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: Thu, 6 Nov 2014 17:13:13 +0100 [thread overview]
Message-ID: <20141106161313.GI2001@dhcp128.suse.cz> (raw)
In-Reply-To: <20141105134147.226a23ef@gandalf.local.home>
On Wed 2014-11-05 13:41:47, Steven Rostedt wrote:
> On Wed, 5 Nov 2014 15:22:22 +0100
> Petr Mladek <pmladek@suse.cz> wrote:
>
> > On Tue 2014-11-04 10:52:40, Steven Rostedt wrote:
> > > From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
> > Also I would add an explanation of the overall logic. If I get it
> > correctly from the code, it is:
> >
> > /*
> > * The last byte of the buffer is used to detect an overflow in some
> > * operations. Therefore, the buffer offers (@size - 1) bytes for valid
> > * data.
>
> Well, this will change in the future. And it is commented with the
> seq_buf_has_overflowed() function. I don't want to comment about it
> with the structure.
Fair enough.
> > > + */
> > > +#include <linux/uaccess.h>
> > > +#include <linux/seq_file.h>
> > > +#include <linux/seq_buf.h>
> > > +
> > > +/* How much buffer is left on the seq_buf? */
> >
> > I would write the following to explain the -1:
>
> Later patches gets rid of the -1. It's -1 because seq_file is -1 as
> well.
Yup. Let's leave it as is.
> >
> > /* How much buffer is left for valid data */
> >
> > > +#define SEQ_BUF_LEFT(s) (((s)->size - 1) - (s)->len)
> >
> > Hmm, it might overflow when the buffer has overflown (s->len == s->size)
> > or when the buffer is not initialized (s->size == 0). Note that the
> > result should be unsigned int.
>
> The two places that use it is "unsigned int" so that should not be a
> problem.
It might overflow. If ("size == len"), the result will be -1
which is UINT_MAX.
Well, this should not happen if callers check the overflow before
any use. Also we are going to remove the -1 in the followup patches.
I am fine with it after all.
> > > +
> > > +/**
> > > + * seq_buf_puts - sequence printing of simple string
> > > + * @s: seq_buf descriptor
> > > + * @str: simple string to record
> > > + *
> > > + * Copy a simple string into the sequence buffer.
> > > + *
> > > + * Returns zero on success, -1 on overflow
> > > + */
> > > +int seq_buf_puts(struct seq_buf *s, const char *str)
> > > +{
> > > + unsigned int len = strlen(str);
> > > +
> > > + WARN_ON(s->size == 0);
> > > +
> > > + if (s->len + len < s->size) {
> > > + memcpy(s->buffer + s->len, str, len);
> > > + s->len += len;
> > > + return 0;
> > > + }
> >
> > We might want to copy the maximum possible number of bytes.
> > It will then behave the same as the other functions.
>
> I'm converting all this to be like seq_file in the other patches.
Fair enough.
>
> >
> > > + *
> > > + * Returns -EFAULT if the copy to userspace fails.
> > > + */
> > > +int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
> > > +{
> > > + int len;
> > > + int ret;
> > > +
> > > + if (!cnt)
> > > + return 0;
> > > +
> > > + if (s->len <= s->readpos)
> > > + return -EBUSY;
> > > +
> > > + len = s->len - s->readpos;
> > > + if (cnt > len)
> > > + cnt = len;
> > > + ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);
> > > + if (ret == cnt)
> > > + return -EFAULT;
> > > +
> > > + cnt -= ret;
> > > +
> > > + s->readpos += cnt;
> > > + return cnt;
> > > +}
> >
> > [...]
> >
> > > diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
> > > index 1f24ed99dca2..960ccfb2f50c 100644
> > > --- a/kernel/trace/trace_seq.c
> > > +++ b/kernel/trace/trace_seq.c
> > > @@ -27,10 +27,19 @@
> > > #include <linux/trace_seq.h>
> > >
> > > /* How much buffer is left on the trace_seq? */
> > > -#define TRACE_SEQ_BUF_LEFT(s) ((PAGE_SIZE - 1) - (s)->len)
> > > +#define TRACE_SEQ_BUF_LEFT(s) ((PAGE_SIZE - 1) - (s)->seq.len)
> >
> > This might overflow when s->len == PAGE_SIZE. I think that it
> > newer happenes because we always check s->full before. The question
> > is if we really want to depend on this.
>
> Yeah, we should make this check seq_buf itself. Maybe make a static
> inline function that is in seq_buf.h.
The inline function in seq_buf.h looks like a good idea.
> >
> > > /* How much buffer is written? */
> > > -#define TRACE_SEQ_BUF_USED(s) min((s)->len, (unsigned int)(PAGE_SIZE - 1))
> > > +#define TRACE_SEQ_BUF_USED(s) min((s)->seq.len, (unsigned int)(PAGE_SIZE - 1))
> > > +
> > > +/*
> > > + * trace_seq should work with being initialized with 0s.
> > > + */
> > > +static inline void __trace_seq_init(struct trace_seq *s)
> > > +{
> > > + if (unlikely(!s->seq.size))
> > > + trace_seq_init(s);
> > > +}
> > >
> > > /**
> > > * trace_print_seq - move the contents of trace_seq into a seq_file
> > > @@ -43,10 +52,11 @@
> > > */
> > > int trace_print_seq(struct seq_file *m, struct trace_seq *s)
> > > {
> > > - unsigned int len = TRACE_SEQ_BUF_USED(s);
> > > int ret;
> > >
> > > - ret = seq_write(m, s->buffer, len);
> > > + __trace_seq_init(s);
> > > +
> > > + ret = seq_buf_print_seq(m, &s->seq);
> > >
> > > /*
> > > * Only reset this buffer if we successfully wrote to the
> > > @@ -77,25 +87,25 @@ int trace_print_seq(struct seq_file *m, struct trace_seq *s)
> > > */
> > > int trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
> > > {
> > > - unsigned int len = TRACE_SEQ_BUF_LEFT(s);
> > > + unsigned int save_len = s->seq.len;
> > > va_list ap;
> > > - int ret;
> > >
> > > - if (s->full || !len)
> > > + if (s->full)
> > > return 0;
> > >
> > > + __trace_seq_init(s);
> > > +
> > > va_start(ap, fmt);
> > > - ret = vsnprintf(s->buffer + s->len, len, fmt, ap);
> > > + seq_buf_vprintf(&s->seq, fmt, ap);
> > > va_end(ap);
> > >
> > > /* If we can't write it all, don't bother writing anything */
> > > - if (ret >= len) {
> > > + if (unlikely(seq_buf_has_overflowed(&s->seq))) {
> >
> > We might check the return value from seq_buf_vprintf() here.
>
> No, we are working to get rid of the return values for the seq_*()
> functions (with a few exceptions). One now must check if the buffer has
> overflowed, and not the return value of the seq_*() functions
> themselves.
I see.
> There's already patches out to convert the seq_file calls as well.
Good to know.
Best Regards,
Petr
next prev parent reply other threads:[~2014-11-06 16:13 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
2014-11-06 16:13 ` Petr Mladek [this message]
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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