Messages in this thread | | | Date | Wed, 19 Nov 2014 08:48:00 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH 2/2] tracing: Use trace_seq_used() and seq_buf_used() instead of len |
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On Wed, 19 Nov 2014 12:40:17 +0100 Petr Mladek <pmladek@suse.cz> wrote:
> > > > > > There is one more dangerous usage in trace_printk_seq(). It is on > > > three lines there. > > > > You totally confused me. What usage in trace_printk_seq(), and what > > three lines? > > > > In this patch, trace_printk_seq() looks like this: > > > > int trace_print_seq(struct seq_file *m, struct trace_seq *s) > > { > > int ret; > > > > __trace_seq_init(s); > > > > ret = seq_buf_print_seq(m, &s->seq); > > > > /* > > * Only reset this buffer if we successfully wrote to the > > * seq_file buffer. This lets the caller try again or > > * do something else with the contents. > > */ > > if (!ret) > > trace_seq_init(s); > > > > return ret; > > } > > The confusion is caused by the 'k' ("print" vs. "printk") in the > function name. I was talking about the following function from > kernel/trace/trace.c:
Silly 'k', Trix are for kids!
> > void > trace_printk_seq(struct trace_seq *s) > { > /* Probably should print a warning here. */ > if (s->seq.len >= TRACE_MAX_PRINT) > s->seq.len = TRACE_MAX_PRINT; > > /* should be zero ended, but we are paranoid. */ > s->buffer[s->seq.len] = 0; > > printk(KERN_TRACE "%s", s->buffer); > > trace_seq_init(s); > } > > I found it when checking the applied patches in origin/rfc/seq-buf > branch. I hope that it was the correct place.
Yes, that's the working branch for this code.
Anyway, I saw this and thought about using trace_seq_used(), but then I realized that this is trace_seq code which has a hard coded buffer length of PAGE_SIZE which on all archs is more than 1000 (TRACE_MAX_PRINT).
Regardless of overflow or not (or even if trace_seq is full), that if statement will prevent this from doing any buffer overflows.
s->seq.len will never be more than s->seq.size after the test against TRACE_MAX_PRINT. So I see no harm here.
trace_printk_seq() is for dumping the ring buffer to console, which is usually something done on panic. It's special.
-- Steve
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