Changeset 90dd8aee in mainline

Timestamp:

2025-04-10T17:55:36Z (3 days ago)

Author:

Jiří Zárevúcky <zarevucky.jiri@…>

Branches:

master

Children:

8165a7a, c0d814a

Parents:

c55ab66

git-author:

Jiří Zárevúcky <zarevucky.jiri@…> (2025-04-10 11:33:46)

git-committer:

Jiří Zárevúcky <zarevucky.jiri@…> (2025-04-10 17:55:36)

Message:

Introduce a console lock to prevent line splitting in kernel output

It is a common occurrence to see broken lines on screen or in serial
output due to bad timing. This is an attempt to prevent that without
breaking anything.

It could be considered a stopgap solution, since the whole console
stack deserves a better/faster implementation.

Location:

kernel/generic

Files:

• include/console/console.h (modified) (1 diff)
• src/console/console.c (modified) (3 diffs)
• src/log/log.c (modified) (2 diffs)
• src/printf/vprintf.c (modified) (4 diffs)

kernel/generic/include/console/console.h

@@ -76 +76 @@
 extern sysarg_t sys_debug_console(void);
 
+extern void console_lock(void);
+extern void console_unlock(void);
+
 #endif /* KERN_CONSOLE_H_ */
 

kernel/generic/src/console/console.c

@@ -34 +34 @@
  */
 
+#include <abi/kio.h>
+#include <arch.h>
 #include <assert.h>
+#include <atomic.h>
+#include <console/chardev.h>
 #include <console/console.h>
-#include <console/chardev.h>
-#include <sysinfo/sysinfo.h>
-#include <synch/waitq.h>
-#include <synch/spinlock.h>
-#include <typedefs.h>
+#include <ddi/ddi.h>
 #include <ddi/irq.h>
-#include <ddi/ddi.h>
+#include <errno.h>
 #include <ipc/event.h>
 #include <ipc/irq.h>
-#include <arch.h>
+#include <mm/frame.h> /* SIZE2FRAMES */
 #include <panic.h>
+#include <preemption.h>
+#include <proc/thread.h>
+#include <putchar.h>
+#include <stdatomic.h>
 #include <stdio.h>
-#include <putchar.h>
-#include <atomic.h>
+#include <stdlib.h>  /* malloc */
+#include <str.h>
+#include <synch/mutex.h>
+#include <synch/spinlock.h>
+#include <synch/waitq.h>
 #include <syscall/copy.h>
-#include <errno.h>
-#include <str.h>
-#include <stdatomic.h>
-#include <abi/kio.h>
-#include <mm/frame.h> /* SIZE2FRAMES */
-#include <stdlib.h>  /* malloc */
+#include <sysinfo/sysinfo.h>
+#include <typedefs.h>
 
 #define KIO_PAGES    8
@@ -66 +69 @@
 /** Kernel log initialized */
 static atomic_bool kio_inited = ATOMIC_VAR_INIT(false);
+
+/** A mutex for preventing interleaving of output lines from different threads.
+ * May not be held in some circumstances, so locking of any internal shared
+ * structures is still necessary.
+ */
+static MUTEX_INITIALIZE(console_mutex, MUTEX_RECURSIVE);
 
 /** First kernel log characters */
@@ -395 +404 @@
 }
 
+/** Lock console output, ensuring that lines from different threads don't
+ * interleave. Does nothing when preemption is disabled, so that debugging
+ * and error printouts in sensitive areas still work.
+ */
+void console_lock(void)
+{
+        if (!PREEMPTION_DISABLED)
+                mutex_lock(&console_mutex);
+}
+
+/** Unlocks console output. See console_lock()
+ */
+void console_unlock(void)
+{
+        if (!PREEMPTION_DISABLED)
+                mutex_unlock(&console_mutex);
+}
+
 /** @}
  */

kernel/generic/src/log/log.c

@@ -151 +151 @@
 void log_begin(log_facility_t fac, log_level_t level)
 {
+        console_lock();
         spinlock_lock(&log_lock);
         spinlock_lock(&kio_lock);
@@ -186 +187 @@
         kio_update(NULL);
         log_update(NULL);
+        console_unlock();
 }
 

kernel/generic/src/printf/vprintf.c

@@ -33 +33 @@
  */
 
+#include <arch/asm.h>
+#include <console/console.h>
 #include <print.h>
 #include <printf/printf_core.h>
 #include <putchar.h>
+#include <str.h>
 #include <synch/spinlock.h>
-#include <arch/asm.h>
 #include <typedefs.h>
-#include <str.h>
 
 static int vprintf_str_write(const char *str, size_t size, void *data)
@@ -74 +75 @@
         char32_t uc;
 
+        console_lock();
+
         while ((uc = str_decode(str, &offset, STR_NO_LIMIT)) != 0) {
                 putuchar(uc);
@@ -80 +83 @@
 
         putuchar('\n');
+
+        console_unlock();
         return chars;
 }
@@ -91 +96 @@
         };
 
-        return printf_core(fmt, &ps, ap);
+        console_lock();
+        int ret = printf_core(fmt, &ps, ap);
+        console_unlock();
+        return ret;
 }