[PATCH] log: output logs of printk safe buffers

["shogo.matsumoto@xxxxxxxxxxx" <shogo.matsumoto@xxxxxxxxxxx>]

We sometimes overlook logs written to printk safe buffers
(safe_print_seq/nmi_print_seq) which have not been flushed yet.

This patch will output unflushed logs of the safe buffers
at the bottom of log command output as follows:

[nmi_print_seq] CPU: 0  BUFFER: ffff888063c18ac0  LEN: 28
nmi print seq test message
[safe_print_seq] CPU: 1  BUFFER: ffff888063d19ae0  LEN: 30
safe print seq test message

Note that the safe buffer (struct printk_safe_seq_buf) was introduced
in kernel-4.11 and removed in kernel-5.15.

Signed-off-by: Shogo Matsumoto <shogo.matsumoto@xxxxxxxxxxx>
---
 defs.h   |  3 +++
 kernel.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/defs.h b/defs.h
index 7e2a16e..3ee51e0 100644
--- a/defs.h
+++ b/defs.h
@@ -2146,6 +2146,8 @@ struct offset_table {                    /* stash of commonly-used offsets */
 	long wait_queue_entry_private;
 	long wait_queue_head_head;
 	long wait_queue_entry_entry;
+	long printk_safe_seq_buf_len;
+	long printk_safe_seq_buf_buffer;
 };
 
 struct size_table {         /* stash of commonly-used sizes */
@@ -2310,6 +2312,7 @@ struct size_table {         /* stash of commonly-used sizes */
 	long prb_desc;
 	long wait_queue_entry;
 	long task_struct_state;
+	long printk_safe_seq_buf_buffer;
 };
 
 struct array_table {
diff --git a/kernel.c b/kernel.c
index f4598ea..cc97176 100644
--- a/kernel.c
+++ b/kernel.c
@@ -93,6 +93,7 @@ static void source_tree_init(void);
 static ulong dump_audit_skb_queue(ulong);
 static ulong __dump_audit(char *);
 static void dump_audit(void);
+static void dump_printk_safe_seq_buf(void);
 static char *vmcoreinfo_read_string(const char *);
 static void check_vmcoreinfo(void);
 static int is_pvops_xen(void);
@@ -5048,6 +5049,7 @@ cmd_log(void)
 	}
 
 	dump_log(msg_flags);
+	dump_printk_safe_seq_buf();
 }
 
 
@@ -11534,6 +11536,62 @@ dump_audit(void)
 		error(INFO, "kernel audit log is empty\n");
 }
 
+static void
+__dump_printk_safe_seq_buf(char *buf_name)
+{
+	int cpu, buffer_size;
+	char *buffer;
+
+	if (!symbol_exists(buf_name)) {
+		return;
+	}
+
+	buffer_size = SIZE(printk_safe_seq_buf_buffer);
+	buffer = GETBUF(buffer_size);
+	for (cpu = 0; cpu < kt->cpus; cpu++) {
+		ulong len_addr, buffer_addr;
+		int len;
+
+		len_addr = symbol_value(buf_name) + kt->__per_cpu_offset[cpu] + OFFSET(printk_safe_seq_buf_len);
+		buffer_addr = symbol_value(buf_name) + kt->__per_cpu_offset[cpu] + OFFSET(printk_safe_seq_buf_buffer);
+		readmem(len_addr, KVADDR, &len, STRUCT_SIZE("atomic_t"), "printk_safe_seq_buf len", FAULT_ON_ERROR);
+		readmem(buffer_addr, KVADDR, buffer, buffer_size, "printk_safe_seq_buf buffer", FAULT_ON_ERROR);
+
+		if (len > 0) {
+			int i, n;
+			char *p;
+			fprintf(fp, "[%s] CPU: %d  BUFFER: %lx  LEN: %d\n", buf_name, cpu, buffer_addr, len);
+			n = (len <= buffer_size) ? len : buffer_size;
+			for (i = 0, p = buffer; i < n; i++, p++) {
+				if (*p == 0x1) { //SOH
+					i++; p++;
+					continue;
+				} else {
+					fputc(ascii(*p) ? *p : '.', fp);
+				}
+			}
+			fputc('\n', fp);
+		}
+	}
+	FREEBUF(buffer);
+}
+
+static void
+dump_printk_safe_seq_buf(void)
+{
+	if (!STRUCT_EXISTS("printk_safe_seq_buf"))
+		return;
+
+	if (INVALID_SIZE(printk_safe_seq_buf_buffer)) {
+		MEMBER_OFFSET_INIT(printk_safe_seq_buf_len, "printk_safe_seq_buf", "len");
+		MEMBER_OFFSET_INIT(printk_safe_seq_buf_buffer, "printk_safe_seq_buf", "buffer");
+		MEMBER_SIZE_INIT(printk_safe_seq_buf_buffer, "printk_safe_seq_buf", "buffer");
+	}
+
+	__dump_printk_safe_seq_buf("nmi_print_seq");
+	__dump_printk_safe_seq_buf("safe_print_seq");
+}
+
 /*
  * Reads a string value from the VMCOREINFO data stored in (live) memory.
  *
-- 
2.29.2



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