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Re: [PATCH 1/2] x86: fix kprobe_handler reenable preemption
- From: Masami Hiramatsu <mhiramat at redhat dot com>
- To: Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Jim Keniston <jkenisto at us dot ibm dot com>, Ingo Molnar <mingo at elte dot hu>
- Cc: Roland McGrath <roland at redhat dot com>, prasanna at in dot ibm dot com, anil dot s dot keshavamurthy at intel dot com, davem at davemloft dot net, Harvey Harrison <harvey dot harrison at gmail dot com>, systemtap-ml <systemtap at sources dot redhat dot com>, LKML <linux-kernel at vger dot kernel dot org>, Arjan van de Ven <arjan at infradead dot org>
- Date: Tue, 18 Dec 2007 22:32:28 -0500
- Subject: Re: [PATCH 1/2] x86: fix kprobe_handler reenable preemption
- References: <4768555A.3000604@redhat.com>
Hi
Masami Hiramatsu wrote:
> Fix a preemption bug in kprobe_handler(). It has to call preempt_enable()
> before returning.
> I think this is critical on preemptive kernel.
Sorry, this patch has a mistake.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
> ---
> arch/x86/kernel/kprobes.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> Index: b/arch/x86/kernel/kprobes.c
> ===================================================================
> --- a/arch/x86/kernel/kprobes.c 2007-12-18 12:51:00.000000000 -0500
> +++ b/arch/x86/kernel/kprobes.c 2007-12-18 12:53:38.000000000 -0500
> @@ -467,7 +467,8 @@
> arch_disarm_kprobe(p);
> regs->ip = (unsigned long)p->addr;
> reset_current_kprobe();
> - return 1;
> + ret = 1;
> + goto no_kprobe;
> #endif
> }
> /* We have reentered the kprobe_handler(), since
> @@ -481,7 +482,7 @@
> kprobes_inc_nmissed_count(p);
> prepare_singlestep(p, regs);
> kcb->kprobe_status = KPROBE_REENTER;
> - return 1;
> + ret = 1;
Here, "return 1;" is correct. After single step is done, preemption is enabled
in post_kprobe_handler().
> } else {
> if (*addr != BREAKPOINT_INSTRUCTION) {
> /* The breakpoint instruction was removed by
>
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com, masami.hiramatsu.pt@hitachi.com