printk: nbcon: Add context to usable() and emit()

The nbcon consoles will have two callbacks to be used for
different contexts. In order to determine if an nbcon console
is usable, console_is_usable() must know if it is a context
that will need to use the optional write_atomic() callback.
Also, nbcon_emit_next_record() must know which callback it
needs to call.

Add an extra parameter @use_atomic to console_is_usable() and
nbcon_emit_next_record() to specify this.

Since so far only the write_atomic() callback exists,
@use_atomic is set to true for all call sites.

For legacy consoles, @use_atomic is not used.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240904120536.115780-5-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 8e36d8695f817873c9d81a70df16751c11b74cfc..ad631824e7e5377f7a1f1cafb63aca67d1999e33 100644 (file)
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -97,7 +97,7 @@ bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
  * which can also play a role in deciding if @con can be used to print
  * records.
  */
-static inline bool console_is_usable(struct console *con, short flags)
+static inline bool console_is_usable(struct console *con, short flags, bool use_atomic)
 {
        if (!(flags & CON_ENABLED))
                return false;
@@ -106,7 +106,8 @@ static inline bool console_is_usable(struct console *con, short flags)
                return false;
 
        if (flags & CON_NBCON) {
-               if (!con->write_atomic)
+               /* The write_atomic() callback is optional. */
+               if (use_atomic && !con->write_atomic)
                        return false;
        } else {
                if (!con->write)
@@ -149,7 +150,8 @@ static inline void nbcon_atomic_flush_pending(void) { }
 static inline bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
                                                 int cookie) { return false; }
 
-static inline bool console_is_usable(struct console *con, short flags) { return false; }
+static inline bool console_is_usable(struct console *con, short flags,
+                                    bool use_atomic) { return false; }
 
 #endif /* CONFIG_PRINTK */
 

diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 8a1bf6f94bce2de4a74f818bf0c2c580d3df5bc3..88db24f9a8de40f897e2dc3b4f822521bd4f716e 100644 (file)
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -922,6 +922,7 @@ EXPORT_SYMBOL_GPL(nbcon_reacquire_nobuf);
 /**
  * nbcon_emit_next_record - Emit a record in the acquired context
  * @wctxt:     The write context that will be handed to the write function
+ * @use_atomic:        True if the write_atomic() callback is to be used
  *
  * Return:     True if this context still owns the console. False if
  *             ownership was handed over or taken.
@@ -935,7 +936,7 @@ EXPORT_SYMBOL_GPL(nbcon_reacquire_nobuf);
  * When true is returned, @wctxt->ctxt.backlog indicates whether there are
  * still records pending in the ringbuffer,
  */
-static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
+static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt, bool use_atomic)
 {
        struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
        struct console *con = ctxt->console;
@@ -946,6 +947,18 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
        unsigned long con_dropped;
        unsigned long dropped;
 
+       /*
+        * This function should never be called for consoles that have not
+        * implemented the necessary callback for writing: i.e. legacy
+        * consoles and, when atomic, nbcon consoles with no write_atomic().
+        * Handle it as if ownership was lost and try to continue.
+        */
+       if (WARN_ON_ONCE((use_atomic && !con->write_atomic) ||
+                        !(console_srcu_read_flags(con) & CON_NBCON))) {
+               nbcon_context_release(ctxt);
+               return false;
+       }
+
        /*
         * The printk buffers are filled within an unsafe section. This
         * prevents NBCON_PRIO_NORMAL and NBCON_PRIO_EMERGENCY from
@@ -980,17 +993,8 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
        /* Initialize the write context for driver callbacks. */
        nbcon_write_context_set_buf(wctxt, &pmsg.pbufs->outbuf[0], pmsg.outbuf_len);
 
-       if (con->write_atomic) {
+       if (use_atomic)
                con->write_atomic(con, wctxt);
-       } else {
-               /*
-                * This function should never be called for legacy consoles.
-                * Handle it as if ownership was lost and try to continue.
-                */
-               WARN_ON_ONCE(1);
-               nbcon_context_release(ctxt);
-               return false;
-       }
 
        if (!wctxt->outbuf) {
                /*
@@ -1118,7 +1122,7 @@ static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)
         * The higher priority printing context takes over responsibility
         * to print the pending records.
         */
-       if (!nbcon_emit_next_record(wctxt))
+       if (!nbcon_emit_next_record(wctxt, true))
                return false;
 
        nbcon_context_release(ctxt);
@@ -1219,7 +1223,7 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq,
                 * handed over or taken over. In both cases the context is no
                 * longer valid.
                 */
-               if (!nbcon_emit_next_record(&wctxt))
+               if (!nbcon_emit_next_record(&wctxt, true))
                        return -EAGAIN;
 
                if (!ctxt->backlog) {
@@ -1305,7 +1309,7 @@ static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_takeove
                if (!(flags & CON_NBCON))
                        continue;
 
-               if (!console_is_usable(con, flags))
+               if (!console_is_usable(con, flags, true))
                        continue;
 
                if (nbcon_seq_read(con) >= stop_seq)
@@ -1490,7 +1494,7 @@ void nbcon_device_release(struct console *con)
         * the console is usable throughout flushing.
         */
        cookie = console_srcu_read_lock();
-       if (console_is_usable(con, console_srcu_read_flags(con)) &&
+       if (console_is_usable(con, console_srcu_read_flags(con), true) &&
            prb_read_valid(prb, nbcon_seq_read(con), NULL)) {
                /*
                 * If nbcon_atomic flushing is not available, fallback to

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c79e962b822ad59c1dc34245457843aab2935855..846306ac26631e5da5355aeab94cf12001e20cee 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3071,7 +3071,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
                        u64 printk_seq;
                        bool progress;
 
-                       if (!console_is_usable(con, flags))
+                       if (!console_is_usable(con, flags, true))
                                continue;
                        any_usable = true;
 
@@ -3773,7 +3773,7 @@ static int unregister_console_locked(struct console *console)
 
        if (!console_is_registered_locked(console))
                res = -ENODEV;
-       else if (console_is_usable(console, console->flags))
+       else if (console_is_usable(console, console->flags, true))
                __pr_flush(console, 1000, true);
 
        /* Disable it unconditionally */
@@ -4043,7 +4043,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
                         * that they make forward progress, so only increment
                         * @diff for usable consoles.
                         */
-                       if (!console_is_usable(c, flags))
+                       if (!console_is_usable(c, flags, true))
                                continue;
 
                        if (flags & CON_NBCON) {