Commit 39b25109 authored by Petr Mladek's avatar Petr Mladek Committed by Linus Torvalds
Browse files

printk: use also the last bytes in the ring buffer



It seems that we have newer used the last byte in the ring buffer.  In
fact, we have newer used the last 4 bytes because of padding.

First problem is in the check for free space.  The exact number of free
bytes is enough to store the length of data.

Second problem is in the check where the ring buffer is rotated.  The
left side counts the first unused index.  It is unused, so it might be
the same as the size of the buffer.

Note that the first problem has to be fixed together with the second
one.  Otherwise, the buffer is rotated even when there is enough space
on the end of the buffer.  Then the beginning of the buffer is rewritten
and valid entries get corrupted.
Signed-off-by: default avatarPetr Mladek <pmladek@suse.cz>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Kay Sievers <kay@vrfy.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e8c42d36
......@@ -319,7 +319,7 @@ static void log_store(int facility, int level,
else
free = log_first_idx - log_next_idx;
if (free > size + sizeof(struct printk_log))
if (free >= size + sizeof(struct printk_log))
break;
/* drop old messages until we have enough contiuous space */
......@@ -327,7 +327,7 @@ static void log_store(int facility, int level,
log_first_seq++;
}
if (log_next_idx + size + sizeof(struct printk_log) >= log_buf_len) {
if (log_next_idx + size + sizeof(struct printk_log) > log_buf_len) {
/*
* This message + an additional empty header does not fit
* at the end of the buffer. Add an empty header with len == 0
......
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