diff options
Diffstat (limited to 'debian/patches-rt/0010-console-Improve-console_srcu_read_flags-comments.patch')
| -rw-r--r-- | debian/patches-rt/0010-console-Improve-console_srcu_read_flags-comments.patch | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/debian/patches-rt/0010-console-Improve-console_srcu_read_flags-comments.patch b/debian/patches-rt/0010-console-Improve-console_srcu_read_flags-comments.patch new file mode 100644 index 0000000000..ea346ac04c --- /dev/null +++ b/debian/patches-rt/0010-console-Improve-console_srcu_read_flags-comments.patch @@ -0,0 +1,72 @@ +From: John Ogness <john.ogness@linutronix.de> +Date: Wed, 17 Apr 2024 14:34:50 +0000 +Subject: [PATCH 10/46] console: Improve console_srcu_read_flags() comments +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.9/older/patches-6.9-rt5.tar.xz + +It was not clear when exactly console_srcu_read_flags() must be +used vs. directly reading @console->flags. + +Refactor and clarify that console_srcu_read_flags() is only +needed if the console is registered or the caller is in a +context where the registration status of the console may change +(due to another context). + +The function requires the caller holds @console_srcu, which will +ensure that the caller sees an appropriate @flags value for the +registered console and that exit/cleanup routines will not run +if the console is in the process of unregistration. + +Signed-off-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + include/linux/console.h | 28 +++++++++++++++++----------- + 1 file changed, 17 insertions(+), 11 deletions(-) + +--- a/include/linux/console.h ++++ b/include/linux/console.h +@@ -446,28 +446,34 @@ extern void console_list_unlock(void) __ + extern struct hlist_head console_list; + + /** +- * console_srcu_read_flags - Locklessly read the console flags ++ * console_srcu_read_flags - Locklessly read flags of a possibly registered ++ * console + * @con: struct console pointer of console to read flags from + * +- * This function provides the necessary READ_ONCE() and data_race() +- * notation for locklessly reading the console flags. The READ_ONCE() +- * in this function matches the WRITE_ONCE() when @flags are modified +- * for registered consoles with console_srcu_write_flags(). ++ * Locklessly reading @con->flags provides a consistent read value because ++ * there is at most one CPU modifying @con->flags and that CPU is using only ++ * read-modify-write operations to do so. + * +- * Only use this function to read console flags when locklessly +- * iterating the console list via srcu. ++ * Requires console_srcu_read_lock to be held, which implies that @con might ++ * be a registered console. The purpose of holding console_srcu_read_lock is ++ * to guarantee that the console state is valid (CON_SUSPENDED/CON_ENABLED) ++ * and that no exit/cleanup routines will run if the console is currently ++ * undergoing unregistration. ++ * ++ * If the caller is holding the console_list_lock or it is _certain_ that ++ * @con is not and will not become registered, the caller may read ++ * @con->flags directly instead. + * + * Context: Any context. ++ * Return: The current value of the @con->flags field. + */ + static inline short console_srcu_read_flags(const struct console *con) + { + WARN_ON_ONCE(!console_srcu_read_lock_is_held()); + + /* +- * Locklessly reading console->flags provides a consistent +- * read value because there is at most one CPU modifying +- * console->flags and that CPU is using only read-modify-write +- * operations to do so. ++ * The READ_ONCE() matches the WRITE_ONCE() when @flags are modified ++ * for registered consoles with console_srcu_write_flags(). + */ + return data_race(READ_ONCE(con->flags)); + } |