On an SMP system the kgdb_single_step flag has the possibility to
indefinitely hang the system in the case. Consider the case where,
CPU 1 has the schedule lock and CPU 0 is set to single step, there is
no way for CPU 0 to run another task.
The easy way to observe the problem is to make 2 cpus busy, and run
the kgdb test suite. You will see that it hangs the system very
quickly.
while [ 1 ] ; do find /proc > /dev/null 2>&1 ; done &
while [ 1 ] ; do find /proc > /dev/null 2>&1 ; done &
echo V1 > /sys/module/kgdbts/parameters/kgdbts
The side effect of this patch is that there is the possibility
to miss a breakpoint in the case that a single step operation
was executed to step over a breakpoint in common code.
The trade off of the missed breakpoint is preferred to
hanging the kernel. This can be fixed in the future by
using kprobes or another strategy to step over planted
breakpoints with out of line execution.
CC: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
It is possible for the user_mode_vm(regs) check to return true on the
i368 arch for a non master kgdb cpu or when the master kgdb cpu
handles the NMI watch dog exception.
The solution is simply to select the correct gdb_ss location
based on the check to user_mode_vm(regs).
CC: Ingo Molnar <mingo@elte.hu>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
The for loop starts with a breakno of 0, and ends when it's 4. so
this test is always true.
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
* 'x86-cleanups-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
x86: Fix a section mismatch in arch/x86/kernel/setup.c
x86: Fixup last users of irq_chip->typename
x86: Remove BKL from apm_32
x86: Remove BKL from microcode
x86: use kernel_stack_pointer() in kprobes.c
x86: use kernel_stack_pointer() in kgdb.c
x86: use kernel_stack_pointer() in dumpstack.c
x86: use kernel_stack_pointer() in process_32.c
The way to obtain a kernel-mode stack pointer from a struct
pt_regs in 32-bit mode is "subtle": the stack doesn't actually
contain the stack pointer, but rather the location where it would
have been marks the actual previous stack frame. For clarity, use
kernel_stack_pointer() instead of coding this weirdness
explicitly.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
* 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
x86, 64-bit: ifdef out struct thread_struct::ip
x86, 32-bit: ifdef out struct thread_struct::fs
x86: clean up alternative.h
This patch resets the bit in dr6 after the corresponding exception is
handled in code, so that we keep a clean track of the current virtual debug
status register.
[ Impact: keep track of breakpoints triggering completion ]
Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
The treatment of the SP register is different on x86_64 and i386.
This is a regression fix that lived outside the mainline kernel from
2.6.27 to now. The regression was a result of the original merge
consolidation of the i386 and x86_64 archs to x86.
The incorrectly reported SP on i386 prevented stack tracebacks from
working correctly in gdb.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
struct thread_struct::ip isn't used on x86_64, struct pt_regs::ip is used
instead.
kgdb should be reading 0 always, but I can't check it.
[ Impact: (potentially) reduce thread_struct size on 64-bit ]
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: containers@lists.linux-foundation.org
LKML-Reference: <20090503233015.GJ16631@x200.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Our send_IPI_*() methods and definitions are a twisted mess: the same
symbol is defined to different things depending on .config details,
in a non-transparent way.
- spread out the quirks into separately named per apic driver methods
- prefix the standard PC methods with default_
- get rid of wrapper macro obfuscation
- clean up various details
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Stress-testing KVM's latest NMI support with kgdbts inside an SMP guest,
I came across spurious unhandled NMIs while running the singlestep test.
Looking closer at the code path each NMI takes when KGDB is enabled, I
noticed that kgdb_nmicallback is called twice per event: One time via
DIE_NMI_IPI notification, the second time on DIE_NMI. Removing the first
invocation cures the unhandled NMIs here.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
On x86_64 the gdb serial register structure defines the PS (also known
as eflags), CS and SS registers as 4 bytes entities.
This patch splits the x86_64 regnames enum into a 32 and 64 version to
account for the 32 bit entities in the gdb serial packets.
Also the program counter is properly filled in for the sleeping
threads.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
On the x86 arch, user space single step exceptions should be ignored
if they occur in the kernel space, such as ptrace stepping through a
system call.
First check if it is kgdb that is executing a single step, then ensure
it is not an accidental traversal into the user space, while in kgdb,
any other time the TIF_SINGLESTEP is set, kgdb should ignore the
exception.
On x86, arm, mips and powerpc, the kgdb_contthread usage was
inconsistent with the way single stepping is implemented in the kgdb
core. The arch specific stub should always set the
kgdb_cpu_doing_single_step correctly if it is single stepping. This
allows kgdb to correctly process an instruction steps if ptrace
happens to be requesting an instruction step over a system call.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
TF_MASK is no longer defined, use X86_EFLAGS_TF.
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kgdb core fixes:
- Check to see that mm->mmap_cache is not null before calling
flush_cache_range(), else on arch=ARM it will cause a fatal
fault.
- Breakpoints should only be restored if they are in the BP_ACTIVE
state.
- Fix a typo in comments to "kgdb_register_io_module"
x86 kgdb fixes:
- Fix the x86 arch handler such that on a kill or detach that the
appropriate cleanup on the single stepping flags gets run.
- Add in the DIE_NMIWATCHDOG call for x86_64
- Touch the nmi watchdog before returning the system to normal
operation after performing any kind of kgdb operation, else
the possibility exists to trigger the watchdog.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Add HW breakpoints into the arch specific portion of x86 kgdb. In the
current x86 kernel.org kernels HW breakpoints are changed out in lazy
fashion because there is no infrastructure around changing them when
changing to a kernel task or entering the kernel mode via a system
call. This lazy approach means that if a user process uses HW
breakpoints the kgdb will loose out. This is an acceptable trade off
because the developer debugging the kernel is assumed to know what is
going on system wide and would be aware of this trade off.
There is a minor bug fix to the kgdb core so as to correctly call the
hw breakpoint functions with a valid value from the enum.
There is also a minor change to the x86_64 startup code when using
early HW breakpoints. When the debugger is connected, the cpu startup
code must not zero out the HW breakpoint registers or you cannot hit
the breakpoints you are interested in, in the first place.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This patch fixes the hang regression with kgdb when the NMI interrupt
comes in while the master core is returning from an exception.
Adjust the NMI logic such that KGDB will not stop NMI exceptions from
occurring by in general returning NOTIFY_DONE. It is not possible to
distinguish the debug NMI sync vs the normal NMI apic interrupt so
kgdb needs to catch the unknown NMI if it the debugger was previously
active on one of the cpus.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
simplified and streamlined kgdb support on x86, both 32-bit and 64-bit,
based on patch from:
Subject: kgdb: core-lite
From: Jason Wessel <jason.wessel@windriver.com>
[ and countless other authors - see the patch for details. ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
