From: John Ogness <john.ogness@linutronix.de> To: Petr Mladek <pmladek@suse.com> Cc: Juergen Gross <jgross@suse.com>, linux-fbdev@vger.kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Helge Deller <deller@gmx.de>, linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>, Javier Martinez Canillas <javierm@redhat.com>, Sergey Senozhatsky <senozhatsky@chromium.org>, dri-devel@lists.freedesktop.org, Thomas Zimmermann <tzimmermann@suse.de>, Tom Rix <trix@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Boris Ostrovsky <boris.ostrovsky@oracle.com> Subject: [PATCH printk v4 31/39] printk, xen: fbfront: create/use safe function for forcing preferred Date: Mon, 14 Nov 2022 17:35:24 +0106 [thread overview] Message-ID: <20221114162932.141883-32-john.ogness@linutronix.de> (raw) In-Reply-To: <20221114162932.141883-1-john.ogness@linutronix.de> With commit 9e124fe16ff2("xen: Enable console tty by default in domU if it's not a dummy") a hack was implemented to make sure that the tty console remains the console behind the /dev/console device. The main problem with the hack is that, after getting the console pointer to the tty console, it is assumed the pointer is still valid after releasing the console_sem. This assumption is incorrect and unsafe. Make the hack safe by introducing a new function console_force_preferred_locked() and perform the full operation under the console_list_lock. Signed-off-by: John Ogness <john.ogness@linutronix.de> --- drivers/video/fbdev/xen-fbfront.c | 12 +++----- include/linux/console.h | 1 + kernel/printk/printk.c | 49 +++++++++++++++++++++++++++++-- 3 files changed, 51 insertions(+), 11 deletions(-) diff --git a/drivers/video/fbdev/xen-fbfront.c b/drivers/video/fbdev/xen-fbfront.c index 4d2694d904aa..8752d389e382 100644 --- a/drivers/video/fbdev/xen-fbfront.c +++ b/drivers/video/fbdev/xen-fbfront.c @@ -504,18 +504,14 @@ static void xenfb_make_preferred_console(void) if (console_set_on_cmdline) return; - console_lock(); + console_list_lock(); for_each_console(c) { if (!strcmp(c->name, "tty") && c->index == 0) break; } - console_unlock(); - if (c) { - unregister_console(c); - c->flags |= CON_CONSDEV; - c->flags &= ~CON_PRINTBUFFER; /* don't print again */ - register_console(c); - } + if (c) + console_force_preferred_locked(c); + console_list_unlock(); } static int xenfb_resume(struct xenbus_device *dev) diff --git a/include/linux/console.h b/include/linux/console.h index f716e1dd9eaf..9cea254b34b8 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -291,6 +291,7 @@ enum con_flush_mode { }; extern int add_preferred_console(char *name, int idx, char *options); +extern void console_force_preferred_locked(struct console *con); extern void register_console(struct console *); extern int unregister_console(struct console *); extern void console_lock(void); diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index e770b1ede6c9..dff76c1cef80 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -247,9 +247,10 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write, void console_list_lock(void) { /* - * In unregister_console(), synchronize_srcu() is called with the - * console_list_lock held. Therefore it is not allowed that the - * console_list_lock is taken with the srcu_lock held. + * In unregister_console() and console_force_preferred_locked(), + * synchronize_srcu() is called with the console_list_lock held. + * Therefore it is not allowed that the console_list_lock is taken + * with the srcu_lock held. * * Detecting if this context is really in the read-side critical * section is only possible if the appropriate debug options are @@ -3461,6 +3462,48 @@ int unregister_console(struct console *console) } EXPORT_SYMBOL(unregister_console); +/** + * console_force_preferred_locked - force a registered console preferred + * @con: The registered console to force preferred. + * + * Must be called under console_list_lock(). + */ +void console_force_preferred_locked(struct console *con) +{ + struct console *cur_pref_con; + + if (!console_is_registered_locked(con)) + return; + + cur_pref_con = console_first(); + + /* Already preferred? */ + if (cur_pref_con == con) + return; + + /* + * Delete, but do not re-initialize the entry. This allows the console + * to continue to appear registered (via any hlist_unhashed_lockless() + * checks), even though it was briefly removed from the console list. + */ + hlist_del_rcu(&con->node); + + /* + * Ensure that all SRCU list walks have completed so that the console + * can be added to the beginning of the console list and its forward + * list pointer can be re-initialized. + */ + synchronize_srcu(&console_srcu); + + con->flags |= CON_CONSDEV; + WARN_ON(!con->device); + + /* Only the new head can have CON_CONSDEV set. */ + console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV); + hlist_add_behind_rcu(&con->node, console_list.first); +} +EXPORT_SYMBOL(console_force_preferred_locked); + /* * Initialize the console device. This is called *early*, so * we can't necessarily depend on lots of kernel help here. -- 2.30.2
WARNING: multiple messages have this Message-ID (diff)
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, Helge Deller <deller@gmx.de>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Javier Martinez Canillas <javierm@redhat.com>, Thomas Zimmermann <tzimmermann@suse.de>, Juergen Gross <jgross@suse.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Tom Rix <trix@redhat.com>, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: [PATCH printk v4 31/39] printk, xen: fbfront: create/use safe function for forcing preferred Date: Mon, 14 Nov 2022 17:35:24 +0106 [thread overview] Message-ID: <20221114162932.141883-32-john.ogness@linutronix.de> (raw) In-Reply-To: <20221114162932.141883-1-john.ogness@linutronix.de> With commit 9e124fe16ff2("xen: Enable console tty by default in domU if it's not a dummy") a hack was implemented to make sure that the tty console remains the console behind the /dev/console device. The main problem with the hack is that, after getting the console pointer to the tty console, it is assumed the pointer is still valid after releasing the console_sem. This assumption is incorrect and unsafe. Make the hack safe by introducing a new function console_force_preferred_locked() and perform the full operation under the console_list_lock. Signed-off-by: John Ogness <john.ogness@linutronix.de> --- drivers/video/fbdev/xen-fbfront.c | 12 +++----- include/linux/console.h | 1 + kernel/printk/printk.c | 49 +++++++++++++++++++++++++++++-- 3 files changed, 51 insertions(+), 11 deletions(-) diff --git a/drivers/video/fbdev/xen-fbfront.c b/drivers/video/fbdev/xen-fbfront.c index 4d2694d904aa..8752d389e382 100644 --- a/drivers/video/fbdev/xen-fbfront.c +++ b/drivers/video/fbdev/xen-fbfront.c @@ -504,18 +504,14 @@ static void xenfb_make_preferred_console(void) if (console_set_on_cmdline) return; - console_lock(); + console_list_lock(); for_each_console(c) { if (!strcmp(c->name, "tty") && c->index == 0) break; } - console_unlock(); - if (c) { - unregister_console(c); - c->flags |= CON_CONSDEV; - c->flags &= ~CON_PRINTBUFFER; /* don't print again */ - register_console(c); - } + if (c) + console_force_preferred_locked(c); + console_list_unlock(); } static int xenfb_resume(struct xenbus_device *dev) diff --git a/include/linux/console.h b/include/linux/console.h index f716e1dd9eaf..9cea254b34b8 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -291,6 +291,7 @@ enum con_flush_mode { }; extern int add_preferred_console(char *name, int idx, char *options); +extern void console_force_preferred_locked(struct