From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk v2 27/38] printk: console_flush_all: use srcu console list iterator
Date: Mon, 7 Nov 2022 14:03:31 +0100 [thread overview]
Message-ID: <Y2kCI7pAiQBNefgi@alley> (raw)
In-Reply-To: <87a6534osd.fsf@jogness.linutronix.de>
On Mon 2022-11-07 01:06:02, John Ogness wrote:
> On 2022-10-25, Petr Mladek <pmladek@suse.com> wrote:
> >> 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
> >>
> >> @@ -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;
> >
> > Please, release the SRCU read lock here:
> >
> > if (*handover) {
> > console_srcu_read_unlock(cookie);
> > return false;
> > }
> >
> > The lock should be released in the same function where it was taken.
> > It does not require passing the cookie and looks more straightforward.
>
> It looks more straight forward, but it is incorrect from a locking
> perspective.
>
> The locking order was:
>
> console_lock()
> console_srcu_read_lock()
>
> But for a handover at this point in code, console_emit_next_record() has
> already released the console_lock (to the spinning context). The
> console_srcu_read_lock should have been released first.
Ah, I see. I should be read all the comments more carefully.
I do not know about any better solution. Feel free to use:
Reviewed-by: Petr Mladek <pmladek@suse.com>
Note:
The complexity is caused by calling
mutex_release() in console_lock_spinning_disable_and_check() and
mutex_acquire() in console_trylock_spinning().
I wondered if we really need to do so. These functions actually do not
release or acquire the console_lock. But it seems that it is necessary
because lockdep is not able to track the lock when it was moved into
another process.
I even tried to replace mutex_acquire()/mutex_release() with
rwsem_acquire()/rwsem_release(). But it did not help. lockdep
still complained when I removed these calls from
the _spinning_() API. Sigh.
Best Regards,
Petr
next prev parent reply other threads:[~2022-11-07 13:03 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 ` [PATCH printk v2 27/38] printk: console_flush_all: " John Ogness
2022-10-25 15:17 ` Petr Mladek
2022-11-07 0:00 ` John Ogness
2022-11-07 13:03 ` Petr Mladek [this message]
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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