Re: [PATCH 1/1] function tracing: fix wrong position computing ofstack_trace

[Wang Liming]

Ingo Molnar wrote:
> * Liming Wang <liming.wang@xxxxxxxxxxxxx> wrote:
>
> > Impact: make output of stack_trace complete if buffer overflow
> >
> > When read buffer overflows, the output of stack_trace isn't 
> > complete.
> >
> > When printing records with seq_printf in t_show, if the read buffer 
> > has overflowed by the current record, then this record won't be 
> > printed to user space through read buffer, it will just be dropped 
> > in this printing.
> >
> > When next printing, t_start should return the "*pos"th record, which 
> > is the one dropped by previous printing, but it just returns 
> > (m->private + *pos)th record.
> >
> > Here we use a more sane method to implement seq_operations which can 
> > be found in kernel code. Thus we needn't initialize m->private.
> >
> > About testing, it's not easy to overflow read buffer, but we can use 
> > seq_printf to print more padding bytes in t_show, then it's easy to 
> > check whether or not records are lost.
> >
> > This commit has been tested on both condition of overflow and non 
> > overflow.
> >
> > Signed-off-by: Liming Wang <liming.wang@xxxxxxxxxxxxx>
> > ---
> >  kernel/trace/trace_stack.c |   24 +++++++++++++++---------
> >  1 files changed, 15 insertions(+), 9 deletions(-)
>
> applied to tip/tracing/urgent, thanks!
>
> Note, i changed 'buffer overflow' to 'buffer overrun'. (buffer 
> overflow is a term typically used in a security context)
OK.

> > -	i++;
> > +	if (v == SEQ_START_TOKEN )
> > +		i = 0;
> > +	else {
> > +		i = *(long *)v;
> > +		i++;
> > +	}
>
> i also fixed these two minor style problems pointed out by 
> scripts/checkpatch.pl:
>
> | ERROR: space prohibited before that close parenthesis ')'
> | #47: FILE: kernel/trace/trace_stack.c:187:
> | +	if (v == SEQ_START_TOKEN )
> |
> | ERROR: space prohibited before that close parenthesis ')'
> | #82: FILE: kernel/trace/trace_stack.c:245:
> | +	if (v == SEQ_START_TOKEN ) {
> |
> | total: 2 errors, 0 warnings, 0 checks, 64 lines checked
It's my fault, thanks a lot!

walimis
> 	Ingo

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