Konstantin Demin
c3d09a3e94
imported from https://salsa.debian.org/kernel-team/linux.git commit 9d5cc9d9d6501d7f1dd7e194d4b245bd0b6c6a22 version 6.11.4-1
125 lines
4.3 KiB
Diff
125 lines
4.3 KiB
Diff
From: John Ogness <john.ogness@linutronix.de>
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Date: Tue, 20 Aug 2024 08:35:35 +0206
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Subject: [PATCH 09/54] printk: nbcon: Use driver synchronization while
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(un)registering
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patches-6.11-rt7.tar.xz
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Console drivers typically have to deal with access to the
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hardware via user input/output (such as an interactive login
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shell) and output of kernel messages via printk() calls.
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They use some classic driver-specific locking mechanism in most
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situations. But console->write_atomic() callbacks, used by nbcon
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consoles, are synchronized only by acquiring the console
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context.
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The synchronization via the console context ownership is possible
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only when the console driver is registered. It is when a
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particular device driver is connected with a particular console
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driver.
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The two synchronization mechanisms must be synchronized between
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each other. It is tricky because the console context ownership
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is quite special. It might be taken over by a higher priority
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context. Also CPU migration must be disabled. The most tricky
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part is to (dis)connect these two mechanisms during the console
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(un)registration.
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Use the driver-specific locking callbacks: device_lock(),
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device_unlock(). They allow taking the device-specific lock
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while the device is being (un)registered by the related console
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driver.
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For example, these callbacks lock/unlock the port lock for
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serial port drivers.
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Note that the driver-specific locking is only needed during
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(un)register if it is an nbcon console with the write_atomic()
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callback implemented. If write_atomic() is not implemented, the
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driver should never attempt to access the hardware without
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first acquiring its driver-specific lock.
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Signed-off-by: John Ogness <john.ogness@linutronix.de>
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Reviewed-by: Petr Mladek <pmladek@suse.com>
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Link: https://lore.kernel.org/r/20240820063001.36405-10-john.ogness@linutronix.de
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Signed-off-by: Petr Mladek <pmladek@suse.com>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/printk/printk.c | 33 ++++++++++++++++++++++++++++++++-
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1 file changed, 32 insertions(+), 1 deletion(-)
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -3549,9 +3549,11 @@ static int unregister_console_locked(str
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*/
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void register_console(struct console *newcon)
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{
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- struct console *con;
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+ bool use_device_lock = (newcon->flags & CON_NBCON) && newcon->write_atomic;
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bool bootcon_registered = false;
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bool realcon_registered = false;
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+ struct console *con;
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+ unsigned long flags;
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u64 init_seq;
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int err;
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@@ -3639,6 +3641,19 @@ void register_console(struct console *ne
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}
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/*
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+ * If another context is actively using the hardware of this new
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+ * console, it will not be aware of the nbcon synchronization. This
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+ * is a risk that two contexts could access the hardware
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+ * simultaneously if this new console is used for atomic printing
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+ * and the other context is still using the hardware.
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+ *
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+ * Use the driver synchronization to ensure that the hardware is not
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+ * in use while this new console transitions to being registered.
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+ */
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+ if (use_device_lock)
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+ newcon->device_lock(newcon, &flags);
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+
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+ /*
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* Put this console in the list - keep the
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* preferred driver at the head of the list.
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*/
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@@ -3662,6 +3677,10 @@ void register_console(struct console *ne
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* register_console() completes.
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*/
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+ /* This new console is now registered. */
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+ if (use_device_lock)
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+ newcon->device_unlock(newcon, flags);
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+
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console_sysfs_notify();
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/*
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@@ -3690,6 +3709,8 @@ EXPORT_SYMBOL(register_console);
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/* Must be called under console_list_lock(). */
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static int unregister_console_locked(struct console *console)
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{
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+ bool use_device_lock = (console->flags & CON_NBCON) && console->write_atomic;
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+ unsigned long flags;
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int res;
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lockdep_assert_console_list_lock_held();
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@@ -3708,8 +3729,18 @@ static int unregister_console_locked(str
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if (!console_is_registered_locked(console))
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return -ENODEV;
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+ /*
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+ * Use the driver synchronization to ensure that the hardware is not
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+ * in use while this console transitions to being unregistered.
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+ */
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+ if (use_device_lock)
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+ console->device_lock(console, &flags);
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+
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hlist_del_init_rcu(&console->node);
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+ if (use_device_lock)
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+ console->device_unlock(console, flags);
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+
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/*
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* <HISTORICAL>
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* If this isn't the last console and it has CON_CONSDEV set, we
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