console *con); extern void register_console(struct console *); extern int unregister_console(struct console *); extern void console_lock(void); diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index e770b1ede6c9..dff76c1cef80 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -247,9 +247,10 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write, void console_list_lock(void) { /* - * In unregister_console(), synchronize_srcu() is called with the - * console_list_lock held. Therefore it is not allowed that the - * console_list_lock is taken with the srcu_lock held. + * In unregister_console() and console_force_preferred_locked(), + * synchronize_srcu() is called with the console_list_lock held. + * Therefore it is not allowed that the console_list_lock is taken + * with the srcu_lock held. * * Detecting if this context is really in the read-side critical * section is only possible if the appropriate debug options are @@ -3461,6 +3462,48 @@ int unregister_console(struct console *console) } EXPORT_SYMBOL(unregister_console); +/** + * console_force_preferred_locked - force a registered console preferred + * @con: The registered console to force preferred. + * + * Must be called under console_list_lock(). + */ +void console_force_preferred_locked(struct console *con) +{ + struct console *cur_pref_con; + + if (!console_is_registered_locked(con)) + return; + + cur_pref_con = console_first(); + + /* Already preferred? */ + if (cur_pref_con == con) + return; + + /* + * Delete, but do not re-initialize the entry. This allows the console + * to continue to appear registered (via any hlist_unhashed_lockless() + * checks), even though it was briefly removed from the console list. + */ + hlist_del_rcu(&con->node); + + /* + * Ensure that all SRCU list walks have completed so that the console + * can be added to the beginning of the console list and its forward + * list pointer can be re-initialized. + */ + synchronize_srcu(&console_srcu); + + con->flags |= CON_CONSDEV; + WARN_ON(!con->device); + + /* Only the new head can have CON_CONSDEV set. */ + console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV); + hlist_add_behind_rcu(&con->node, console_list.first); +} +EXPORT_SYMBOL(console_force_preferred_locked); + /* * Initialize the console device. This is called *early*, so * we can't necessarily depend on lots of kernel help here. -- 2.30.2
next prev parent reply other threads:[~2022-11-14 16:29 UTC|newest] Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-11-14 16:28 [PATCH printk v4 00/39] reduce console_lock scope John Ogness 2022-11-14 16:28 ` John Ogness 2022-11-14 16:28 ` John Ogness 2022-11-14 16:28 ` John Ogness 2022-11-14 16:28 ` [PATCH printk v4 01/39] serial: kgdboc: Lock console list in probe function John Ogness 2022-11-14 16:28 ` [PATCH printk v4 02/39] printk: Convert console_drivers list to hlist John Ogness 2022-11-14 16:28 ` [PATCH printk v4 03/39] printk: Prepare for SRCU console list protection John Ogness 2022-11-15 10:50 ` Petr Mladek 2022-11-15 11:33 ` John Ogness 2022-11-15 12:03 ` Petr Mladek 2022-11-14 16:28 ` [PATCH printk v4 04/39] printk: register_console: use "registered" for variable names John Ogness 2022-11-15 11:01 ` Petr Mladek 2022-11-14 16:28 ` [PATCH printk v4 05/39] printk: fix setting first seq for consoles John Ogness 2022-11-15 12:04 ` Petr Mladek 2022-11-14 16:28 ` [PATCH printk v4 06/39] um: kmsg_dump: only dump when no output console available John Ogness 2022-11-14 16:28 ` John Ogness 2022-11-14 16:29 ` [PATCH printk v4 07/39] tty: serial: kgdboc: document console_lock usage John Ogness 2022-11-14 16:29 ` [PATCH printk v4 08/39] tty: tty_io: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 09/39] proc: consoles: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 