printk: move printk_info into separate array

The majority of the size of a descriptor is taken up by meta data,
which is often not of interest to the ringbuffer (for example,
when performing state checks). Since descriptors are often
temporarily stored on the stack, keeping their size minimal will
help reduce stack pressure.

Rather than embedding the printk_info into the descriptor, create
a separate printk_info array. The index of a descriptor in the
descriptor array corresponds to the printk_info with the same
index in the printk_info array. The rules for validity of a
printk_info match the existing rules for the data blocks: the
descriptor must be in a consistent state.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200918223421.21621-2-john.ogness@linutronix.de

Author: jogness

kernel/printk/printk.c

@@ -959,11 +959,11 @@ void log_buf_vmcoreinfo_setup(void)
 	VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
 	VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
 	VMCOREINFO_OFFSET(prb_desc_ring, descs);
+	VMCOREINFO_OFFSET(prb_desc_ring, infos);
 	VMCOREINFO_OFFSET(prb_desc_ring, head_id);
 	VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
 
 	VMCOREINFO_STRUCT_SIZE(prb_desc);
-	VMCOREINFO_OFFSET(prb_desc, info);
 	VMCOREINFO_OFFSET(prb_desc, state_var);
 	VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
 	VMCOREINFO_OFFSET(prb_desc, dict_blk_lpos);
@@ -1097,11 +1097,13 @@ static char setup_dict_buf[CONSOLE_EXT_LOG_MAX] __initdata;
 
 void __init setup_log_buf(int early)
 {
+	struct printk_info *new_infos;
 	unsigned int new_descs_count;
 	struct prb_desc *new_descs;
 	struct printk_info info;
 	struct printk_record r;
 	size_t new_descs_size;
+	size_t new_infos_size;
 	unsigned long flags;
 	char *new_dict_buf;
 	char *new_log_buf;
@@ -1142,18 +1144,23 @@ void __init setup_log_buf(int early)
 	if (unlikely(!new_dict_buf)) {
 		pr_err("log_buf_len: %lu dict bytes not available\n",
 		       new_log_buf_len);
-		memblock_free(__pa(new_log_buf), new_log_buf_len);
-		return;
+		goto err_free_log_buf;
 	}
 
 	new_descs_size = new_descs_count * sizeof(struct prb_desc);
 	new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
 	if (unlikely(!new_descs)) {
 		pr_err("log_buf_len: %zu desc bytes not available\n",
 		       new_descs_size);
-		memblock_free(__pa(new_dict_buf), new_log_buf_len);
-		memblock_free(__pa(new_log_buf), new_log_buf_len);
-		return;
+		goto err_free_dict_buf;
+	}
+
+	new_infos_size = new_descs_count * sizeof(struct printk_info);
+	new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
+	if (unlikely(!new_infos)) {
+		pr_err("log_buf_len: %zu info bytes not available\n",
+		       new_infos_size);
+		goto err_free_descs;
 	}
 
 	prb_rec_init_rd(&r, &info,
@@ -1163,7 +1170,8 @@ void __init setup_log_buf(int early)
 	prb_init(&printk_rb_dynamic,
 		 new_log_buf, ilog2(new_log_buf_len),
 		 new_dict_buf, ilog2(new_log_buf_len),
-		 new_descs, ilog2(new_descs_count));
+		 new_descs, ilog2(new_descs_count),
+		 new_infos);
 
 	logbuf_lock_irqsave(flags);
 
@@ -1192,6 +1200,14 @@ void __init setup_log_buf(int early)
 	pr_info("log_buf_len: %u bytes\n", log_buf_len);
 	pr_info("early log buf free: %u(%u%%)\n",
 		free, (free * 100) / __LOG_BUF_LEN);
+	return;
+
+err_free_descs:
+	memblock_free(__pa(new_descs), new_descs_size);
+err_free_dict_buf:
+	memblock_free(__pa(new_dict_buf), new_log_buf_len);
+err_free_log_buf:
+	memblock_free(__pa(new_log_buf), new_log_buf_len);
 }
 
 static bool __read_mostly ignore_loglevel;