If the log ring buffer becomes full, we silently overwrite old messages with new data. console_unlock will detect this case and fast-forward the console_* pointers to skip over the corrupted data, but nothing will be reported to the user.
This patch hijacks the first valid log message after detecting that we dropped messages and prefixes it with a note detailing how many messages were dropped. For long (~1000 char) messages, this will result in some truncation of the real message, but given that we're dropping things anyway, that doesn't seem to be the end of the world. Cc: Andrew Morton <[email protected]> Cc: Kay Sievers <[email protected]> Cc: Peter Zijlstra <[email protected]> Signed-off-by: Will Deacon <[email protected]> --- kernel/printk/printk.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 721a7d8fb853..e9e83d627ff0 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2046,10 +2046,15 @@ again_noirq: } if (console_seq < log_first_seq) { + len = sprintf(text, "** %u printk messages dropped ** ", + (unsigned)(log_first_seq - console_seq)); + /* messages are gone, move to first one */ console_seq = log_first_seq; console_idx = log_first_idx; console_prev = 0; + } else { + len = 0; } skip: if (console_seq == log_next_seq) @@ -2074,8 +2079,8 @@ skip: } level = msg->level; - len = msg_print_text(msg, console_prev, false, - text, sizeof(text)); + len += msg_print_text(msg, console_prev, false, + text + len, sizeof(text) - len); console_idx = log_next(console_idx); console_seq++; console_prev = msg->flags; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
