Messages in this thread | | | Subject | Re: [PATCH 1/4] printk/NMI: Handle continuous lines and missing newline | From | Joe Perches <> | Date | Thu, 27 Oct 2016 09:35:25 -0700 |
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On Thu, 2016-10-27 at 17:52 +0200, Petr Mladek wrote: > The commit 4bcc595ccd80decb4245 ("printk: reinstate KERN_CONT for printing > continuation lines") added back KERN_CONT message header. As a result > it might appear in the middle of the line when the parts are squashed > via the temporary NMI buffer. > > A reasonable solution seems to be to split the text in the NNI temporary > not only by newlines but also by the message headers. > > Another solution would be to filter out KERN_CONT when writing to > the temporary buffer. But this would complicate the lockless handling. > Also it would not solve problems with a missing newline that was there > even before the KERN_CONT stuff.
I believe the proper solution there is add the missing EOL/newlines where appropriate. There aren't many treewide. Maybe a couple dozen vs the 250,000 messages with newlines.
> This patch moves the temporary buffer handling into separate function. > I played with it and it seems that using the char pointers make the > code easier to read. > > Also it moves handling of the s->len overflow into the paranoid check. > And allows to recover from the disaster. > > Signed-off-by: Petr Mladek <pmladek@suse.com> > --- > kernel/printk/nmi.c | 78 +++++++++++++++++++++++++++++++++-------------------- > 1 file changed, 49 insertions(+), 29 deletions(-) > > diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c > index 16bab471c7e2..740c90efc65d 100644 > --- a/kernel/printk/nmi.c > +++ b/kernel/printk/nmi.c > @@ -113,16 +113,49 @@ static void printk_nmi_flush_line(const char *text, int len) > > } > > -/* > - * printk one line from the temporary buffer from @start index until > - * and including the @end index. > - */ > -static void printk_nmi_flush_seq_line(struct nmi_seq_buf *s, > - int start, int end) > +/* printk part of the temporary buffer line by line */ > +static int printk_nmi_flush_buffer(unsigned char *start, size_t len)
const unsigned char *?
> { > - const char *buf = s->buffer + start; > + unsigned char *c, *end; > + bool header; > + > + c = start; > + end = start + len; > + header = true; > + > + /* Print line by line. */ > + while (c < end) { > + if (*c == '\n') { > + printk_nmi_flush_line(start, c - start + 1); > + start = ++c; > + header = true; > + continue; > + } > > - printk_nmi_flush_line(buf, (end - start) + 1); > + /* Handle continuous lines or missing new line. */ > + if ((c + 1 < end) && printk_get_level(c)) { > + if (header) { > + c += 2;
printk_skip_level
> + continue; > + } > + > + printk_nmi_flush_line(start, c - start); > + start = c++; > + header = true; > + continue; > + } > + > + header = false; > + c++; > + } > + > + /* Check if there was a partial line. Ignore pure header. */ > + if (start < end && !header) { > + printk_nmi_flush_line(start, end - start); > + printk_nmi_flush_line("\n", strlen("\n")); > + } > + > + return len; > } > > /* > @@ -135,8 +168,8 @@ static void __printk_nmi_flush(struct irq_work *work) > __RAW_SPIN_LOCK_INITIALIZER(read_lock); > struct nmi_seq_buf *s = container_of(work, struct nmi_seq_buf, work); > unsigned long flags; > - size_t len, size; > - int i, last_i; > + size_t len; > + int i; > > /* > * The lock has two functions. First, one reader has to flush all > @@ -154,35 +187,22 @@ static void __printk_nmi_flush(struct irq_work *work) > /* > * This is just a paranoid check that nobody has manipulated > * the buffer an unexpected way. If we printed something then > - * @len must only increase. > + * @len must only increase. Also it should never overflow the > + * buffer size. > */ > - if (i && i >= len) { > + if ((i && i >= len) || len > sizeof(s->buffer)) { > const char *msg = "printk_nmi_flush: internal error\n"; > > printk_nmi_flush_line(msg, strlen(msg)); > + len = 0; > } > > if (!len) > goto out; /* Someone else has already flushed the buffer. */ > > - /* Make sure that data has been written up to the @len */ > + /* Make sure the data has been written up to the @len */ > smp_rmb(); > - > - size = min(len, sizeof(s->buffer)); > - last_i = i; > - > - /* Print line by line. */ > - for (; i < size; i++) { > - if (s->buffer[i] == '\n') { > - printk_nmi_flush_seq_line(s, last_i, i); > - last_i = i + 1; > - } > - } > - /* Check if there was a partial line. */ > - if (last_i < size) { > - printk_nmi_flush_seq_line(s, last_i, size - 1); > - printk_nmi_flush_line("\n", strlen("\n")); > - } > + i += printk_nmi_flush_buffer(s->buffer + i, len - i); > > /* > * Check that nothing has got added in the meantime and truncate
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