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 <[email protected]>
> ---
> 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
