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[PATCH] printk/nmi: avoid direct printk()-s from __printk_nmi_flush()

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From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>

__printk_nmi_flush() can be called from nmi_panic(), therefore it has to
test whether it's executed in NMI context and thus must route the messages
through deferred printk() or via direct printk(). Except for two places
where __printk_nmi_flush() does unconditional direct printk() calls:
 - pr_err("printk_nmi_flush: internal error ...")
 - pr_cont("\n")

Factor out __print_nmi_seq_line(), which takes care of in_nmi(), and use
it in __printk_nmi_flush() for printing and error-reporting.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 kernel/printk/nmi.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c
index b69eb8a..5f2c198 100644
--- a/kernel/printk/nmi.c
+++ b/kernel/printk/nmi.c
@@ -103,23 +103,32 @@ again:
  * printk one line from the temporary buffer from @start index until
  * and including the @end index.
  */
-static void print_nmi_seq_line(struct nmi_seq_buf *s, int start, int end)
+static void __print_nmi_seq_line(const char *text, int len)
 {
-	const char *buf = s->buffer + start;
-
 	/*
 	 * The buffers are flushed in NMI only on panic.  The messages must
 	 * go only into the ring buffer at this stage.  Consoles will get
 	 * explicitly called later when a crashdump is not generated.
 	 */
 	if (in_nmi())
-		printk_deferred("%.*s", (end - start) + 1, buf);
+		printk_deferred("%.*s", len, text);
 	else
-		printk("%.*s", (end - start) + 1, buf);
+		printk("%.*s", len, text);
 
 }
 
 /*
+ * printk one line from the temporary buffer from @start index until
+ * and including the @end index.
+ */
+static void print_nmi_seq_line(struct nmi_seq_buf *s, int start, int end)
+{
+	const char *buf = s->buffer + start;
+
+	__print_nmi_seq_line(buf, (end - start) + 1);
+}
+
+/*
  * Flush data from the associated per_CPU buffer. The function
  * can be called either via IRQ work or independently.
  */
@@ -150,9 +159,11 @@ more:
 	 * the buffer an unexpected way. If we printed something then
 	 * @len must only increase.
 	 */
-	if (i && i >= len)
-		pr_err("printk_nmi_flush: internal error: i=%d >= len=%zu\n",
-		       i, len);
+	if (i && i >= len) {
+		const char *msg = "printk_nmi_flush: internal error\n";
+
+		__print_nmi_seq_line(msg, strlen(msg));
+	}
 
 	if (!len)
 		goto out; /* Someone else has already flushed the buffer. */
@@ -173,7 +184,7 @@ more:
 	/* Check if there was a partial line. */
 	if (last_i < size) {
 		print_nmi_seq_line(s, last_i, size - 1);
-		pr_cont("\n");
+		__print_nmi_seq_line("\n", strlen("\n"));
 	}
 
 	/*
-- 
2.9.3

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[PATCH] printk/nmi: avoid direct printk()-s from __printk_nmi_flush() Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-08-29 14:40 +0200
  Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Petr Mladek <pmladek@suse.com> - 2016-08-29 17:20 +0200
    Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-08-30 03:10 +0200
    Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-08-30 10:00 +0200
      Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Petr Mladek <pmladek@suse.com> - 2016-08-30 11:10 +0200
        Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-08-30 11:40 +0200
          Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Petr Mladek <pmladek@suse.com> - 2016-08-30 13:20 +0200
            Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-08-31 06:10 +0200
            Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-09-01 10:00 +0200
              Re: [PATCH] printk/nmi: avoid direct printk()-s from  __printk_nmi_flush() Petr Mladek <pmladek@suse.com> - 2016-09-01 10:20 +0200

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