good locality.+----------------+----------+------------------+
| caching scheme | hit-rate | cycles (billion) |
+----------------+----------+------------------+
| baseline | 75.28% | 11.03 |
| patched | 88.09% | 9.31 |
+----------------+----------+------------------+3) Oracle 11g Data Mining (4k pages): Similar to the kernel build workload.
+----------------+----------+------------------+
| caching scheme | hit-rate | cycles (billion) |
+----------------+----------+------------------+
| baseline | 70.66% | 17.14 |
| patched | 91.15% | 12.57 |
+----------------+----------+------------------+4) Ebizzy: There's a fair amount of variation from run to run, but this
approach always shows nearly perfect hit rates, while baseline is just
about non-existent. The amounts of cycles can fluctuate between
anywhere from ~60 to ~116 for the baseline scheme, but this approach
reduces it considerably. For instance, with 80 threads:+----------------+----------+------------------+
| caching scheme | hit-rate | cycles (billion) |
+----------------+----------+------------------+
| baseline | 1.06% | 91.54 |
| patched | 99.97% | 14.18 |
+----------------+----------+------------------+[akpm@linux-foundation.org: fix nommu build, per Davidlohr]
[akpm@linux-foundation.org: document vmacache_valid() logic]
[akpm@linux-foundation.org: attempt to untangle header files]
[akpm@linux-foundation.org: add vmacache_find() BUG_ON]
[hughd@google.com: add vmacache_valid_mm() (from Oleg)]
[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: adjust and enhance comments]
Signed-off-by: Davidlohr Bueso
Reviewed-by: Rik van Riel
Acked-by: Linus Torvalds
Reviewed-by: Michel Lespinasse
Cc: Oleg Nesterov
Tested-by: Hugh Dickins
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
26 Feb, 2014
1 commit
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The function kgdb_breakpoint() sets up break point at
compile time by calling arch_kgdb_breakpoint();
Though this call is surrounded by wmb() barrier,
the compile can still re-order the break point,
because this scheduling barrier is not a code motion
barrier in gcc.Making kgdb_breakpoint() as noinline solves this problem
of code reording around break point instruction and also
avoids problem of being called as inline function from
other placesMore details about discussion on this can be found here
http://comments.gmane.org/gmane.linux.ports.arm.kernel/269732Signed-off-by: Vijaya Kumar K
Acked-by: Will Deacon
Acked-by: Jason Wessel
Signed-off-by: Catalin Marinas
25 Jan, 2014
1 commit
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Some code added to the debug_core module had KDB dependencies
that it shouldn't have. Move the KDB dependent REASON back to
the caller to remove the dependency in the debug core code.Update the call from the UV NMI handler to conform to the new
interface.Signed-off-by: Mike Travis
Reviewed-by: Hedi Berriche
Cc: Russ Anderson
Cc: Jason Wessel
Cc: Peter Zijlstra
Cc: Paul Mackerras
Cc: Arnaldo Carvalho de Melo
Link: http://lkml.kernel.org/r/20140114162551.318251993@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar
04 Oct, 2013
1 commit
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This patch adds a kgdb_nmicallin() interface that can be used by
external NMI handlers to call the KGDB/KDB handler. The primary
need for this is for those types of NMI interrupts where all the
CPUs have already received the NMI signal. Therefore no
send_IPI(NMI) is required, and in fact it will cause a 2nd
unhandled NMI to occur. This generates the "Dazed and Confuzed"
messages.Since all the CPUs are getting the NMI at roughly the same time,
it's not guaranteed that the first CPU that hits the NMI handler
will manage to enter KGDB and set the dbg_master_lock before the
slaves start entering. The new argument "send_ready" was added
for KGDB to signal the NMI handler to release the slave CPUs for
entry into KGDB.Signed-off-by: Mike Travis
Acked-by: Jason Wessel
Reviewed-by: Dimitri Sivanich
Reviewed-by: Hedi Berriche
Cc: Peter Zijlstra
Cc: Paul Mackerras
Cc: Arnaldo Carvalho de Melo
Link: http://lkml.kernel.org/r/20131002151417.928886849@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar
01 May, 2013
1 commit
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Currently help message of /proc/sysrq-trigger highlight its upper-case
