@@ -242,6 +242,7 @@ struct printk_buffers;
* be used only with NBCON_PRIO_PANIC @prio. It
* might cause a system freeze when the console
* is used later.
+ * @backlog: Ringbuffer has pending records
* @pbufs: Pointer to the text buffer for this context
* @seq: The sequence number to print for this context
*/
@@ -252,11 +253,28 @@ struct nbcon_context {
enum nbcon_prio prio;
unsigned int allow_unsafe_takeover : 1;
+ /* members set by emit */
+ unsigned int backlog : 1;
+
/* members set by acquire */
struct printk_buffers *pbufs;
u64 seq;
};
+/**
+ * struct nbcon_write_context - Context handed to the nbcon write callbacks
+ * @ctxt: The core console context
+ * @outbuf: Pointer to the text buffer for output
+ * @len: Length to write
+ * @unsafe_takeover: If a hostile takeover in an unsafe state has occurred
+ */
+struct nbcon_write_context {
+ struct nbcon_context __private ctxt;
+ char *outbuf;
+ unsigned int len;
+ bool unsafe_takeover;
+};
+
/**
* struct console - The console descriptor structure
* @name: The name of the console driver
@@ -277,6 +295,7 @@ struct nbcon_context {
* @data: Driver private data
* @node: hlist node for the console list
*
+ * @write_atomic: Write callback for atomic context
* @nbcon_state: State for nbcon consoles
* @nbcon_seq: Sequence number of the next record for nbcon to print
* @pbufs: Pointer to nbcon private buffer
@@ -301,6 +320,8 @@ struct console {
struct hlist_node node;
/* nbcon console specific members */
+ bool (*write_atomic)(struct console *con,
+ struct nbcon_write_context *wctxt);
atomic_t __private nbcon_state;
atomic_long_t __private nbcon_seq;
struct printk_buffers *pbufs;
@@ -130,3 +130,9 @@ struct printk_message {
};
bool other_cpu_in_panic(void);
+bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
+ bool is_extended, bool may_supress);
+
+#ifdef CONFIG_PRINTK
+void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped);
+#endif
@@ -221,7 +221,6 @@ void nbcon_seq_force(struct console *con, u64 seq)
* nbcon_seq_force() was used or the current context no longer owns the
* console. In the later case, it will stop printing anyway.
*/
-__maybe_unused
static void nbcon_seq_try_update(struct nbcon_context *ctxt, u64 new_seq)
{
unsigned long nbcon_seq = __seq_to_nbcon_seq(ctxt->seq);
@@ -755,7 +754,6 @@ static bool nbcon_context_can_proceed(struct nbcon_context *ctxt, struct nbcon_s
*
* Internal helper to avoid duplicated code.
*/
-__maybe_unused
static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsafe)
{
struct console *con = ctxt->console;
@@ -784,6 +782,110 @@ static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsaf
return nbcon_context_can_proceed(ctxt, &cur);
}
+/**
+ * nbcon_emit_next_record - Emit a record in the acquired context
+ * @wctxt: The write context that will be handed to the write function
+ *
+ * Return: True if this context still owns the console. False if
+ * ownership was handed over or taken.
+ *
+ * When this function returns false then the calling context no longer owns
+ * the console and is no longer allowed to go forward. In this case it must
+ * back out immediately and carefully. The buffer content is also no longer
+ * trusted since it no longer belongs to the calling context. If the caller
+ * wants to do more it must reacquire the console first.
+ *
+ * When true is returned, @wctxt->ctxt.backlog indicates whether there are
+ * still records pending in the ringbuffer,
+ */
+__maybe_unused
+static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
+{
+ struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+ struct console *con = ctxt->console;
+ bool is_extended = console_srcu_read_flags(con) & CON_EXTENDED;
+ struct printk_message pmsg = {
+ .pbufs = ctxt->pbufs,
+ };
+ unsigned long con_dropped;
+ struct nbcon_state cur;
+ unsigned long dropped;
+ bool done;
+
+ /*
+ * The printk buffers are filled within an unsafe section. This
+ * prevents NBCON_PRIO_NORMAL and NBCON_PRIO_EMERGENCY from
+ * clobbering each other.
+ */
+
+ if (!nbcon_context_enter_unsafe(ctxt))
+ return false;
+
+ ctxt->backlog = printk_get_next_message(&pmsg, ctxt->seq, is_extended, true);
+ if (!ctxt->backlog)
+ return nbcon_context_exit_unsafe(ctxt);
+
+ /*
+ * @con->dropped is not protected in case of an unsafe hostile
+ * takeover. In that situation the update can be racy so
+ * annotate it accordingly.
+ */
+ con_dropped = data_race(READ_ONCE(con->dropped));
+
+ dropped = con_dropped + pmsg.dropped;
+ if (dropped && !is_extended)
+ console_prepend_dropped(&pmsg, dropped);
+
+ if (!nbcon_context_exit_unsafe(ctxt))
+ return false;
+
+ /* For skipped records just update seq/dropped in @con. */
+ if (pmsg.outbuf_len == 0)
+ goto update_con;
+
+ /* Initialize the write context for driver callbacks. */
+ wctxt->outbuf = &pmsg.pbufs->outbuf[0];
+ wctxt->len = pmsg.outbuf_len;
+ nbcon_state_read(con, &cur);
+ wctxt->unsafe_takeover = cur.unsafe_takeover;
+
+ if (con->write_atomic) {
+ done = con->write_atomic(con, wctxt);
+ } else {
+ nbcon_context_release(ctxt);
+ WARN_ON_ONCE(1);
+ done = false;
+ }
+
+ /* If not done, the emit was aborted. */
+ if (!done)
+ return false;
+
+ /*
+ * Since any dropped message was successfully output, reset the
+ * dropped count for the console.
+ */
+ dropped = 0;
+update_con:
+ /*
+ * The dropped count and the sequence number are updated within an
+ * unsafe section. This limits update races to the panic context and
+ * allows the panic context to win.
+ */
+
+ if (!nbcon_context_enter_unsafe(ctxt))
+ return false;
+
+ if (dropped != con_dropped) {
+ /* Counterpart to the READ_ONCE() above. */
+ WRITE_ONCE(con->dropped, dropped);
+ }
+
+ nbcon_seq_try_update(ctxt, pmsg.seq + 1);
+
+ return nbcon_context_exit_unsafe(ctxt);
+}
+
/**
* nbcon_alloc - Allocate buffers needed by the nbcon console
* @con: Console to allocate buffers for
@@ -698,9 +698,6 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
return len;
}
-static bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
- bool is_extended, bool may_supress);
-
/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
atomic64_t seq;
@@ -2733,7 +2730,7 @@ static void __console_unlock(void)
* If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
*/
#ifdef CONFIG_PRINTK
-static void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
+void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
{
struct printk_buffers *pbufs = pmsg->pbufs;
const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
@@ -2787,8 +2784,8 @@ static void console_prepend_dropped(struct printk_message *pmsg, unsigned long d
* of @pmsg are valid. (See the documentation of struct printk_message
* for information about the @pmsg fields.)
*/
-static bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
- bool is_extended, bool may_suppress)
+bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
+ bool is_extended, bool may_suppress)
{
static int panic_console_dropped;