diff options
author | John Ogness <john.ogness@linutronix.de> | 2022-11-16 19:21:24 +0300 |
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committer | Petr Mladek <pmladek@suse.com> | 2022-12-02 13:25:00 +0300 |
commit | 100bdef2c198b8dc64df011dc4a2152db913c8ba (patch) | |
tree | 49aa89134c32a85a46b6fb7d38015a12bbb37b38 /include/linux/console.h | |
parent | 4dc64682ad37abb02c54ca598430ac27de60c21a (diff) | |
download | linux-100bdef2c198b8dc64df011dc4a2152db913c8ba.tar.xz |
console: introduce wrappers to read/write console flags
After switching to SRCU for console list iteration, some readers
will begin readings console->flags as a data race. Locklessly
reading console->flags provides a consistent value because there
is at most one CPU modifying console->flags and that CPU is
using only read-modify-write operations.
Introduce a wrapper for SRCU iterators to read console flags.
Introduce a matching wrapper to write to flags of registered
consoles. Writing to flags of registered consoles is synchronized
by the console_list_lock.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-13-john.ogness@linutronix.de
Diffstat (limited to 'include/linux/console.h')
-rw-r--r-- | include/linux/console.h | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/include/linux/console.h b/include/linux/console.h index 24d83e24840b..c1ca461d088a 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -184,6 +184,51 @@ extern void console_list_unlock(void) __releases(console_mutex); extern struct hlist_head console_list; /** + * console_srcu_read_flags - Locklessly read the console flags + * @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(). + * + * Only use this function to read console flags when locklessly + * iterating the console list via srcu. + * + * Context: Any context. + */ +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. + */ + return data_race(READ_ONCE(con->flags)); +} + +/** + * console_srcu_write_flags - Write flags for a registered console + * @con: struct console pointer of console to write flags to + * @flags: new flags value to write + * + * Only use this function to write flags for registered consoles. It + * requires holding the console_list_lock. + * + * Context: Any context. + */ +static inline void console_srcu_write_flags(struct console *con, short flags) +{ + lockdep_assert_console_list_lock_held(); + + /* This matches the READ_ONCE() in console_srcu_read_flags(). */ + WRITE_ONCE(con->flags, flags); +} + +/** * for_each_console_srcu() - Iterator over registered consoles * @con: struct console pointer used as loop cursor * |