characters, like below:SysRq : HELP : loglevel(0-9) reBoot Crash terminate-all-tasks(E)
memory-full-oom-kill(F) kill-all-tasks(I) ...this would confuse user trigger sysrq by upper-case character, which is
inconsistent with the real lower-case character registed key.This inconsistent help message will also lead more confused when
26 upper-case letters put into use in future.This patch fix kgdb sysrq key: "debug(g)"
Signed-off-by: zhangwei(Jovi)
Cc: Jason Wessel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
03 Mar, 2013
1 commit
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Pull KGDB/KDB fixes and cleanups from Jason Wessel:
"For a change we removed more code than we added. If people aren't
using it we shouldn't be carrying it. :-)Cleanups:
- Remove kdb ssb command - there is no in kernel disassembler to
support it- Remove kdb ll command - Always caused a kernel oops and there were
no bug reports so no one was using this command- Use kernel ARRAY_SIZE macro instead of array computations
Fixes:
- Stop oops in kdb if user executes kdb_defcmd with args- kdb help command truncated text
- ppc64 support for kgdbts
- Add missing kconfig option from original kdb port for dealing with
catastrophic kernel crashes such that you can reboot automatically
on continue from kdb"* tag 'for_linux-3.9' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb:
kdb: Remove unhandled ssb command
kdb: Prevent kernel oops with kdb_defcmd
kdb: Remove the ll command
kdb_main: fix help print
kdb: Fix overlap in buffers with strcpy
Fixed dead ifdef block by adding missing Kconfig option.
kdb: Setup basic kdb state before invoking commands via kgdb
kdb: use ARRAY_SIZE where possible
kgdb/kgdbts: support ppc64
kdb: A fix for kdb command table expansion
02 Mar, 2013
8 commits
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The 'ssb' command can only be handled when we have a disassembler, to check for
branches, so remove the 'ssb' command for now.Signed-off-by: Vincent Stehlé
Signed-off-by: Jason Wessel -
The kdb_defcmd can only be used to display the available command aliases
while using the kernel debug shell. If you try to define a new macro
while the kernel debugger is active it will oops. The debug shell
macros must use pre-allocated memory set aside at the time kdb_init()
is run, and the kdb_defcmd is restricted to only working at the time
that the kdb_init sequence is being run, which only occurs if you
actually activate the kernel debugger.Signed-off-by: Jason Wessel
-
Recently some code inspection was done after fixing a problem with
kmalloc used while in the kernel debugger context (which is not
legal), and it turned up the fact that kdb ll command will oops the
kernel.Given that there have been zero bug reports on the command combined
with the fact it will oops the kernel it is clearly not being used.
Instead of fixing it, it will be removed.Signed-off-by: Jason Wessel
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The help command was chopping all the usage instructions such that
they were not readable.Example:
bta [D|R|S|T|C|Z|E|U|I| Backtrace all processes matching state flag
per_cpu [] [ [] []
Display per_cpu variablesAll that is needed is to check the how long the cmd_usage is and jump
to the next line when appropriate.Signed-off-by: Jason Wessel
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Maxime reported that strcpy(s->usage, s->usage+1) has no definitive
guarantee that it will work on all archs the same way when you have
overlapping memory. The fix is simple for the kdb code because we
still have the original string memory in the function scope, so we
just have to use that as the argument instead.Reported-by: Maxime Villard
Signed-off-by: Jason Wessel -
Although invasive kdb commands are not supported via kgdb, some useful
non-invasive commands like bt* require basic kdb state to be setup before
calling into the kdb code. Factor out some of this code and call it before
and after executing kdb commands via kgdb.Signed-off-by: Matt Klein
Signed-off-by: Jason Wessel -
Signed-off-by: Sasha Levin
Signed-off-by: Jason Wessel -
When locally adding in some additional kdb commands, I stumbled
across an issue with the dynamic expansion of the kdb command table.
