Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH printk 18/18] printk: Handle dropped message smarter | Date | Sat, 24 Sep 2022 02:10:54 +0206 |
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From: Thomas Gleixner <tglx@linutronix.de>
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@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> --- include/linux/console.h | 12 +++--- kernel/printk/printk.c | 86 +++++++++++++++++++++++++++-------------- 2 files changed, 61 insertions(+), 37 deletions(-)
diff --git a/include/linux/console.h b/include/linux/console.h index 590ab62c01d9..83563694cc82 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -176,28 +176,26 @@ 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; }; diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index c9207d81b90c..14ddd5c9363f 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1961,27 +1961,6 @@ static int console_trylock_spinning(void) return 1; } -/* - * 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 @@ -2361,10 +2340,6 @@ static ssize_t msg_print_ext_body(char *buf, size_t size, 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; } @@ -2689,6 +2664,46 @@ 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 @@ -2742,17 +2757,26 @@ static bool cons_fill_outbuf(struct console *con, struct cons_outbuf_desc *desc) } 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; } @@ -2805,8 +2829,10 @@ static bool console_emit_next_record(struct console *con, struct cons_text_buf * 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++; -- 2.30.2
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