diff options
Diffstat (limited to 'debian/patches-rt/0081-printk-remove-logbuf_lock-writer-protection-of-ringb.patch')
| -rw-r--r-- | debian/patches-rt/0081-printk-remove-logbuf_lock-writer-protection-of-ringb.patch | 251 |
1 files changed, 251 insertions, 0 deletions
diff --git a/debian/patches-rt/0081-printk-remove-logbuf_lock-writer-protection-of-ringb.patch b/debian/patches-rt/0081-printk-remove-logbuf_lock-writer-protection-of-ringb.patch new file mode 100644 index 000000000..15ea7d1b6 --- /dev/null +++ b/debian/patches-rt/0081-printk-remove-logbuf_lock-writer-protection-of-ringb.patch @@ -0,0 +1,251 @@ +From c2d6c379547a29aa25202641659917ecd9ae7712 Mon Sep 17 00:00:00 2001 +From: John Ogness <john.ogness@linutronix.de> +Date: Wed, 9 Dec 2020 01:50:53 +0106 +Subject: [PATCH 081/323] printk: remove logbuf_lock writer-protection of + ringbuffer +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz + +Since the ringbuffer is lockless, there is no need for it to be +protected by @logbuf_lock. Remove @logbuf_lock writer-protection of +the ringbuffer. The reader-protection is not removed because some +variables, used by readers, are using @logbuf_lock for synchronization: +@syslog_seq, @syslog_time, @syslog_partial, @console_seq, +struct kmsg_dumper. + +For PRINTK_NMI_DIRECT_CONTEXT_MASK, @logbuf_lock usage is not removed +because it may be used for dumper synchronization. + +Without @logbuf_lock synchronization of vprintk_store() it is no +longer possible to use the single static buffer for temporarily +sprint'ing the message. Instead, use vsnprintf() to determine the +length and perform the real vscnprintf() using the area reserved from +the ringbuffer. This leads to suboptimal packing of the message data, +but will result in less wasted storage than multiple per-cpu buffers +to support lockless temporary sprint'ing. + +Signed-off-by: John Ogness <john.ogness@linutronix.de> +Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> +Reviewed-by: Petr Mladek <pmladek@suse.com> +Signed-off-by: Petr Mladek <pmladek@suse.com> +Link: https://lore.kernel.org/r/20201209004453.17720-3-john.ogness@linutronix.de +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/printk/printk.c | 138 +++++++++++++++++++++++++++++------------ + 1 file changed, 98 insertions(+), 40 deletions(-) + +diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c +index 9a7c2b561e6d..b0a3f7827819 100644 +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -1129,7 +1129,7 @@ void __init setup_log_buf(int early) + new_descs, ilog2(new_descs_count), + new_infos); + +- logbuf_lock_irqsave(flags); ++ printk_safe_enter_irqsave(flags); + + log_buf_len = new_log_buf_len; + log_buf = new_log_buf; +@@ -1146,7 +1146,7 @@ void __init setup_log_buf(int early) + */ + prb = &printk_rb_dynamic; + +- logbuf_unlock_irqrestore(flags); ++ printk_safe_exit_irqrestore(flags); + + if (seq != prb_next_seq(&printk_rb_static)) { + pr_err("dropped %llu messages\n", +@@ -1887,18 +1887,90 @@ static inline u32 printk_caller_id(void) + 0x80000000 + raw_smp_processor_id(); + } + +-/* Must be called under logbuf_lock. */ ++/** ++ * parse_prefix - Parse level and control flags. ++ * ++ * @text: The terminated text message. ++ * @level: A pointer to the current level value, will be updated. ++ * @lflags: A pointer to the current log flags, will be updated. ++ * ++ * @level may be NULL if the caller is not interested in the parsed value. ++ * Otherwise the variable pointed to by @level must be set to ++ * LOGLEVEL_DEFAULT in order to be updated with the parsed value. ++ * ++ * @lflags may be NULL if the caller is not interested in the parsed value. ++ * Otherwise the variable pointed to by @lflags will be OR'd with the parsed ++ * value. ++ * ++ * Return: The length of the parsed level and control flags. ++ */ ++static u16 parse_prefix(char *text, int *level, enum log_flags *lflags) ++{ ++ u16 prefix_len = 0; ++ int kern_level; ++ ++ while (*text) { ++ kern_level = printk_get_level(text); ++ if (!kern_level) ++ break; ++ ++ switch (kern_level) { ++ case '0' ... '7': ++ if (level && *level == LOGLEVEL_DEFAULT) ++ *level = kern_level - '0'; ++ break; ++ case 'c': /* KERN_CONT */ ++ if (lflags) ++ *lflags |= LOG_CONT; ++ } ++ ++ prefix_len += 2; ++ text += 2; ++ } ++ ++ return prefix_len; ++} ++ ++static u16 printk_sprint(char *text, u16 size, int facility, enum log_flags *lflags, ++ const char *fmt, va_list args) ++{ ++ u16 text_len; ++ ++ text_len = vscnprintf(text, size, fmt, args); ++ ++ /* Mark and strip a trailing newline. */ ++ if (text_len && text[text_len - 1] == '\n') { ++ text_len--; ++ *lflags |= LOG_NEWLINE; ++ } ++ ++ /* Strip log level and control flags. */ ++ if (facility == 0) { ++ u16 prefix_len; ++ ++ prefix_len = parse_prefix(text, NULL, NULL); ++ if (prefix_len) { ++ text_len -= prefix_len; ++ memmove(text, text + prefix_len, text_len); ++ } ++ } ++ ++ return text_len; ++} ++ ++__printf(4, 0) + int vprintk_store(int facility, int level, + const struct dev_printk_info *dev_info, + const char *fmt, va_list args) + { + const u32 caller_id = printk_caller_id(); +- static char textbuf[LOG_LINE_MAX]; + struct prb_reserved_entry e; + enum log_flags lflags = 0; + struct printk_record r; + u16 trunc_msg_len = 0; +- char *text = textbuf; ++ char prefix_buf[8]; ++ u16 reserve_size; ++ va_list args2; + u16 text_len; + u64 ts_nsec; + +@@ -1911,35 +1983,21 @@ int vprintk_store(int facility, int level, + ts_nsec = local_clock(); + + /* +- * The printf needs to come first; we need the syslog +- * prefix which might be passed-in as a parameter. ++ * The sprintf needs to come first since the syslog prefix might be ++ * passed in as a parameter. An extra byte must be reserved so that ++ * later the vscnprintf() into the reserved buffer has room for the ++ * terminating '\0', which is not counted by vsnprintf(). + */ +- text_len = vscnprintf(text, sizeof(textbuf), fmt, args); +- +- /* mark and strip a trailing newline */ +- if (text_len && text[text_len-1] == '\n') { +- text_len--; +- lflags |= LOG_NEWLINE; +- } +- +- /* strip kernel syslog prefix and extract log level or control flags */ +- if (facility == 0) { +- int kern_level; ++ va_copy(args2, args); ++ reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1; ++ va_end(args2); + +- while ((kern_level = printk_get_level(text)) != 0) { +- switch (kern_level) { +- case '0' ... '7': +- if (level == LOGLEVEL_DEFAULT) +- level = kern_level - '0'; +- break; +- case 'c': /* KERN_CONT */ +- lflags |= LOG_CONT; +- } ++ if (reserve_size > LOG_LINE_MAX) ++ reserve_size = LOG_LINE_MAX; + +- text_len -= 2; +- text += 2; +- } +- } ++ /* Extract log level or control flags. */ ++ if (facility == 0) ++ parse_prefix(&prefix_buf[0], &level, &lflags); + + if (level == LOGLEVEL_DEFAULT) + level = default_message_loglevel; +@@ -1948,9 +2006,10 @@ int vprintk_store(int facility, int level, + lflags |= LOG_NEWLINE; + + if (lflags & LOG_CONT) { +- prb_rec_init_wr(&r, text_len); ++ prb_rec_init_wr(&r, reserve_size); + if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) { +- memcpy(&r.text_buf[r.info->text_len], text, text_len); ++ text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size, ++ facility, &lflags, fmt, args); + r.info->text_len += text_len; + + if (lflags & LOG_NEWLINE) { +@@ -1969,18 +2028,18 @@ int vprintk_store(int facility, int level, + * prb_reserve_in_last() and prb_reserve() purposely invalidate the + * structure when they fail. + */ +- prb_rec_init_wr(&r, text_len); ++ prb_rec_init_wr(&r, reserve_size); + if (!prb_reserve(&e, prb, &r)) { + /* truncate the message if it is too long for empty buffer */ +- truncate_msg(&text_len, &trunc_msg_len); ++ truncate_msg(&reserve_size, &trunc_msg_len); + +- prb_rec_init_wr(&r, text_len + trunc_msg_len); ++ prb_rec_init_wr(&r, reserve_size + trunc_msg_len); + if (!prb_reserve(&e, prb, &r)) + return 0; + } + + /* fill message */ +- memcpy(&r.text_buf[0], text, text_len); ++ text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &lflags, fmt, args); + if (trunc_msg_len) + memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len); + r.info->text_len = text_len + trunc_msg_len; +@@ -2021,10 +2080,9 @@ asmlinkage int vprintk_emit(int facility, int level, + boot_delay_msec(level); + printk_delay(); + +- /* This stops the holder of console_sem just where we want him */ +- logbuf_lock_irqsave(flags); ++ printk_safe_enter_irqsave(flags); + printed_len = vprintk_store(facility, level, dev_info, fmt, args); +- logbuf_unlock_irqrestore(flags); ++ printk_safe_exit_irqrestore(flags); + + /* If called from the scheduler, we can not call up(). */ + if (!in_sched) { +-- +2.43.0 + |