@@ -572,7 +572,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
struct printk_log *msg;
u64 ts_usec;
size_t i;
- char cont = '-';
+ char cont;
size_t len;
ssize_t ret;
@@ -619,11 +619,12 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
* better readable output. 'c' in the record flags mark the first
* fragment of a line, '+' the following.
*/
- if (msg->flags & LOG_CONT && !(user->prev & LOG_CONT))
- cont = 'c';
- else if ((msg->flags & LOG_CONT) ||
- ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX)))
+ if ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX))
cont = '+';
+ else if (msg->flags & LOG_CONT)
+ cont = 'c';
+ else
+ cont = '-';
len = sprintf(user->buf, "%u,%llu,%llu,%c;",
(msg->facility << 3) | msg->level,
In devkmsg_read(), a variable "cont" holds a character that's used to indicate whether a given log line is a "continuation", that is, whether a log record should be merged with the one before or after it. If a record should be merged with its successor (but not its predecessor) that character is 'c'. And the line following such a 'c' log record is normally marked with a '+' to show it is continues its predecessor. Any other cases are marked '-', indicating the log record stands on its own. There is an exception. If a log record is marked LOG_PREFIX, it indicates that this record represents a new log entry, implicitly terminating the predecessor--even if the predecessor would otherwise have been continued. So a record marked LOG_PREFIX (that is not also marked LOG_CONT) should have '-' for its "cont" variable. The logic that determines this "continuation" character has a bug that gets that exceptional case wrong. The specific case that produces the wrong result is when all of these conditions are non-zero: user->prev & LOG_CONT msg->flags & LOG_PREFIX msg->flags & LOG_CONT The bug is that despite the message's LOG_PREFIX flag, the "cont" character is getting set to '+' rather than 'c'. The problem is that the message's LOG_PREFIX flag is getting ignored if its LOG_CONT flag is also set. Rearrange the logic here to produce the correct result. The following table concisely defines the problem: prev | msg | msg ||"cont" CONT |PREFIX| CONT || char ------+------+------++------ clear| clear| clear|| '-' clear| clear| set || 'c' clear| set | clear|| '-' clear| set | set || 'c' set | clear| clear|| '+' set | clear| set || '+' set | set | clear|| '-' set | set | set || '+' <-- should be 'c' Signed-off-by: Alex Elder <elder@linaro.org> Reviewed-by: Petr Mladek <pmladek@suse.cz> --- kernel/printk/printk.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)