From 84b5ec8a9df86f3dcaaaf912715db35e4852d1da Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 4 Jun 2014 16:11:45 -0700 Subject: [PATCH] printk: report dropping of messages from logbuf 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. Signed-off-by: Will Deacon Acked-by: Peter Zijlstra Cc: Kay Sievers Cc: Jan Kara Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 35d9db251903..923c5d4e4202 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2157,10 +2157,15 @@ again: } 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) @@ -2185,8 +2190,8 @@ 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;