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SubjectRe: [Patch 11/11] ftrace plugin for kernel symbol tracing using HW Breakpoint interfaces - v2
On Fri, Mar 20, 2009 at 10:04:52AM +0100, Frederic Weisbecker wrote:
> On Fri, Mar 20, 2009 at 05:20:32AM +0530, K.Prasad wrote:
> > This patch adds an ftrace plugin to detect and profile memory access over
> > kernel variables. It uses HW Breakpoint interfaces to 'watch memory
> > addresses.
> >
> > Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> > ---
> > kernel/trace/Kconfig | 21 +
> > kernel/trace/Makefile | 1
> > kernel/trace/trace.h | 25 +
> > kernel/trace/trace_ksym.c | 555 ++++++++++++++++++++++++++++++++++++++++++
> > kernel/trace/trace_selftest.c | 36 ++
> > 5 files changed, 638 insertions(+)
> >

> > +
> > +void ksym_collect_stats(unsigned long hbkpt_hit_addr)
> > +{
> > + struct hlist_node *node;
> > + struct trace_ksym *entry;
> > +
> > + spin_lock(&ksym_stat_lock);
>
>
> I see that can be called from ksym_hbkpt_handler which in turn
> can be called from interrupt context, right?
> You can issue a deadlock if you don't disable interrupts here.
>
> Thanks,
> Frederic.
>

ksym_collect_stats<--ksym_hbkpt_handler<--hw_breakpoint_handler<--do_debug
invocation happens with interrupts enabled (IF bit is set). I do find
that a few plugins in kernel/trace enclose the
trace_buffer_lock_reserve()--trace_buffer_unlock_commit() invocation
within interrupt-disabled code. Is that a requirement there?

The potential deadlock scenario you foresee isn't obvious to me. Can you
explain?

Thanks,
K.Prasad



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