When the number of kdb commands exceeds the size of the statically
allocated kdb_base_commands[] array, additional space is allocated in
the kdb_register_repeat() routine.The unused portion of the newly allocated array was not being initialized
to zero properly and this would result in segfaults when help '?' was
executed or when a search for a non-existing command would traverse the
command table beyond the end of valid command entries and then attempt
to use the non-zeroed area as actual command entries.Signed-off-by: John Blackwood
Signed-off-by: Jason Wessel
05 Feb, 2013
1 commit
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There's no reason kgdb.h itself needs to include the 8250 serial port
header file. So push it down to the _very_ limited number of individual
drivers that need the values in that file, and fix up the places where
people really wanted serial_core.h and platform_device.h.Signed-off-by: Greg Kroah-Hartman
12 Jan, 2013
1 commit
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You should never look at such a module, so it's excised from all paths
which traverse the modules list.We add the state at the end, to avoid gratuitous ABI break (ksplice).
Signed-off-by: Rusty Russell
13 Oct, 2012
1 commit
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Pull KGDB/KDB fixes and cleanups from Jason Wessel:
"Cleanups
- Clean up compile warnings in kgdboc.c and x86/kernel/kgdb.c
- Add module event hooks for simplified debugging with gdb
Fixes
- Fix kdb to stop paging with 'q' on bta and dmesg
- Fix for data that scrolls off the vga console due to line wrapping
when using the kdb pager
New
- The debug core registers for kernel module events which allows a
kernel aware gdb to automatically load symbols and break on entry
to a kernel module
- Allow kgdboc=kdb to setup kdb on the vga console"* tag 'for_linus-3.7' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb:
tty/console: fix warnings in drivers/tty/serial/kgdboc.c
kdb,vt_console: Fix missed data due to pager overruns
kdb: Fix dmesg/bta scroll to quit with 'q'
kgdboc: Accept either kbd or kdb to activate the vga + keyboard kdb shell
kgdb,x86: fix warning about unused variable
mips,kgdb: fix recursive page fault with CONFIG_KPROBES
kgdb: Add module event hooks
12 Oct, 2012
3 commits
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It is possible to miss data when using the kdb pager. The kdb pager
does not pay attention to the maximum column constraint of the screen
or serial terminal. This result is not incrementing the shown lines
correctly and the pager will print more lines that fit on the screen.
Obviously that is less than useful when using a VGA console where you
cannot scroll back.The pager will now look at the kdb_buffer string to see how many
characters are printed. It might not be perfect considering you can
output ASCII that might move the cursor position, but it is a
substantially better approximation for viewing dmesg and trace logs.This also means that the vt screen needs to set the kdb COLUMNS
variable.Cc:
Signed-off-by: Jason Wessel -
If you press 'q' the pager should exit instead of printing everything
from dmesg which can really bog down a 9600 baud serial link.The same is true for the bta command.
