From: Petr Mladek <pmladek@suse.cz>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jiri Kosina <jkosina@suse.cz>, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC][PATCH 03/12 v3] tracing: Create seq_buf layer in trace_seq
Date: Mon, 10 Nov 2014 20:02:49 +0100 [thread overview]
Message-ID: <20141110190249.GD2552@dhcp128.suse.cz> (raw)
In-Reply-To: <20141110123747.6ef3dd07@gandalf.local.home>
On Mon 2014-11-10 12:37:47, Steven Rostedt wrote:
> On Mon, 10 Nov 2014 14:53:30 +0100
> Petr Mladek <pmladek@suse.cz> wrote:
>
> > > +/*
> > > + * How much buffer is left on the seq_buf?
> > > + */
> > > +static inline unsigned int
> > > +seq_buf_buffer_left(struct seq_buf *s)
> > > +{
> > > + return (s->size - 1) - s->len;
> >
> > This should be
> >
> > if (seq_buf_has_overflowed(s)
> > return 0;
> > return (s->size - 1) - s->len;
> >
> > otherwise, it would return UNIT_MAX for the overflown state. If I am
> > not mistaken.
>
> I guess I could add that. Probably the safer bet. Or document it that
> this is undefined if buffer has overflowed. I have to check how my use
> cases worked.
>
> Probably best to add the overflow check anyway.
I vote for it :-)
> > [...]
> >
> > > diff --git a/kernel/trace/seq_buf.c b/kernel/trace/seq_buf.c
> > > new file mode 100644
> > > index 000000000000..88738b200bf3
> > > --- /dev/null
> > > +++ b/kernel/trace/seq_buf.c
> >
> > [...]
> >
> > > +
> > > +/**
> > > + * seq_buf_bitmask - write a bitmask array in its ASCII representation
> > > + * @s: seq_buf descriptor
> > > + * @maskp: points to an array of unsigned longs that represent a bitmask
> > > + * @nmaskbits: The number of bits that are valid in @maskp
> > > + *
> > > + * Writes a ASCII representation of a bitmask string into @s.
> > > + *
> > > + * Returns zero on success, -1 on overflow.
> > > + */
> > > +int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
> > > + int nmaskbits)
> > > +{
> > > + unsigned int len = seq_buf_buffer_left(s);
> > > + int ret;
> > > +
> > > + WARN_ON(s->size == 0);
> > > +
> > > + /*
> > > + * The last byte of the buffer is used to determine if we
> > > + * overflowed or not.
> > > + */
> > > + if (len > 1) {
> > > + ret = bitmap_scnprintf(s->buffer, len, maskp, nmaskbits);
> >
> > It should be:
> >
> > ret = bitmap_scnprintf(s->buffer + s->len, len,
> > maskp, nmaskbits);
> >
> > otherwise, we would write to the beginning to the buffer.
>
> You are correct. But I'll make that a separate patch. This is just
> keeping the bug that was in the original code.
Fair enough.
> >
> > > + if (ret < len) {
> > > + s->len += ret;
> > > + return 0;
> > > + }
> > > + }
> > > + seq_buf_set_overflow(s);
> > > + return -1;
> > > +}
> > > +
> >
> > [...]
> >
> > > diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
> > > index 1f24ed99dca2..3ad8738aea19 100644
> > > --- a/kernel/trace/trace_seq.c
> > > +++ b/kernel/trace/trace_seq.c
> >
> > [...]
> >
> > > @@ -144,23 +160,24 @@ EXPORT_SYMBOL_GPL(trace_seq_bitmask);
> > > */
> > > int trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args)
> > > {
> > > - unsigned int len = TRACE_SEQ_BUF_LEFT(s);
> > > + unsigned int save_len = s->seq.len;
> > > int ret;
> > >
> > > - if (s->full || !len)
> > > + if (s->full)
> > > return 0;
> > >
> > > - ret = vsnprintf(s->buffer + s->len, len, fmt, args);
> > > + __trace_seq_init(s);
> > > +
> > > + ret = seq_buf_vprintf(&s->seq, fmt, args);
> >
> > Note that this returns 0 on success => we do not need to store it
> >
> > > /* If we can't write it all, don't bother writing anything */
> > > - if (ret >= len) {
> > > + if (unlikely(seq_buf_has_overflowed(&s->seq))) {
> > > + s->seq.len = save_len;
> > > s->full = 1;
> > > return 0;
> > > }
> > >
> > > - s->len += ret;
> > > -
> > > - return len;
> > > + return ret;
> >
> > Instead, we have to do something like:
> >
> > return s->seq.len - save_len;
>
> Actually, I need to make the trace_seq_*() functions return the same as
> the seq_buf_*() functions.
>
> I'll update this for now, but it's gotta change later. Probably why I
> wasn't so careful about it.
>
> Hmm, I may make the trace_seq_*() functions not return length written
> first, before pulling out the seq_buf_*() code. That is, make the
> trace_seq_*() behave more like what the seq_buf_*() code does first,
> before pulling out the seq_buf_*() code.
Sounds like the best solution if it does not cause too many changes in
the trace_seq() callers.
