On 2021-01-29, Petr Mladek <pmla...@suse.com> wrote: >> diff --git a/include/linux/printk.h b/include/linux/printk.h >> index fe7eb2351610..6d8f844bfdff 100644 >> --- a/include/linux/printk.h >> +++ b/include/linux/printk.h >> @@ -45,6 +45,7 @@ static inline const char *printk_skip_headers(const char >> *buffer) >> } >> >> #define CONSOLE_EXT_LOG_MAX 8192 >> +#define CONSOLE_LOG_MAX 1024 >> >> /* printk's without a loglevel use this.. */ >> #define MESSAGE_LOGLEVEL_DEFAULT CONFIG_MESSAGE_LOGLEVEL_DEFAULT >> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c >> index ec2174882b8e..5faf9c0db171 100644 >> --- a/kernel/printk/printk.c >> +++ b/kernel/printk/printk.c >> @@ -410,7 +410,7 @@ static u64 clear_seq; >> #else >> #define PREFIX_MAX 32 >> #endif >> -#define LOG_LINE_MAX (1024 - PREFIX_MAX) >> +#define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX) > > CONSOLE_LOG_MAX defines size of buffers that are written by > record_print_text(). We must make sure that all stored > messages can actually get printed even with the trailing '\0'. > > We should limit the stored messages by: > > /* > * Console log buffer needs extra space for the trailing '\0', > * see reccord_print_text(). > */ > #define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX - 1) > > It should not be a big problem. The PREFIX_MAX size has already > increased in the patch, for example, because of the caller ID. > > Does it make sense, please?
If we want to make sure "all stored messages can actually get printed", then CONSOLE_LOG_MAX needs to be set to: PREFIX_MAX * LOG_LINE_MAX + 1 and we should be specifying LOG_LINE_MAX instead of CONSOLE_LOG_MAX. record_print_text() adds up to PREFIX_MAX for every '\n' in the message. I was initially confused by this, which led to my patch [0] to fix it. But then I realized that the buffer is way too small anyway. If we want to fix the issue, then LOG_LINE_MAX needs to be much larger. IMO it makes no sense to do the -1 change because the buffer is too small anyway. John Ogness [0] https://lkml.kernel.org/r/20210120194106.26441-2-john.ogn...@linutronix.de
