From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: [PATCH printk v2 27/38] printk: console_flush_all: use srcu console list iterator
Date: Wed, 19 Oct 2022 17:01:49 +0206 [thread overview]
Message-ID: <20221019145600.1282823-28-john.ogness@linutronix.de> (raw)
In-Reply-To: <20221019145600.1282823-1-john.ogness@linutronix.de>
Guarantee safe iteration of the console list by using SRCU.
Note that in the case of a handover, the SRCU read lock is also
released. This is documented in the function description and as
comments in the code. It is a bit tricky, but this preserves the
lockdep lock ordering for the context handing over the
console_lock:
console_lock()
| mutex_acquire(&console_lock_dep_map) <-- console lock
|
console_unlock()
| console_flush_all()
| | srcu_read_lock(&console_srcu) <-- srcu lock
| | console_emit_next_record()
| | | console_lock_spinning_disable_and_check()
| | | | srcu_read_unlock(&console_srcu) <-- srcu unlock
| | | | mutex_release(&console_lock_dep_map) <-- console unlock
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/printk.c | 38 ++++++++++++++++++++++++++++----------
1 file changed, 28 insertions(+), 10 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7ff2fc75fc3b..c4d5d58b5977 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1851,7 +1851,7 @@ static void console_lock_spinning_enable(void)
*
* Return: 1 if the lock rights were passed, 0 otherwise.
*/
-static int console_lock_spinning_disable_and_check(void)
+static int console_lock_spinning_disable_and_check(int cookie)
{
int waiter;
@@ -1870,6 +1870,12 @@ static int console_lock_spinning_disable_and_check(void)
spin_release(&console_owner_dep_map, _THIS_IP_);
+ /*
+ * Preserve lockdep lock ordering. Release the SRCU read lock before
+ * releasing the console_lock.
+ */
+ console_srcu_read_unlock(cookie);
+
/*
* Hand off console_lock to waiter. The waiter will perform
* the up(). After this, the waiter is the console_lock owner.
@@ -2353,7 +2359,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
char *text, size_t text_len,
struct dev_printk_info *dev_info) { return 0; }
static void console_lock_spinning_enable(void) { }
-static int console_lock_spinning_disable_and_check(void) { return 0; }
+static int console_lock_spinning_disable_and_check(int cookie) { return 0; }
static void call_console_driver(struct console *con, const char *text, size_t len,
char *dropped_text)
{
@@ -2695,8 +2701,8 @@ static void __console_unlock(void)
* DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL.
*
* @handover will be set to true if a printk waiter has taken over the
- * console_lock, in which case the caller is no longer holding the
- * console_lock. Otherwise it is set to false.
+ * console_lock, in which case the caller is no longer holding both the
+ * console_lock and the SRCU read lock. Otherwise it is set to false.
*
* Returns false if the given console has no next record to print, otherwise
* true.
@@ -2704,7 +2710,7 @@ static void __console_unlock(void)
* Requires the console_lock.
*/
static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
- char *dropped_text, bool *handover)
+ char *dropped_text, bool *handover, int cookie)
{
static int panic_console_dropped;
struct printk_info info;
@@ -2764,7 +2770,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_
con->seq++;
- *handover = console_lock_spinning_disable_and_check();
+ *handover = console_lock_spinning_disable_and_check(cookie);
printk_safe_exit_irqrestore(flags);
skip:
return true;
@@ -2801,6 +2807,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
bool any_usable = false;
struct console *con;
bool any_progress;
+ int cookie;
*next_seq = 0;
*handover = false;
@@ -2808,7 +2815,8 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
do {
any_progress = false;
- for_each_console(con) {
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(con) {
bool progress;
if (!console_is_usable(con))
@@ -2819,12 +2827,17 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
/* Extended consoles do not print "dropped messages". */
progress = console_emit_next_record(con, &text[0],
&ext_text[0], NULL,
- handover);
+ handover, cookie);
} else {
progress = console_emit_next_record(con, &text[0],
NULL, &dropped_text[0],
- handover);
+ handover, cookie);
}
+
+ /*
+ * If a handover has occurred, the SRCU read lock
+ * is already released.
