Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH printk v2 7/7] printk: Handle dropped message smarter | Date | Thu, 24 Nov 2022 00:20:00 +0106 |
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From: Thomas Gleixner <tglx@linutronix.de>
If a 'dropped message' is to be printed, move the record text to be directly appended to the 'dropped message' and let console->write() output it in one go.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> --- kernel/printk/printk.c | 125 +++++++++++++++++++++++++++-------------- 1 file changed, 82 insertions(+), 43 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index dd1d8599ce5a..c4b148a7d114 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2007,31 +2007,6 @@ static int console_trylock_spinning(void) return 1; } -#if DROPPED_TEXT_MAX > CONSOLE_EXT_LOG_MAX -#error "DROPPED_TEXT_MAX too large for console_buffers->ext_text" -#endif - -/* - * 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 @@ -2412,10 +2387,6 @@ 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(int cookie) { 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; } @@ -2741,6 +2712,60 @@ static void __console_unlock(void) up_console_sem(); } +/* + * A maximum dropped message together with a maximum regular message + * must be able to fit within console_buffers->ext_text. + */ +#if DROPPED_TEXT_MAX > (CONSOLE_EXT_LOG_MAX - CONSOLE_LOG_MAX) +#error "DROPPED_TEXT_MAX too large for console_buffers->ext_text" +#endif + +/** + * msg_print_dropped - Prepend a "dropped message" if required + * @desc: Pointer to the output descriptor + * @dropped: The number of dropped messages to report + * + * Inserts the "dropped message" into the output buffer if @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 + * string-print the dropped message there and move the record text to be + * appended to the dropped message. The extended message buffer is much + * larger and can accommodate both messages. + * + * In case a dropped message is needed, this returns with @desc->outbuf + * and @desc->len updated. The caller is responsible for tracking and + * resetting the dropped count. If no dropped message is required then + * @desc is not modified. + */ +static void msg_print_dropped(struct console_message *cmsg, unsigned long dropped) +{ + struct console_buffers *cbufs = cmsg->cbufs; + char *ext_text = &cbufs->ext_text[0]; + size_t len; + + if (!dropped || cmsg->is_extmsg) + return; + + if (WARN_ON_ONCE(cmsg->outbuf != &cbufs->text[0])) + return; + + /* Print it into ext_text, which is unused. */ + len = snprintf(ext_text, DROPPED_TEXT_MAX, + "** %lu printk messages dropped **\n", dropped); + + /* + * Append the record text to the dropped message so that it + * goes out with one write. + */ + memcpy(ext_text + len, &cbufs->text[0], cmsg->outbuf_len); + + /* Update the output buffer descriptor. */ + cmsg->outbuf = ext_text; + cmsg->outbuf_len += len; +} + /** * console_get_next_message - Fill the output buffer with the next record * @con: The console to print on @@ -2796,13 +2821,32 @@ static bool console_get_next_message(struct console *con, struct console_message len = info_print_ext_header(write_text, write_text_size, r.info); len += msg_print_ext_body(write_text + len, write_text_size - len, &r.text_buf[0], r.info->text_len, &r.info->dev_info); + + cmsg->outbuf = write_text; + cmsg->outbuf_len = len; + + /* + * Extended consoles do not print "dropped messages" + * as that can be seen from the sequence number. + */ } else { - write_text = &cbufs->text[0]; len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time); + + cmsg->outbuf = &cbufs->text[0]; + cmsg->outbuf_len = len; + + if (con->dropped) { + /* + * It is expected that @outbuf and @outbuf_len are + * already set. They will be updated after inserting + * the "dropped message". + */ + msg_print_dropped(cmsg, con->dropped); + + con->dropped = 0; + } } - cmsg->outbuf = write_text; - cmsg->outbuf_len = len; return true; } @@ -2831,7 +2875,6 @@ static bool console_emit_next_record(struct console *con, struct console_buffers .is_extmsg = console_srcu_read_flags(con) & CON_EXTENDED, }; unsigned long flags; - char *dropped_text; *handover = false; @@ -2844,14 +2887,6 @@ static bool console_emit_next_record(struct console *con, struct console_buffers goto skip; } - if (cmsg.is_extmsg) { - /* Extended consoles do not print "dropped messages". */ - dropped_text = NULL; - } else { - /* @ext_text is unused. Use it for "dropped messages". */ - dropped_text = &cbufs->ext_text[0]; - } - /* * While actively printing out messages, if another printk() * were to occur on another CPU, it may wait for this one to @@ -2865,8 +2900,12 @@ static bool console_emit_next_record(struct console *con, struct console_buffers printk_safe_enter_irqsave(flags); console_lock_spinning_enable(); - stop_critical_timings(); /* don't trace print latency */ - call_console_driver(con, cmsg.outbuf, cmsg.outbuf_len, dropped_text); + /* Do not trace print latency. */ + stop_critical_timings(); + + /* Write everything out to the hardware. */ + con->write(con, cmsg.outbuf, cmsg.outbuf_len); + start_critical_timings(); con->seq++; -- 2.30.2
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