[patch 095/198] x86_64: Keep only a single debug notifier chain

From: akpm
Date: Tue Apr 12 2005 - 14:25:41 EST



From: "Andi Kleen" <ak@xxxxxxx>

Calling a notifier three times in the debug handler does not make much sense,
because a debugger can figure out the various conditions by itself. Remove
the additional calls to DIE_DEBUG and DIE_DEBUGSTEP completely.

This matches what i386 does now.

This also makes sure interrupts are always still disabled when calling a
debugger, which prevents:

BUG: using smp_processor_id() in preemptible [00000001] code: tpopf/1470
caller is post_kprobe_handler+0x9/0x70

Call Trace:<ffffffff8024f10f>{smp_processor_id+191} <ffffffff80120e69>{post_kpro
be_handler+9}
<ffffffff80120f7a>{kprobe_exceptions_notify+58}
<ffffffff80144fc0>{notifier_call_chain+32} <ffffffff80110daf>{do_debug+335}
<ffffffff8010f513>{debug+127} <EOE>

on preemptible debug kernels with kprobes when single stepping in user space.

This was probably a bug even on non preempt kernels, this function was
supposed to be running with interrupts off according to a comment there.

Note to third part debugger maintainers: please double check your debugger can
still single step.

Cc: <prasanna@xxxxxxxxxx>
Cc: <jbeulich@xxxxxxxxxx>
Cc: <kaos@xxxxxxx>
Cc: <jim.houston@xxxxxxxx>
Cc: <jfv@xxxxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

25-akpm/arch/x86_64/kernel/traps.c | 14 +++-----------
25-akpm/include/asm-x86_64/kdebug.h | 1 -
2 files changed, 3 insertions(+), 12 deletions(-)

diff -puN arch/x86_64/kernel/traps.c~x86_64-keep-only-a-single-debug-notifier-chain arch/x86_64/kernel/traps.c
--- 25/arch/x86_64/kernel/traps.c~x86_64-keep-only-a-single-debug-notifier-chain 2005-04-12 03:21:25.729225464 -0700
+++ 25-akpm/arch/x86_64/kernel/traps.c 2005-04-12 03:21:25.734224704 -0700
@@ -659,9 +659,9 @@ asmlinkage void do_debug(struct pt_regs
asm("movq %%db6,%0" : "=r" (condition));

if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
- SIGTRAP) == NOTIFY_STOP) {
+ SIGTRAP) == NOTIFY_STOP)
return;
- }
+
conditional_sti(regs);

/* Mask out spurious debug traps due to lazy DR7 setting */
@@ -674,9 +674,7 @@ asmlinkage void do_debug(struct pt_regs
tsk->thread.debugreg6 = condition;

/* Mask out spurious TF errors due to lazy TF clearing */
- if ((condition & DR_STEP) &&
- (notify_die(DIE_DEBUGSTEP, "debugstep", regs, condition,
- 1, SIGTRAP) != NOTIFY_STOP)) {
+ if (condition & DR_STEP) {
/*
* The TF error should be masked out only if the current
* process is not traced and if the TRAP flag has been set
@@ -711,16 +709,10 @@ asmlinkage void do_debug(struct pt_regs
force_sig_info(SIGTRAP, &info, tsk);
clear_dr7:
asm volatile("movq %0,%%db7"::"r"(0UL));
- notify_die(DIE_DEBUG, "debug", regs, condition, 1, SIGTRAP);
return;

clear_TF_reenable:
set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
-
-clear_TF:
- /* RED-PEN could cause spurious errors */
- if (notify_die(DIE_DEBUG, "debug2", regs, condition, 1, SIGTRAP)
- != NOTIFY_STOP)
regs->eflags &= ~TF_MASK;
}

diff -puN include/asm-x86_64/kdebug.h~x86_64-keep-only-a-single-debug-notifier-chain include/asm-x86_64/kdebug.h
--- 25/include/asm-x86_64/kdebug.h~x86_64-keep-only-a-single-debug-notifier-chain 2005-04-12 03:21:25.730225312 -0700
+++ 25-akpm/include/asm-x86_64/kdebug.h 2005-04-12 03:21:25.734224704 -0700
@@ -23,7 +23,6 @@ enum die_val {
DIE_OOPS = 1,
DIE_INT3,
DIE_DEBUG,
- DIE_DEBUGSTEP,
DIE_PANIC,
DIE_NMI,
DIE_DIE,
_
-
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