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Date: Sun, 11 Sep 2022 00:27:59 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: John Ogness <john.ogness@...utronix.de>,
Petr Mladek <pmladek@...e.com>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Linus Torvalds <torvalds@...uxfoundation.org>,
Peter Zijlstra <peterz@...radead.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Daniel Vetter <daniel@...ll.ch>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Helge Deller <deller@....de>,
Jason Wessel <jason.wessel@...driver.com>,
Daniel Thompson <daniel.thompson@...aro.org>
Subject: [patch RFC 18/29] printk: Handle dropped message smarter
No need for an extra buffer type. Regular formatting which needs the '$N
messages dropped' printout can sprintf() it into the unused extended text
buffer.
As a further simplification move the 'dropped' message right in front of
the actual record text and let the write function output it in one go.
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
include/linux/console.h | 12 ++----
kernel/printk/printk.c | 86 +++++++++++++++++++++++++++++++-----------------
2 files changed, 61 insertions(+), 37 deletions(-)
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -175,28 +175,26 @@ enum cons_flags {
/**
* struct cons_text_buf - console output text buffer
* @ext_text: Buffer for extended log format text
- * @dropped_text: Buffer for dropped text
* @text: Buffer for ringbuffer text
*/
struct cons_text_buf {
- union {
- char ext_text[CONSOLE_EXT_LOG_MAX];
- char dropped_text[DROPPED_TEXT_MAX];
- };
- char text[CONSOLE_LOG_MAX];
-};
+ char ext_text[CONSOLE_EXT_LOG_MAX];
+ char text[CONSOLE_LOG_MAX];
+} __no_randomize_layout;
/**
* struct cons_outbuf_desc - console output buffer descriptor
* @txtbuf: Pointer to buffer for storing the text
* @outbuf: Pointer to the position in @buffer for
* writing it out to the device
+ * @dropped: The dropped count
* @len: Message length
* @extmsg: Select extended format printing
*/
struct cons_outbuf_desc {
struct cons_text_buf *txtbuf;
char *outbuf;
+ unsigned long dropped;
unsigned int len;
bool extmsg;
};
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1957,27 +1957,6 @@ static int console_trylock_spinning(void
}
/*
- * Call the specified console driver, asking it to write out the specified
- * text and length. If @dropped_text is non-NULL and any records have been
- * dropped, a dropped message will be written out first.
- */
-static void call_console_driver(struct console *con, const char *text, size_t len,
- char *dropped_text)
-{
- size_t dropped_len;
-
- if (con->dropped && dropped_text) {
- dropped_len = snprintf(dropped_text, DROPPED_TEXT_MAX,
- "** %lu printk messages dropped **\n",
- con->dropped);
- con->dropped = 0;
- con->write(con, dropped_text, dropped_len);
- }
-
- con->write(con, text, len);
-}
-
-/*
* Recursion is tracked separately on each CPU. If NMIs are supported, an
* additional NMI context per CPU is also separately tracked. Until per-CPU
* is available, a separate "early tracking" is performed.
@@ -2356,10 +2335,6 @@ static ssize_t msg_print_ext_body(char *
struct dev_printk_info *dev_info) { return 0; }
static void console_lock_spinning_enable(void) { }
static int console_lock_spinning_disable_and_check(void) { return 0; }
-static void call_console_driver(struct console *con, const char *text, size_t len,
- char *dropped_text)
-{
-}
static bool suppress_message_printing(int level) { return false; }
static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
@@ -2684,6 +2659,46 @@ static void __console_unlock(void)
up_console_sem();
}
+/**
+ * cons_print_dropped - Print 'dropped' message if required
+ * @desc: Pointer to the output descriptor
+ *
+ * Prints the 'dropped' message info the output buffer if @desc->dropped is
+ * not 0 and the regular format is requested. Extended format does not
+ * need this message because it prints the sequence numbers.
+ *
+ * In regular format the extended message buffer is not in use.
+ * So print into it at the beginning and move the resulting string
+ * just in front of the regular text buffer so that the message can
+ * be printed in one go.
+ *
+ * In case of a message this returns with @desc->outbuf and @desc->len
+ * updated. If no message is required then @desc is not modified.
+ */
+static void cons_print_dropped(struct cons_outbuf_desc *desc)
+{
+ struct cons_text_buf *txtbuf = desc->txtbuf;
+ size_t len;
+
+ if (!desc->dropped || desc->extmsg)
+ return;
+
+ if (WARN_ON_ONCE(desc->outbuf != txtbuf->text))
+ return;
+
+ /* Print it into ext_text which is unused */
+ len = snprintf(txtbuf->ext_text, DROPPED_TEXT_MAX,
+ "** %lu printk messages dropped **\n", desc->dropped);
+ desc->dropped = 0;
+
+ /* Copy it just below text so it goes out with one write */
+ memcpy(txtbuf->text - len, txtbuf->ext_text, len);
+
+ /* Update the descriptor */
+ desc->len += len;
+ desc->outbuf -= len;
+}
+
/**
* cons_fill_outbuf - Fill the output buffer with the next record
@@ -2737,17 +2752,26 @@ static bool cons_fill_outbuf(struct cons
}
if (desc->extmsg) {
+ /*
+ * Extended messages do not require "dropped" message
+ * as that can be seen from the sequence number
+ */
write_text = txtbuf->ext_text;
len = info_print_ext_header(write_text, CONSOLE_EXT_LOG_MAX, r.info);
len += msg_print_ext_body(write_text + len, CONSOLE_EXT_LOG_MAX - len,
&r.text_buf[0], r.info->text_len, &r.info->dev_info);
+ desc->len = len;
+ desc->outbuf = write_text;
} else {
- write_text = txtbuf->text;
len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
+
+ desc->len = len;
+ desc->outbuf = txtbuf->text;
+ desc->dropped = con->dropped;
+ cons_print_dropped(desc);
+ con->dropped = desc->dropped;
}
- desc->len = len;
- desc->outbuf = write_text;
return true;
}
@@ -2800,8 +2824,10 @@ static bool console_emit_next_record(str
printk_safe_enter_irqsave(flags);
console_lock_spinning_enable();
- stop_critical_timings(); /* don't trace print latency */
- call_console_driver(con, desc.outbuf, desc.len, extmsg ? NULL : txtbuf->dropped_text);
+ /* don't trace print latency */
+ stop_critical_timings();
+ /* Write everything out to the hardware */
+ con->write(con, desc.outbuf, desc.len);
start_critical_timings();
con->seq++;
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