printk: split code for making free space in the log buffer (0a581694) · Commits · 戴 / test

The check for free space in the log buffer always passes when "first_seq" and "next_seq" are equal. In theory, it might cause writing outside of the log buffer. Fortunately, the current usage looks safe because the used "text" and "dict" buffers are quite limited. See the second patch for more details. Anyway, it is better to be on the safe side and add a check. An easy solution is done in the 2nd patch and it is improved in the 4th patch. 5th patch fixes the computation of the printed message length. 1st and 3rd patches just do some code refactoring to make the other patches easier. This patch (of 5): There will be needed some fixes in the check for free space. They will be easier if the code is moved outside of the quite long log_store() function. This patch does not change the existing behavior. Signed-off-by:

Petr Mladek <pmladek@suse.cz> Cc: Jan Kara <jack@suse.cz> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Kay Sievers <kay@vrfy.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/printk/printk.c

+29 −15

Original line number	Diff line number	Diff line
		@@ -297,6 +297,34 @@ static u32 log_next(u32 idx)
		return idx + msg->len;
		}

		/* check whether there is enough free space for the given message */
		static int logbuf_has_space(u32 msg_size)
		{
		u32 free;

		if (log_next_idx > log_first_idx)
		free = max(log_buf_len - log_next_idx, log_first_idx);
		else
		free = log_first_idx - log_next_idx;

		/*
		* We need space also for an empty header that signalizes wrapping
		* of the buffer.
		*/
		return free >= msg_size + sizeof(struct printk_log);
		}

		static void log_make_free_space(u32 msg_size)
		{
		while (log_first_seq < log_next_seq) {
		if (logbuf_has_space(msg_size))
		return;
		/* drop old messages until we have enough continuous space */
		log_first_idx = log_next(log_first_idx);
		log_first_seq++;
		}
		}

		/* insert record into the buffer, discard old ones, update heads */
		static void log_store(int facility, int level,
		enum log_flags flags, u64 ts_nsec,
		@@ -311,21 +339,7 @@ static void log_store(int facility, int level,
		pad_len = (-size) & (LOG_ALIGN - 1);
		size += pad_len;

		while (log_first_seq < log_next_seq) {
		u32 free;

		if (log_next_idx > log_first_idx)
		free = max(log_buf_len - log_next_idx, log_first_idx);
		else
		free = log_first_idx - log_next_idx;

		if (free >= size + sizeof(struct printk_log))
		break;

		/* drop old messages until we have enough contiuous space */
		log_first_idx = log_next(log_first_idx);
		log_first_seq++;
		}
		log_make_free_space(size);

		if (log_next_idx + size + sizeof(struct printk_log) > log_buf_len) {
		/*

Admin message