10/39] printk: introduce console_list_lock John Ogness 2022-11-14 16:29 ` [PATCH printk v4 11/39] console: introduce wrappers to read/write console flags John Ogness 2022-11-15 12:26 ` Petr Mladek 2022-11-14 16:29 ` [PATCH printk v4 12/39] um: kmsg_dumper: use srcu console list iterator John Ogness 2022-11-14 16:29 ` John Ogness 2022-11-14 16:29 ` [PATCH printk v4 13/39] kdb: " John Ogness 2022-11-14 21:16 ` Aaron Tomlin 2022-11-14 16:29 ` [PATCH printk v4 14/39] printk: console_flush_all: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 15/39] printk: __pr_flush: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 16/39] printk: console_is_usable: use console_srcu_read_flags John Ogness 2022-11-15 12:47 ` Petr Mladek 2022-11-14 16:29 ` [PATCH printk v4 17/39] printk: console_unblank: use srcu console list iterator John Ogness 2022-11-14 16:29 ` [PATCH printk v4 18/39] printk: console_flush_on_panic: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 19/39] printk: console_device: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 20/39] console: introduce console_is_registered() John Ogness 2022-11-14 16:29 ` [PATCH printk v4 21/39] serial_core: replace uart_console_enabled() with uart_console_registered() John Ogness 2022-11-14 16:29 ` [PATCH printk v4 22/39] tty: nfcon: use console_is_registered() John Ogness 2022-11-15 13:08 ` Petr Mladek 2022-11-14 16:29 ` [PATCH printk v4 23/39] efi: earlycon: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 24/39] tty: hvc: " John Ogness 2022-11-14 16:29 ` John Ogness 2022-11-14 16:29 ` [PATCH printk v4 25/39] tty: serial: earlycon: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 26/39] tty: serial: pic32_uart: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 27/39] tty: serial: samsung_tty: " John Ogness 2022-11-14 16:29 ` John Ogness 2022-11-14 16:29 ` [PATCH printk v4 28/39] tty: serial: xilinx_uartps: " John Ogness 2022-11-14 16:29 ` John Ogness 2022-11-14 16:29 ` [PATCH printk v4 29/39] usb: early: xhci-dbc: " John Ogness 2022-11-14 16:29 ` [PATCH printk v4 30/39] netconsole: avoid CON_ENABLED misuse to track registration John Ogness 2022-11-14 16:29 ` John Ogness [this message] 2022-11-14 16:29 ` [PATCH printk v4 31/39] printk, xen: fbfront: create/use safe function for forcing preferred John Ogness 2022-11-14 19:51 ` John Ogness 2022-11-14 19:51 ` John Ogness 2022-11-15 13:22 ` Petr Mladek 2022-11-15 13:22 ` Petr Mladek 2022-11-14 16:29 ` [PATCH printk v4 32/39] tty: tty_io: use console_list_lock for list synchronization John Ogness 2022-11-14 16:29 ` [PATCH printk v4 33/39] proc: consoles: use console_list_lock for list iteration John Ogness 2022-11-14 16:29 ` [PATCH printk v4 34/39] tty: serial: kgdboc: use srcu console list iterator John Ogness 2022-11-15 15:17 ` Petr Mladek 2022-11-14 16:29 ` [PATCH printk v4 35/39] tty: serial: kgdboc: use console_list_lock for list traversal John Ogness 2022-11-15 15:18 ` Petr Mladek 2022-11-14 16:29 ` [PATCH printk v4 36/39] tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console() John Ogness 2022-11-14 16:29 ` [PATCH printk v4 37/39] tty: serial: kgdboc: use console_list_lock to trap exit John Ogness 2022-11-14 16:29 ` [PATCH printk v4 38/39] printk: relieve console_lock of list synchronization duties John Ogness 2022-11-15 15:34 ` replay log: " Petr Mladek 2022-11-15 16:41 ` John Ogness 2022-11-15 18:23 ` Petr Mladek 2022-11-16 8:52 ` John Ogness 2022-11-16 8:56 ` John Ogness 2022-11-16 9:08 ` John Ogness 2022-11-16 9:48 ` Petr Mladek 2022-11-15 16:41 ` Petr Mladek 2022-11-15 17:15 ` John Ogness 2022-11-15 18:36 ` Petr Mladek 2022-11-14 16:29 ` [PATCH printk v4 39/39] tty: serial: sh-sci: use setup() callback for early console John Ogness 2022-11-15 16:43 ` Petr Mladek
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