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-rw-r--r--debian/patches-rt/0081-printk-nbcon-Add-emit-function-and-callback-function.patch262
1 files changed, 262 insertions, 0 deletions
diff --git a/debian/patches-rt/0081-printk-nbcon-Add-emit-function-and-callback-function.patch b/debian/patches-rt/0081-printk-nbcon-Add-emit-function-and-callback-function.patch
new file mode 100644
index 0000000000..ab32a05b19
--- /dev/null
+++ b/debian/patches-rt/0081-printk-nbcon-Add-emit-function-and-callback-function.patch
@@ -0,0 +1,262 @@
+From: Thomas Gleixner <tglx@linutronix.de>
+Date: Sat, 16 Sep 2023 21:26:06 +0206
+Subject: [PATCH 081/134] printk: nbcon: Add emit function and callback
+ function for atomic printing
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
+
+Implement an emit function for nbcon consoles to output printk
+messages. It utilizes the lockless printk_get_next_message() and
+console_prepend_dropped() functions to retrieve/build the output
+message. The emit function includes the required safety points to
+check for handover/takeover and calls a new write_atomic callback
+of the console driver to output the message. It also includes
+proper handling for updating the nbcon console sequence number.
+
+A new nbcon_write_context struct is introduced. This is provided
+to the write_atomic callback and includes only the information
+necessary for performing atomic writes.
+
+Co-developed-by: John Ogness <john.ogness@linutronix.de>
+Signed-off-by: John Ogness <john.ogness@linutronix.de>
+Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de>
+Reviewed-by: Petr Mladek <pmladek@suse.com>
+Signed-off-by: Petr Mladek <pmladek@suse.com>
+Link: https://lore.kernel.org/r/20230916192007.608398-8-john.ogness@linutronix.de
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ include/linux/console.h | 21 +++++++++
+ kernel/printk/internal.h | 6 ++
+ kernel/printk/nbcon.c | 106 ++++++++++++++++++++++++++++++++++++++++++++++-
+ kernel/printk/printk.c | 9 +--
+ 4 files changed, 134 insertions(+), 8 deletions(-)
+
+--- a/include/linux/console.h
++++ b/include/linux/console.h
+@@ -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
+ */
+@@ -252,12 +253,29 @@ 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
+ * @write: Write callback to output messages (Optional)
+@@ -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;
+--- a/kernel/printk/internal.h
++++ b/kernel/printk/internal.h
+@@ -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
+--- a/kernel/printk/nbcon.c
++++ b/kernel/printk/nbcon.c
+@@ -221,7 +221,6 @@ void nbcon_seq_force(struct console *con
+ * 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(st
+ *
+ * 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;
+@@ -785,6 +783,110 @@ static bool __nbcon_context_update_unsaf
+ }
+
+ /**
++ * 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
+ *
+--- a/kernel/printk/printk.c
++++ b/kernel/printk/printk.c
+@@ -698,9 +698,6 @@ static ssize_t msg_print_ext_body(char *
+ 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(stru
+ * 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;
+