Signed-off-by: Jason Wessel
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Allow gdb to auto load kernel modules when it is attached,
which makes it trivially easy to debug module init functions
or pre-set breakpoints in a kernel module that has not loaded yet.Signed-off-by: Jason Wessel
27 Sep, 2012
2 commits
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This command disables NMI-entry. If NMI source has been previously shared
with a serial console ("debug port"), this effectively releases the port
from KDB exclusive use, and makes the console available for normal use.Of course, NMI can be reenabled, enable_nmi modparam is used for that:
echo 1 > /sys/module/kdb/parameters/enable_nmi
Signed-off-by: Anton Vorontsov
Acked-by: Jason Wessel
Signed-off-by: Greg Kroah-Hartman -
The new arch callback should manage NMIs that usually cause KGDB to
enter. That is, not all NMIs should be enabled/disabled, but only
those that issue kgdb_handle_exception().We must mask it as serial-line interrupt can be used as an NMI, so
if the original KGDB-entry cause was say a breakpoint, then every
input to KDB console will cause KGDB to reenter, which we don't want.Signed-off-by: Anton Vorontsov
Acked-by: Jason Wessel
Signed-off-by: Greg Kroah-Hartman
31 Jul, 2012
3 commits
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Currently kernel never set KGDB_REASON_NMI. We do now, when we enter
KGDB/KDB from an NMI.This is not to be confused with kgdb_nmicallback(), NMI callback is
an entry for the slave CPUs during CPUs roundup, but REASON_NMI is the
entry for the master CPU.Signed-off-by: Anton Vorontsov
Signed-off-by: Jason Wessel -
Having the CPU in the more prompt is completely redundent vs the
standard kdb prompt, and it also wastes 32 bytes on the stack.Signed-off-by: Jason Wessel
-
This code cleanup was missed in the original kdb merge, and this code
is simply not used at all. The code that was previously used to set
the KDB_FLAG_ONLY_DO_DUMP was removed prior to the initial kdb merge.Signed-off-by: Jason Wessel
22 Jul, 2012
3 commits
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The locked variants are prone to deadlocks (suppose we got to the
debugger w/ the logbuf lock held), so let's switch to nolock variants.Signed-off-by: Anton Vorontsov
Signed-off-by: Linus Torvalds -
The function is no longer needed, so remove it.
Signed-off-by: Anton Vorontsov
Signed-off-by: Linus Torvalds -
The kgdb dmesg command is broken after the printk rework. The old logic
in kdb code makes no sense in terms of current printk/logging storage
format, and KDB simply hangs forever.This patch revives the command by switching to kmsg_dumper iterator.
The code is now much more simpler and shorter.
Signed-off-by: Anton Vorontsov
Signed-off-by: Linus Torvalds
05 Apr, 2012
1 commit
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Pull KGDB/KDB regression fixes from Jason Wessel:
- Fix a Smatch warning that appeared in the 3.4 merge window
- Fix kgdb test suite with SMP for all archs without HW single stepping
- Fix kgdb sw breakpoints with CONFIG_DEBUG_RODATA=y limitations on x86
- Fix oops on kgdb test suite with CONFIG_DEBUG_RODATA
- Fix kgdb test suite with SMP for all archs with HW single stepping* tag 'for_linus-3.4-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb:
x86,kgdb: Fix DEBUG_RODATA limitation using text_poke()
kgdb,debug_core: pass the breakpoint struct instead of address and memory
kgdbts: (2 of 2) fix single step awareness to work correctly with SMP
kgdbts: (1 of 2) fix single step awareness to work correctly with SMP
kgdbts: Fix kernel oops with CONFIG_DEBUG_RODATA
kdb: Fix smatch warning on dbg_io_ops->is_console
30 Mar, 2012
2 commits
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There is extra state information that needs to be exposed in the
kgdb_bpt structure for tracking how a breakpoint was installed. The
debug_core only uses the the probe_kernel_write() to install
breakpoints, but this is not enough for all the archs. Some arch such
as x86 need to use text_poke() in order to install a breakpoint into a
read only page.Passing the kgdb_bpt structure to kgdb_arch_set_breakpoint() and
kgdb_arch_remove_breakpoint() allows other archs to set the type
variable which indicates how the breakpoint was installed.Cc: stable@vger.kernel.org # >= 2.6.36
Signed-off-by: Jason Wessel -
The Smatch tool warned that the change from commit b8adde8dd
(kdb: Avoid using dbg_io_ops until it is initialized) should
add another null check later in the kdb_printf().It is worth noting that the second use of dbg_io_ops->is_console
is protected by the KDB_PAGER state variable which would only
get set when kdb is fully active and initialized. If we
ever encounter changes or defects in the KDB_PAGER state
we do not want to crash the kernel in a kdb_printf/printk.CC: Tim Bird
Reported-by: Dan Carpenter
Signed-off-by: Jason Wessel
29 Mar, 2012
2 commits
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…m/linux/kernel/git/dhowells/linux-asm_system
Pull "Disintegrate and delete asm/system.h" from David Howells:
"Here are a bunch of patches to disintegrate asm/system.h into a set of
separate bits to relieve the problem of circular inclusion
dependencies.I've built all the working defconfigs from all the arches that I can
and made sure that they don't break.The reason for these patches is that I recently encountered a circular
dependency problem that came about when I produced some patches to
optimise get_order() by rewriting it to use ilog2().This uses bitops - and on the SH arch asm/bitops.h drags in
asm-generic/get_order.h by a circuituous route involving asm/system.h.The main difficulty seems to be asm/system.h. It holds a number of
low level bits with no/few dependencies that are commonly used (eg.
