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Subject[PATCH -tip v8 23/26] kprobes/x86: Remove unneeded preempt_disable/enable in interrupt handlers
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Since the int3 itself disables the local_irq and kprobes
keeps it disabled while the single step has done, the
kernel preemption never happen while processing a kprobe.
This means that we don't need to disable/enable preemption.
Also, this changes kprobe_int3_handler to use goto-out style.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
arch/x86/kernel/kprobes/core.c | 24 +++++++-----------------
1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 4767fda..8ef676f 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -506,7 +506,6 @@ static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
* stepping.
*/
regs->ip = (unsigned long)p->ainsn.insn;
- preempt_enable_no_resched();
return;
}
#endif
@@ -575,13 +574,6 @@ int kprobe_int3_handler(struct pt_regs *regs)
struct kprobe_ctlblk *kcb;

addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
- /*
- * We don't want to be preempted for the entire
- * duration of kprobe processing. We conditionally
- * re-enable preemption at the end of this function,
- * and also in reenter_kprobe() and setup_singlestep().
- */
- preempt_disable();

kcb = get_kprobe_ctlblk();
p = get_kprobe(addr);
@@ -589,7 +581,7 @@ int kprobe_int3_handler(struct pt_regs *regs)
if (p) {
if (kprobe_running()) {
if (reenter_kprobe(p, regs, kcb))
- return 1;
+ goto handled;
} else {
set_current_kprobe(p, regs, kcb);
kcb->kprobe_status = KPROBE_HIT_ACTIVE;
@@ -604,7 +596,7 @@ int kprobe_int3_handler(struct pt_regs *regs)
*/
if (!p->pre_handler || !p->pre_handler(p, regs))
setup_singlestep(p, regs, kcb, 0);
- return 1;
+ goto handled;
}
} else if (*addr != BREAKPOINT_INSTRUCTION) {
/*
@@ -617,19 +609,20 @@ int kprobe_int3_handler(struct pt_regs *regs)
* the original instruction.
*/
regs->ip = (unsigned long)addr;
- preempt_enable_no_resched();
- return 1;
+ goto handled;
} else if (kprobe_running()) {
p = __this_cpu_read(current_kprobe);
if (p->break_handler && p->break_handler(p, regs)) {
if (!skip_singlestep(p, regs, kcb))
setup_singlestep(p, regs, kcb, 0);
- return 1;
+ goto handled;
}
} /* else: not a kprobe fault; let the kernel handle it */

- preempt_enable_no_resched();
return 0;
+
+handled:
+ return 1;
}
NOKPROBE_SYMBOL(kprobe_int3_handler);

@@ -894,7 +887,6 @@ int kprobe_debug_handler(struct pt_regs *regs)
}
reset_current_kprobe();
out:
- preempt_enable_no_resched();

/*
* if somebody else is singlestepping across a probe point, flags
@@ -927,7 +919,6 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
restore_previous_kprobe(kcb);
else
reset_current_kprobe();
- preempt_enable_no_resched();
} else if (kcb->kprobe_status == KPROBE_HIT_ACTIVE ||
kcb->kprobe_status == KPROBE_HIT_SSDONE) {
/*
@@ -1058,7 +1049,6 @@ int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
memcpy((kprobe_opcode_t *)(kcb->jprobe_saved_sp),
kcb->jprobes_stack,
MIN_STACK_SIZE(kcb->jprobe_saved_sp));
- preempt_enable_no_resched();
return 1;
}
return 0;



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