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printk: Add per-console suspended state 

Currently the global @console_suspended is used to determine if
consoles are in a suspended state. Its primary purpose is to allow
usage of the console_lock when suspended without causing console
printing. It is synchronized by the console_lock.

Rather than relying on the console_lock to determine suspended
state, make it an official per-console state that is set within
console->flags. This allows the state to be queried via SRCU.

Remove @console_suspended. Console printing will still be avoided
when suspended because console_is_usable() returns false when
the new suspended flag is set for that console.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230717194607.145135-7-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2023-07-17 21:52:06 +02:06 committed by Petr Mladek
parent 696ffaf50e
commit 9e70a5e109
2 changed files with 47 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/console.h
View File

@ -154,6 +154,8 @@ static inline int con_debug_leave(void)
* receiving the printk spam for obvious reasons.
* @CON_EXTENDED: The console supports the extended output format of
* /dev/kmesg which requires a larger output buffer.
* @CON_SUSPENDED: Indicates if a console is suspended. If true, the
* printing callbacks must not be called.
*/
enum cons_flags {
CON_PRINTBUFFER = BIT(0),
@ -163,6 +165,7 @@ enum cons_flags {
CON_ANYTIME = BIT(4),
CON_BRL = BIT(5),
CON_EXTENDED = BIT(6),
CON_SUSPENDED = BIT(7),
};
/**

74
kernel/printk/printk.c
View File

@ -86,7 +86,7 @@ EXPORT_SYMBOL(oops_in_progress);
static DEFINE_MUTEX(console_mutex);
/*
* console_sem protects updates to console->seq and console_suspended,
* console_sem protects updates to console->seq
* and also provides serialization for console printing.
*/
static DEFINE_SEMAPHORE(console_sem);
@ -359,7 +359,7 @@ static bool panic_in_progress(void)
* paths in the console code where we end up in places I want
* locked without the console semaphore held).
*/
static int console_locked, console_suspended;
static int console_locked;
/*
* Array of consoles built from command line options (console=)
@ -2549,22 +2549,46 @@ MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to hig
*/
void suspend_console(void)
{
struct console *con;
if (!console_suspend_enabled)
return;
pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
pr_flush(1000, true);
console_lock();
console_suspended = 1;
up_console_sem();
console_list_lock();
for_each_console(con)
console_srcu_write_flags(con, con->flags | CON_SUSPENDED);
console_list_unlock();
/*
* Ensure that all SRCU list walks have completed. All printing
* contexts must be able to see that they are suspended so that it
* is guaranteed that all printing has stopped when this function
* completes.
*/
synchronize_srcu(&console_srcu);
}
void resume_console(void)
{
struct console *con;
if (!console_suspend_enabled)
return;
down_console_sem();
console_suspended = 0;
console_unlock();
console_list_lock();
for_each_console(con)
console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);
console_list_unlock();
/*
* Ensure that all SRCU list walks have completed. All printing
* contexts must be able to see they are no longer suspended so
* that they are guaranteed to wake up and resume printing.
*/
synchronize_srcu(&console_srcu);
pr_flush(1000, true);
}
@ -2623,8 +2647,6 @@ void console_lock(void)
msleep(1000);
down_console_sem();
if (console_suspended)
return;
console_locked = 1;
console_may_schedule = 1;
}
@ -2645,10 +2667,6 @@ int console_trylock(void)
return 0;
if (down_trylock_console_sem())
return 0;
if (console_suspended) {
up_console_sem();
return 0;
}
console_locked = 1;
console_may_schedule = 0;
return 1;
@ -2674,6 +2692,9 @@ static inline bool console_is_usable(struct console *con)
if (!(flags & CON_ENABLED))
return false;
if ((flags & CON_SUSPENDED))
return false;
if (!con->write)
return false;
@ -2992,11 +3013,6 @@ void console_unlock(void)
bool flushed;
u64 next_seq;
if (console_suspended) {
up_console_sem();
return;
}
/*
* Console drivers are called with interrupts disabled, so
* @console_may_schedule should be cleared before; however, we may
@ -3726,8 +3742,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
/*
* Hold the console_lock to guarantee safe access to
* console->seq and to prevent changes to @console_suspended
* until all consoles have been processed.
* console->seq.
*/
console_lock();
@ -3735,6 +3750,11 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
for_each_console_srcu(c) {
if (con && con != c)
continue;
/*
* If consoles are not usable, it cannot be expected
* that they make forward progress, so only increment
* @diff for usable consoles.
*/
if (!console_is_usable(c))
continue;
printk_seq = c->seq;
@ -3743,18 +3763,12 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
}
console_srcu_read_unlock(cookie);
/*
* If consoles are suspended, it cannot be expected that they
* make forward progress, so timeout immediately. @diff is
* still used to return a valid flush status.
*/
if (console_suspended)
remaining = 0;
else if (diff != last_diff && reset_on_progress)
if (diff != last_diff && reset_on_progress)
remaining = timeout_ms;
console_unlock();
/* Note: @diff is 0 if there are no usable consoles. */
if (diff == 0 || remaining == 0)
break;
@ -3788,7 +3802,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
* printer has been seen to make some forward progress.
*
* Context: Process context. May sleep while acquiring console lock.
* Return: true if all enabled printers are caught up.
* Return: true if all usable printers are caught up.
*/
static bool pr_flush(int timeout_ms, bool reset_on_progress)
{