[PATCH printk v2 25/38] proc: consoles: document console_lock usage

John Ogness
2022-10-19T15:07:12Z

The console_lock is held throughout the start/show/stop procedure
to print out device/driver information about all registered
consoles. Since the console_lock is being used for multiple reasons,
explicitly document these reasons. This will be useful when the
console_lock is split into fine-grained locking.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
fs/proc/consoles.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/fs/proc/consoles.c b/fs/proc/consoles.c
index cf2e0788f9c7..32512b477605 100644
--- a/fs/proc/consoles.c
+++ b/fs/proc/consoles.c
@@ -63,6 +63,14 @@ static void *c_start(struct seq_file *m, loff_t *pos)
struct console *con;
loff_t off = 0;

+ /*
+ * Stop console printing because the device() callback may
+ * assume the console is not within its write() callback.
+ *
+ * Hold the console_lock to guarantee safe traversal of the
+ * console list. SRCU cannot be used because there is no
+ * place to store the SRCU cookie.
+ */
console_lock();
for_each_console(con)
if (off++ == *pos)
--
2.30.2