From 22c2c7b2ef7864389b1b75f9fd604da14b21e2c2 Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Mon, 12 Dec 2016 16:45:44 -0800 Subject: [PATCH] printk/NMI: handle continuous lines and missing newline Commit 4bcc595ccd80 ("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. 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 prints the final newline as a continuous line. Finally, it moves handling of the s->len overflow into the paranoid check. And allows to recover from the disaster. Link: http://lkml.kernel.org/r/1478695291-12169-2-git-send-email-pmladek@suse.com Signed-off-by: Petr Mladek Reviewed-by: Sergey Senozhatsky Cc: Joe Perches Cc: Steven Rostedt Cc: Jason Wessel Cc: Jaroslav Kysela Cc: Takashi Iwai Cc: Chris Mason Cc: Josef Bacik Cc: David Sterba Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/printk/nmi.c | 78 +++++++++++++++++++++++++++++---------------- 1 file changed, 50 insertions(+), 28 deletions(-) diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c index 152533edc56f..f011aaef583c 100644 --- a/kernel/printk/nmi.c +++ b/kernel/printk/nmi.c @@ -114,16 +114,51 @@ 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(const char *start, size_t len) { - const char *buf = s->buffer + start; + const 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; + } + + /* Handle continuous lines or missing new line. */ + if ((c + 1 < end) && printk_get_level(c)) { + if (header) { + c = printk_skip_level(c); + continue; + } + + printk_nmi_flush_line(start, c - start); + start = c++; + header = true; + continue; + } + + header = false; + c++; + } - printk_nmi_flush_line(buf, (end - start) + 1); + /* Check if there was a partial line. Ignore pure header. */ + if (start < end && !header) { + static const char newline[] = KERN_CONT "\n"; + + printk_nmi_flush_line(start, end - start); + printk_nmi_flush_line(newline, strlen(newline)); + } + + return len; } /* @@ -136,8 +171,8 @@ 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 @@ -155,12 +190,14 @@ more: /* * 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) @@ -168,22 +205,7 @@ more: /* Make sure that 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 -- 2.30.2