Best Regards,
Petr
next prev parent reply other threads:[~2014-11-10 19:02 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-04 15:52 [RFC][PATCH 00/12 v3] seq-buf/x86/printk: Print all stacks from NMI safely Steven Rostedt
2014-11-04 15:52 ` [RFC][PATCH 01/12 v3] x86/kvm/tracing: Use helper function trace_seq_buffer_ptr() Steven Rostedt
2014-11-04 16:27 ` Paolo Bonzini
2014-11-04 17:17 ` Rustad, Mark D
2014-11-04 19:09 ` Steven Rostedt
2014-11-04 19:35 ` Steven Rostedt
2014-11-04 20:09 ` Rustad, Mark D
2014-11-05 10:28 ` Petr Mladek
2014-11-04 15:52 ` [RFC][PATCH 02/12 v3] RAS/tracing: Use trace_seq_buffer_ptr() helper instead of open coded Steven Rostedt
2014-11-04 19:59 ` Borislav Petkov
2014-11-05 10:29 ` Petr Mladek
2014-11-04 15:52 ` [RFC][PATCH 03/12 v3] tracing: Create seq_buf layer in trace_seq Steven Rostedt
2014-11-05 14:22 ` Petr Mladek
2014-11-05 18:41 ` Steven Rostedt
2014-11-05 20:00 ` Steven Rostedt
2014-11-05 21:17 ` Steven Rostedt
2014-11-05 21:21 ` Steven Rostedt
2014-11-06 16:33 ` Petr Mladek
2014-11-07 18:30 ` Steven Rostedt
2014-11-07 18:59 ` Joe Perches
2014-11-07 19:10 ` Steven Rostedt
2014-11-10 13:53 ` Petr Mladek
2014-11-10 17:37 ` Steven Rostedt
2014-11-10 19:02 ` Petr Mladek [this message]
2014-11-06 16:13 ` Petr Mladek
2014-11-05 14:26 ` Petr Mladek
2014-11-05 18:42 ` Steven Rostedt
2014-11-04 15:52 ` [RFC][PATCH 04/12 v3] tracing: Convert seq_buf_path() to be like seq_path() Steven Rostedt
2014-11-05 14:45 ` Petr Mladek
2014-11-05 20:10 ` Steven Rostedt
2014-11-06 14:18 ` Petr Mladek
2014-11-06 21:09 ` Steven Rostedt
2014-11-06 15:01 ` Petr Mladek
2014-11-07 18:34 ` Steven Rostedt
2014-11-10 14:03 ` Petr Mladek
2014-11-10 17:38 ` Steven Rostedt
2014-11-04 15:52 ` [RFC][PATCH 05/12 v3] tracing: Convert seq_buf fields to be like seq_file fields Steven Rostedt
2014-11-05 15:57 ` Petr Mladek
2014-11-05 20:14 ` Steven Rostedt
2014-11-06 14:24 ` Petr Mladek
2014-11-04 15:52 ` [RFC][PATCH 06/12 v3] tracing: Add a seq_buf_clear() helper and clear len and readpos in init Steven Rostedt
2014-11-05 16:00 ` Petr Mladek
2014-11-04 15:52 ` [RFC][PATCH 07/12 v3] tracing: Have seq_buf use full buffer Steven Rostedt
2014-11-05 16:31 ` Petr Mladek
2014-11-05 20:21 ` Steven Rostedt
2014-11-05 21:06 ` Steven Rostedt
2014-11-06 15:31 ` Petr Mladek
2014-11-06 19:24 ` Steven Rostedt
2014-11-07 9:11 ` Petr Mladek
2014-11-07 18:37 ` Steven Rostedt
2014-11-10 18:11 ` Petr Mladek
2014-11-06 15:13 ` Petr Mladek
2014-11-04 15:52 ` [RFC][PATCH 08/12 v3] tracing: Add seq_buf_get_buf() and seq_buf_commit() helper functions Steven Rostedt
2014-11-05 16:51 ` Petr Mladek
2014-11-05 20:26 ` Steven Rostedt
2014-11-07 18:39 ` Steven Rostedt
2014-11-10 18:33 ` Petr Mladek
2014-11-10 19:23 ` Steven Rostedt
2014-11-04 15:52 ` [RFC][PATCH 09/12 v3] seq_buf: Move the seq_buf code to lib/ Steven Rostedt
2014-11-05 16:57 ` Petr Mladek
2014-11-05 20:32 ` Steven Rostedt
2014-11-04 15:52 ` [RFC][PATCH 10/12 v3] seq-buf: Make seq_buf_bprintf() conditional on CONFIG_BINARY_PRINTF Steven Rostedt
2014-11-05 17:06 ` Petr Mladek
2014-11-05 20:33 ` Steven Rostedt
2014-11-05 20:42 ` Steven Rostedt
2014-11-06 14:39 ` Petr Mladek
2014-11-07 20:36 ` Junio C Hamano
2014-11-07 21:49 ` Steven Rostedt
2014-11-10 18:43 ` Petr Mladek
2014-11-04 15:52 ` [RFC][PATCH 11/12 v3] printk: Add per_cpu printk func to allow printk to be diverted Steven Rostedt
2014-11-06 16:56 ` Petr Mladek
2014-11-04 15:52 ` [RFC][PATCH 12/12 v3] x86/nmi: Perform a safe NMI stack trace on all CPUs Steven Rostedt
2014-11-04 23:05 ` Jiri Kosina
2014-11-04 23:41 ` Steven Rostedt
2014-11-06 18:41 ` Petr Mladek
2014-11-07 18:56 ` Steven Rostedt
2014-11-10 18:58 ` Petr Mladek
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