+ */
if (*handover)
return false;
@@ -2838,14 +2851,19 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
/* Allow panic_cpu to take over the consoles safely. */
if (abandon_console_lock_in_panic())
- return false;
+ goto abandon;
if (do_cond_resched)
cond_resched();
}
+ console_srcu_read_unlock(cookie);
} while (any_progress);
return any_usable;
+
+abandon:
+ console_srcu_read_unlock(cookie);
+ return false;
}
/**
--
2.30.2
next prev parent reply other threads:[~2022-10-19 15:07 UTC|newest]
Thread overview: 129+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-19 14:55 [PATCH printk v2 00/38] reduce console_lock scope John Ogness
2022-10-19 14:55 ` [PATCH printk v2 01/38] serial: kgdboc: Lock console list in probe function John Ogness
2022-10-19 15:41 ` Greg Kroah-Hartman
2022-10-24 5:22 ` Sergey Senozhatsky
2022-10-25 0:34 ` Doug Anderson
2022-10-19 14:55 ` [PATCH printk v2 02/38] printk: Convert console_drivers list to hlist John Ogness
2022-10-19 15:44 ` Greg Kroah-Hartman
2022-10-19 21:46 ` John Ogness
2022-10-20 7:43 ` Greg Kroah-Hartman
2022-10-20 12:36 ` Petr Mladek
2022-10-24 5:23 ` Sergey Senozhatsky
2022-10-19 14:55 ` [PATCH printk v2 03/38] printk: Prepare for SRCU console list protection John Ogness
2022-10-19 15:16 ` Miguel Ojeda
2022-10-19 17:12 ` Paul E. McKenney
2022-10-21 8:34 ` Petr Mladek
2022-10-31 13:06 ` John Ogness
2022-10-31 14:09 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 04/38] printk: introduce console_is_enabled() wrapper John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 8:57 ` Petr Mladek
2022-10-21 9:37 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 05/38] printk: use console_is_enabled() John Ogness
2022-10-21 9:25 ` Petr Mladek
2022-10-31 15:39 ` John Ogness
2022-10-19 14:55 ` [PATCH printk v2 06/38] tty: nfcon: " John Ogness
2022-10-21 9:55 ` Petr Mladek
2022-10-31 15:59 ` John Ogness
2022-11-01 8:57 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 07/38] um: kmsg_dump: " John Ogness
2022-10-21 12:46 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 08/38] efi: earlycon: " John Ogness
2022-10-19 15:32 ` Ard Biesheuvel
2022-10-21 12:53 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 09/38] netconsole: " John Ogness
2022-10-21 13:14 ` Petr Mladek
2022-11-04 15:12 ` John Ogness
2022-10-19 14:55 ` [PATCH printk v2 10/38] tty: hvc: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 13:22 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 11/38] tty: serial: earlycon: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 13:51 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 12/38] tty: serial: kgdboc: " John Ogness
2022-10-19 16:00 ` Greg Kroah-Hartman
2022-10-21 14:10 ` Petr Mladek
2022-10-24 22:46 ` Doug Anderson
2022-10-25 0:49 ` Doug Anderson
2022-10-25 11:28 ` John Ogness
2022-11-04 16:23 ` John Ogness
2022-11-07 8:47 ` Petr Mladek
2022-11-07 9:45 ` John Ogness
2022-10-19 14:55 ` [PATCH printk v2 13/38] tty: serial: pic32_uart: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 14:11 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 14/38] tty: serial: samsung_tty: " John Ogness
2022-10-19 16:00 ` Greg Kroah-Hartman
2022-10-21 14:14 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 15/38] tty: serial: serial_core: " John Ogness
2022-10-19 16:00 ` Greg Kroah-Hartman
2022-10-21 14:14 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 16/38] tty: serial: xilinx_uartps: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 14:23 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 17/38] tty: tty_io: " John Ogness
2022-10-19 16:00 ` Greg Kroah-Hartman
2022-10-21 14:24 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 18/38] usb: early: xhci-dbc: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 14:27 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 19/38] kdb: kdb_io: " John Ogness
2022-10-21 14:28 ` Petr Mladek
2022-10-25 0:34 ` Doug Anderson
2022-10-19 14:55 ` [PATCH printk v2 20/38] um: kmsg_dumper: use srcu console list iterator John Ogness
2022-10-21 14:56 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 21/38] serial: kgdboc: " John Ogness
2022-10-19 16:02 ` Greg Kroah-Hartman
2022-10-21 15:09 ` Petr Mladek
2022-10-25 0:33 ` Doug Anderson
2022-10-19 14:55 ` [PATCH printk v2 22/38] serial: kgdboc: document console_lock usage John Ogness
2022-10-20 7:42 ` Greg Kroah-Hartman
2022-10-25 0:36 ` Doug Anderson
2022-10-25 10:09 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 23/38] tty: tty_io: " John Ogness
2022-10-20 7:43 ` Greg Kroah-Hartman
2022-10-25 13:31 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 24/38] xen: fbfront: use srcu console list iterator John Ogness
2022-10-25 13:39 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 25/38] proc: consoles: document console_lock usage John Ogness
2022-10-25 14:40 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 26/38] kdb: use srcu console list iterator John Ogness
2022-10-25 0:47 ` Doug Anderson
2022-10-25 14:59 ` Petr Mladek
2022-10-19 14:55 ` John Ogness [this message]
2022-10-25 15:17 ` [PATCH printk v2 27/38] printk: console_flush_all: " Petr Mladek
2022-11-07 0:00 ` John Ogness
2022-11-07 13:03 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 28/38] printk: console_unblank: " John Ogness
2022-10-25 15:28 ` Petr Mladek
2022-10-25 15:31 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 29/38] printk: console_flush_on_panic: " John Ogness
2022-10-25 15:32 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 30/38] printk: console_device: " John Ogness
2022-10-25 15:35 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 31/38] printk: register_console: " John Ogness
2022-10-26 8:20 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 32/38] printk: __pr_flush: " John Ogness
2022-10-26 8:33 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 33/38] printk: introduce console_list_lock John Ogness
2022-10-20 7:53 ` Greg Kroah-Hartman
2022-10-27 10:09 ` Petr Mladek
2022-10-27 18:50 ` Paul E. McKenney
2022-10-28 18:09 ` Boqun Feng
2022-10-28 18:42 ` Paul E. McKenney
2022-11-07 10:10 ` John Ogness
2022-11-07 16:16 ` Paul E. McKenney
2022-10-19 14:55 ` [PATCH printk v2 34/38] serial: kgdboc: use console_list_lock instead of console_lock John Ogness
2022-10-20 7:52 ` Greg Kroah-Hartman
2022-10-27 10:13 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 35/38] tty: tty_io: use console_list_lock for list synchronization John Ogness
2022-10-20 7:43 ` Greg Kroah-Hartman
2022-10-27 10:17 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 36/38] proc: consoles: use console_list_lock for list iteration John Ogness
2022-10-27 12:02 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 37/38] printk: relieve console_lock of list synchronization duties John Ogness
2022-10-27 12:40 ` Petr Mladek
2022-10-19 14:56 ` [PATCH printk v2 38/38] printk, xen: fbfront: create/use safe function for forcing preferred John Ogness
2022-10-27 13:18 ` Petr Mladek
2022-10-27 13:35 ` John Ogness
2022-10-27 14:27 ` Petr Mladek
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