memory barriers) and a number of bits with more dependencies that
aren't used in many places (eg. switch_to()).These patches break asm/system.h up into the following core pieces:
(1) asm/barrier.h
Move memory barriers here. This already done for MIPS and Alpha.
(2) asm/switch_to.h
Move switch_to() and related stuff here.
(3) asm/exec.h
Move arch_align_stack() here. Other process execution related bits
could perhaps go here from asm/processor.h.(4) asm/cmpxchg.h
Move xchg() and cmpxchg() here as they're full word atomic ops and
frequently used by atomic_xchg() and atomic_cmpxchg().(5) asm/bug.h
Move die() and related bits.
(6) asm/auxvec.h
Move AT_VECTOR_SIZE_ARCH here.
Other arch headers are created as needed on a per-arch basis."
Fixed up some conflicts from other header file cleanups and moving code
around that has happened in the meantime, so David's testing is somewhat
weakened by that. We'll find out anything that got broken and fix it..* tag 'split-asm_system_h-for-linus-20120328' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-asm_system: (38 commits)
Delete all instances of asm/system.h
Remove all #inclusions of asm/system.h
Add #includes needed to permit the removal of asm/system.h
Move all declarations of free_initmem() to linux/mm.h
Disintegrate asm/system.h for OpenRISC
Split arch_align_stack() out from asm-generic/system.h
Split the switch_to() wrapper out of asm-generic/system.h
Move the asm-generic/system.h xchg() implementation to asm-generic/cmpxchg.h
Create asm-generic/barrier.h
Make asm-generic/cmpxchg.h #include asm-generic/cmpxchg-local.h
Disintegrate asm/system.h for Xtensa
Disintegrate asm/system.h for Unicore32 [based on ver #3, changed by gxt]
Disintegrate asm/system.h for Tile
Disintegrate asm/system.h for Sparc
Disintegrate asm/system.h for SH
Disintegrate asm/system.h for Score
Disintegrate asm/system.h for S390
Disintegrate asm/system.h for PowerPC
Disintegrate asm/system.h for PA-RISC
Disintegrate asm/system.h for MN10300
... -
Remove all #inclusions of asm/system.h preparatory to splitting and killing
it. Performed with the following command:perl -p -i -e 's!^#\s*include\s*.*\n!!' `grep -Irl '^#\s*include\s*' *`
Signed-off-by: David Howells
24 Mar, 2012
1 commit
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Pull KGDB/KDB updates from Jason Wessel:
"Fixes:
- Fix KDB keyboard repeat scan codes and leaked keyboard events
- Fix kernel crash with kdb_printf() for users who compile new
kdb_printf()'s in early code
- Return all segment registers to gdb on x86_64Features:
- KDB/KGDB hook the reboot notifier and end user can control if it
stops, detaches or does nothing (updated docs as well)
- Notify users who use CONFIG_DEBUG_RODATA to use hw breakpoints"* tag 'for_linus-3.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb:
kdb: Add message about CONFIG_DEBUG_RODATA on failure to install breakpoint
kdb: Avoid using dbg_io_ops until it is initialized
kgdb,debug_core: add the ability to control the reboot notifier
KDB: Fix usability issues relating to the 'enter' key.
