On Mon 29-09-14 13:58:57, Hannes Reinecke wrote:
> This patch splits off the actual logging from vprintk_emit()
> into printk_emit_string(), with vprintk_emit() just being a
> simple wrapper for formatting the message into a
> static buffer.
>
> With that the caller can pass in a local buffer for
> printk_emit_string() without increasing the overall stack size.
>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>
Adding Andrew into CC here as well.
There is one potential problem, see below.
> Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
> ---
> include/linux/printk.h | 5 +++++
> kernel/printk/printk.c | 36 ++++++++++++++++++++++++------------
> 2 files changed, 29 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index d78125f..9639900 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -130,6 +130,11 @@ int vprintk_emit(int facility, int level,
> const char *dict, size_t dictlen,
> const char *fmt, va_list args);
>
> +asmlinkage
> +int printk_emit_string(int facility, int level,
> + const char *dict, size_t dictlen,
> + char *textbuf, size_t text_len);
> +
> asmlinkage __printf(1, 0)
> int vprintk(const char *fmt, va_list args);
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index d13675e..303a1fe 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1618,22 +1618,11 @@ asmlinkage int vprintk_emit(int facility, int level,
> const char *dict, size_t dictlen,
> const char *fmt, va_list args)
> {
> - static int recursion_bug;
> static char textbuf[LOG_LINE_MAX];
>
> char *text = textbuf;
> size_t text_len = 0;
> - enum log_flags lflags = 0;
> - unsigned long flags;
> - int this_cpu;
> - int printed_len = 0;
> - bool in_sched = false;
> - /* cpu currently holding logbuf_lock in this function */
> - static volatile unsigned int logbuf_cpu = UINT_MAX;
>
> if (level == SCHED_MESSAGE_LOGLEVEL) {
> - level = -1;
> - in_sched = true;
> -
> /*
> * The printf needs to come first; we need the syslog
> * prefix which might be passed-in as a parameter.
> @@ -1644,6 +1633,24 @@ asmlinkage int vprintk_emit(int facility, int level,
>
> text_len += vscnprintf(text + text_len,
> sizeof(textbuf) - text_len, fmt, args);
> + return printk_emit_string(facility, level, dict, dictlen,
> + textbuf, text_len);
> +}
> +EXPORT_SYMBOL(vprintk_emit);
> +
> +asmlinkage int printk_emit_string(int facility, int level,
> + const char *dict, size_t dictlen,
> + char *textbuf, size_t text_len)
> +{
> + static int recursion_bug;
> + char *text = textbuf;
> + enum log_flags lflags = 0;
> + unsigned long flags;
> + int this_cpu;
> + int printed_len = 0;
> + bool in_sched = false;
> + /* cpu currently holding logbuf_lock in this function */
> + static volatile unsigned int logbuf_cpu = UINT_MAX;
We should make sure that text_len is lower or equal LOG_LINE_MAX.
I am afraid that printk() code is not able to process longer
lines. For example, syslog_print() does:
text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
Then it calls msg_print_text() that works with entire messages. So,
any longer message would freeze syslog_print() because it would newer
fit into the buffer.
I guess that there are more locations like this.
Maybe, we should make LOG_LINE_MAX public, so it could be used on the
other location either to allocate the buffer or to check the size.
Best Regards,
Petr
> boot_delay_msec(level);
> printk_delay();
> @@ -1652,6 +1659,11 @@ asmlinkage int vprintk_emit(int facility, int level,
> local_irq_save(flags);
> this_cpu = smp_processor_id();
>
> + if (level == SCHED_MESSAGE_LOGLEVEL) {
> + level = -1;
> + in_sched = true;
> + }
> +
> /*
> * Ouch, printk recursed into itself!
> */
> @@ -1789,7 +1801,7 @@ asmlinkage int vprintk_emit(int facility, int level,
>
> return printed_len;
> }
> -EXPORT_SYMBOL(vprintk_emit);
> +EXPORT_SYMBOL(printk_emit_string);
>
> asmlinkage int vprintk(const char *fmt, va_list args)
> {
> --
> 1.8.5.2
>
> --
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