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    SubjectRe: [PATCH 18/18] tracing/kprobes: Dump the culprit kprobe in case of kprobe recursion
    On Thu, Aug 27, 2009 at 11:30:24AM -0400, Masami Hiramatsu wrote:
    > Hi Frederic,
    >
    > Frederic Weisbecker wrote:
    > > Kprobes can enter into a probing recursion, ie: a kprobe that does an
    > > endless loop because one of its core mechanism function used during
    > > probing is also probed itself.
    > >
    > > This patch helps pinpointing the kprobe that raised such recursion
    > > by dumping it and raising a BUG instead of a warning (we also disarm
    > > the kprobe to try avoiding recursion in BUG itself). Having a BUG
    > > instead of a warning stops the stacktrace in the right place and
    > > doesn't pollute the logs with hundreds of traces that eventually end
    > > up in a stack overflow.
    >
    > Thanks, but I also found similar bug cases.
    >
    > >
    > > Signed-off-by: Frederic Weisbecker<fweisbec@gmail.com>
    > > Cc: Masami Hiramatsu<mhiramat@redhat.com>
    > > Cc: Ananth N Mavinakayanahalli<ananth@in.ibm.com>
    > > ---
    > > arch/x86/kernel/kprobes.c | 8 ++++++--
    > > include/linux/kprobes.h | 2 ++
    > > kernel/kprobes.c | 7 +++++++
    > > 3 files changed, 15 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
    > > index 16ae961..ecee3d2 100644
    > > --- a/arch/x86/kernel/kprobes.c
    > > +++ b/arch/x86/kernel/kprobes.c
    > > @@ -490,9 +490,13 @@ static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
    >
    > Before this, kprobes checks p != kprobe_running(), but it's a
    > meaningless branch. Hitting a kprobe while KPROBES_HIT_SS always
    > treated as unrecoverable.



    Yeah, but that's the place where a probe ends up when bad reentrancy happens
    right?



    > > /* A probe has been hit in the codepath leading up
    > > * to, or just after, single-stepping of a probed
    > > * instruction. This entire codepath should strictly
    > > - * reside in .kprobes.text section. Raise a warning
    > > - * to highlight this peculiar case.
    > > + * reside in .kprobes.text section.
    > > + * Raise a BUG or we'll continue in an endless
    > > + * reentering loop and eventually a stack overflow.
    > > */
    > > + arch_disarm_kprobe(p);
    > > + dump_kprobe(p);
    > > + BUG();
    > > }
    > > default:
    > > /* impossible cases */
    > > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
    > > index bcd9c07..87eb79c 100644
    > > --- a/include/linux/kprobes.h
    > > +++ b/include/linux/kprobes.h
    > > @@ -296,6 +296,8 @@ void recycle_rp_inst(struct kretprobe_instance *ri, struct hlist_head *head);
    > > int disable_kprobe(struct kprobe *kp);
    > > int enable_kprobe(struct kprobe *kp);
    > >
    > > +void dump_kprobe(struct kprobe *kp);
    > > +
    > > #else /* !CONFIG_KPROBES: */
    > >
    > > static inline int kprobes_built_in(void)
    > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
    > > index ef177d6..f72e96c 100644
    > > --- a/kernel/kprobes.c
    > > +++ b/kernel/kprobes.c
    > > @@ -1141,6 +1141,13 @@ static void __kprobes kill_kprobe(struct kprobe *p)
    > > arch_remove_kprobe(p);
    > > }
    > >
    > > +void __kprobes dump_kprobe(struct kprobe *kp)
    > > +{
    > > + printk(KERN_WARNING "Dumping kprobe:\n");
    > > + printk(KERN_WARNING "Name: %s\nAddress: %p\nOffset: %x\n",
    > > + kp->symbol_name, kp->addr, kp->offset);
    > > +}
    >
    > Since kp->symbol_name + kp->offset = kp->addr, I recommend to show it
    > as "Kprobe at %s+%x:<%p>\n", kp->symbol_name, kp->offset, kp->addr.


    Ok I'll fix this, thanks.


    > > +
    > > /* Module notifier call back, checking kprobes on the module */
    > > static int __kprobes kprobes_module_callback(struct notifier_block *nb,
    > > unsigned long val, void *data)
    >
    > Thank you,
    >
    > --
    > Masami Hiramatsu
    >
    > Software Engineer
    > Hitachi Computer Products (America), Inc.
    > Software Solutions Division
    >
    > e-mail: mhiramat@redhat.com
    >



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