printk: Add caller information to printk() output.

Sometimes we want to print a series of printk() messages to consoles
without being disturbed by concurrent printk() from interrupts and/or
other threads. But we can't enforce printk() callers to use their local
buffers because we need to ask them to make too much changes. Also, even
buffering up to one line inside printk() might cause failing to emit
an important clue under critical situation.

Therefore, instead of trying to help buffering, let's try to help
reconstructing messages by saving caller information as of calling
log_store() and adding it as "[T$thread_id]" or "[C$processor_id]"
upon printing to consoles.

Some examples for console output:

  [    1.222773][    T1] x86: Booting SMP configuration:
  [    2.779635][    T1] pci 0000:00:01.0: PCI bridge to [bus 01]
  [    5.069193][  T268] Fusion MPT base driver 3.04.20
  [    9.316504][    C2] random: fast init done
  [   13.413336][ T3355] Initialized host personality

Some examples for /dev/kmsg output:

  6,496,1222773,-,caller=T1;x86: Booting SMP configuration:
  6,968,2779635,-,caller=T1;pci 0000:00:01.0: PCI bridge to [bus 01]
   SUBSYSTEM=pci
   DEVICE=+pci:0000:00:01.0
  6,1353,5069193,-,caller=T268;Fusion MPT base driver 3.04.20
  5,1526,9316504,-,caller=C2;random: fast init done
  6,1575,13413336,-,caller=T3355;Initialized host personality

Note that this patch changes max length of messages which can be printed
by printk() or written to /dev/kmsg interface from 992 bytes to 976 bytes,
based on an assumption that userspace won't try to write messages hitting
that border line to /dev/kmsg interface.

Link: http://lkml.kernel.org/r/93f19e57-5051-c67d-9af4-b17624062d44@i-love.sakura.ne.jp
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>

1 files changed, 51 insertions, 4 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 91db332ccf4d..e3d977bbc7ab 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -357,6 +357,9 @@ struct printk_log {
         u8 facility;            /* syslog facility */
         u8 flags:5;             /* internal record flags */
         u8 level:3;             /* syslog level */
+#ifdef CONFIG_PRINTK_CALLER
+        u32 caller_id;            /* thread id or processor id */
+#endif
 }
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 __packed __aligned(4)
@@ -423,7 +426,11 @@ static u64 exclusive_console_stop_seq;
 static u64 clear_seq;
 static u32 clear_idx;
 
+#ifdef CONFIG_PRINTK_CALLER
+#define PREFIX_MAX              48
+#else
 #define PREFIX_MAX              32
+#endif
 #define LOG_LINE_MAX            (1024 - PREFIX_MAX)
 
 #define LOG_LEVEL(v)            ((v) & 0x07)
@@ -626,6 +633,12 @@ static int log_store(int facility, int level,
                 msg->ts_nsec = ts_nsec;
         else
                 msg->ts_nsec = local_clock();
+#ifdef CONFIG_PRINTK_CALLER
+        if (in_task())
+                msg->caller_id = task_pid_nr(current);
+        else
+                msg->caller_id = 0x80000000 + raw_smp_processor_id();
+#endif
         memset(log_dict(msg) + dict_len, 0, pad_len);
         msg->len = size;
 
@@ -689,12 +702,21 @@ static ssize_t msg_print_ext_header(char *buf, size_t size,
                                     struct printk_log *msg, u64 seq)
 {
         u64 ts_usec = msg->ts_nsec;
+        char caller[20];
+#ifdef CONFIG_PRINTK_CALLER
+        u32 id = msg->caller_id;
+
+        snprintf(caller, sizeof(caller), ",caller=%c%u",
+                 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
+#else
+        caller[0] = '\0';
+#endif
 
         do_div(ts_usec, 1000);
 
-        return scnprintf(buf, size, "%u,%llu,%llu,%c;",
-                       (msg->facility << 3) | msg->level, seq, ts_usec,
-                       msg->flags & LOG_CONT ? 'c' : '-');
+        return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
+                         (msg->facility << 3) | msg->level, seq, ts_usec,
+                         msg->flags & LOG_CONT ? 'c' : '-', caller);
 }
 
 static ssize_t msg_print_ext_body(char *buf, size_t size,
@@ -1039,6 +1061,9 @@ void log_buf_vmcoreinfo_setup(void)
         VMCOREINFO_OFFSET(printk_log, len);
         VMCOREINFO_OFFSET(printk_log, text_len);
         VMCOREINFO_OFFSET(printk_log, dict_len);
+#ifdef CONFIG_PRINTK_CALLER
+        VMCOREINFO_OFFSET(printk_log, caller_id);
+#endif
 }
 #endif
 
@@ -1237,10 +1262,23 @@ static size_t print_time(u64 ts, char *buf)
 {
         unsigned long rem_nsec = do_div(ts, 1000000000);
 
-        return sprintf(buf, "[%5lu.%06lu] ",
+        return sprintf(buf, "[%5lu.%06lu]",
                        (unsigned long)ts, rem_nsec / 1000);
 }
 
+#ifdef CONFIG_PRINTK_CALLER
+static size_t print_caller(u32 id, char *buf)
+{
+        char caller[12];
+
+        snprintf(caller, sizeof(caller), "%c%u",
+                 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
+        return sprintf(buf, "[%6s]", caller);
+}
+#else
+#define print_caller(id, buf) 0
+#endif
+
 static size_t print_prefix(const struct printk_log *msg, bool syslog,
                            bool time, char *buf)
 {
@@ -1248,8 +1286,17 @@ static size_t print_prefix(const struct printk_log *msg, bool syslog,
 
         if (syslog)
                 len = print_syslog((msg->facility << 3) | msg->level, buf);
+
         if (time)
                 len += print_time(msg->ts_nsec, buf + len);
+
+        len += print_caller(msg->caller_id, buf + len);
+
+        if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
+                buf[len++] = ' ';
+                buf[len] = '\0';
+        }
+
         return len;
 }