kgdb,debug-core,gdbstub: Hook the reboot notifier for debugger detach
kgdb: Respect that flush op is optional
kgdb: x86: Return all segment registers also in 64-bit mode
23 Mar, 2012
6 commits
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On x86, if CONFIG_DEBUG_RODATA is set, one cannot set breakpoints
via KDB. Apparently this is a well-known problem, as at least one distribution
now ships with both KDB enabled and CONFIG_DEBUG_RODATA=y for security reasons.This patch adds an printk message to the breakpoint failure case,
in order to provide suggestions about how to use the debugger.Reported-by: Tim Bird
Signed-off-by: Jason Wessel
Acked-by: Tim Bird -
This fixes a bug with setting a breakpoint during kdb initialization
(from kdb_cmds). Any call to kdb_printf() before the initialization
of the kgdboc serial console driver (which happens much later during
bootup than kdb_init), results in kernel panic due to the use of
dbg_io_ops before it is initialized.Signed-off-by: Tim Bird
Signed-off-by: Jason Wessel -
Sometimes it is desirable to stop the kernel debugger before allowing
a system to reboot either with kdb or kgdb. This patch adds the
ability to turn the reboot notifier on and off or enter the debugger
and stop kernel execution before rebooting.It is possible to change the setting after booting the kernel with the
following:echo 1 > /sys/module/debug_core/parameters/kgdbreboot
It is also possible to change this setting using kdb / kgdb to
manipulate the variable directly.Using KDB:
mm kgdbreboot 1Using gdb:
set kgdbreboot=1Reported-by: Jan Kiszka
Signed-off-by: Jason Wessel -
This fixes the following problems:
1) Typematic-repeat of 'enter' gives warning message
and leaks make/break if KDB exits. Repeats
look something like 0x1c 0x1c .... 0x9c
2) Use of 'keypad enter' gives warning message and
leaks the ENTER break/make code out if KDB exits.
KP ENTER repeats look someting like 0xe0 0x1c
0xe0 0x1c ... 0xe0 0x9c.
3) Lag on the order of seconds between "break" and "make" when
expecting the enter "break" code. Seen under virtualized
environments such as VMware ESX.The existing special enter handler tries to glob the enter break code,
but this fails if the other (KP) enter was used, or if there was a key
repeat. It also fails if you mashed some keys along with enter, and
you ended up with a non-enter make or non-enter break code coming
after the enter make code. So first, we modify the handler to handle
these cases. But performing these actions on every enter is annoying
since now you can't hold ENTER down to scroll d messages in
KDB. Since this special behaviour is only necessary to handle the
exiting KDB ('g' + ENTER) without leaking scancodes to the OS. This
cleanup needs to get executed anytime the kdb_main loop exits.Tested on QEMU. Set a bp on atkbd.c to verify no scan code was leaked.
Cc: Andrei Warkentin
[jason.wessel@windriver.com: move cleanup calls to kdb_main.c]
Signed-off-by: Andrei Warkentin
Signed-off-by: Jason Wessel -
The gdbstub and kdb should get detached if the system is rebooting.
Calling gdbstub_exit() will set the proper debug core state and send a
message to any debugger that is connected to correctly detach.An attached debugger will receive the exit code from
include/linux/reboot.h based on SYS_HALT, SYS_REBOOT, etc...Reported-by: Jan Kiszka
Signed-off-by: Jason Wessel -
Not all kgdb I/O drivers implement a flush operation. Adjust
gdbstub_exit accordingly.Signed-off-by: Jan Kiszka
Signed-off-by: Jason Wessel
