From: John Ogness Date: Tue, 12 Feb 2019 15:29:58 +0100 Subject: [PATCH 20/25] serial: 8250: implement write_atomic Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.2/older/patches-5.2.9-rt3.tar.xz Implement a non-sleeping NMI-safe write_atomic console function in order to support emergency printk messages. Since interrupts need to be disabled during transmit, all usage of the IER register was wrapped with access functions that use the console_atomic_lock function to synchronize register access while tracking the state of the interrupts. This was necessary because write_atomic is can be calling from an NMI context that has preempted write_atomic. Signed-off-by: John Ogness Signed-off-by: Sebastian Andrzej Siewior --- drivers/tty/serial/8250/8250.h | 4 drivers/tty/serial/8250/8250_core.c | 19 +++- drivers/tty/serial/8250/8250_dma.c | 5 - drivers/tty/serial/8250/8250_port.c | 154 ++++++++++++++++++++++++++---------- include/linux/serial_8250.h | 5 + 5 files changed, 139 insertions(+), 48 deletions(-) --- a/drivers/tty/serial/8250/8250.h +++ b/drivers/tty/serial/8250/8250.h @@ -255,3 +255,7 @@ static inline int serial_index(struct ua { return port->minor - 64; } + +void set_ier(struct uart_8250_port *up, unsigned char ier); +void clear_ier(struct uart_8250_port *up); +void restore_ier(struct uart_8250_port *up); --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -265,7 +265,7 @@ static void serial8250_timeout(struct ti static void serial8250_backup_timeout(struct timer_list *t) { struct uart_8250_port *up = from_timer(up, t, timer); - unsigned int iir, ier = 0, lsr; + unsigned int iir, lsr; unsigned long flags; spin_lock_irqsave(&up->port.lock, flags); @@ -274,10 +274,8 @@ static void serial8250_backup_timeout(st * Must disable interrupts or else we risk racing with the interrupt * based handler. */ - if (up->port.irq) { - ier = serial_in(up, UART_IER); - serial_out(up, UART_IER, 0); - } + if (up->port.irq) + clear_ier(up); iir = serial_in(up, UART_IIR); @@ -300,7 +298,7 @@ static void serial8250_backup_timeout(st serial8250_tx_chars(up); if (up->port.irq) - serial_out(up, UART_IER, ier); + restore_ier(up); spin_unlock_irqrestore(&up->port.lock, flags); @@ -578,6 +576,14 @@ serial8250_register_ports(struct uart_dr #ifdef CONFIG_SERIAL_8250_CONSOLE +static void univ8250_console_write_atomic(struct console *co, const char *s, + unsigned int count) +{ + struct uart_8250_port *up = &serial8250_ports[co->index]; + + serial8250_console_write_atomic(up, s, count); +} + static void univ8250_console_write(struct console *co, const char *s, unsigned int count) { @@ -663,6 +669,7 @@ static int univ8250_console_match(struct static struct console univ8250_console = { .name = "ttyS", + .write_atomic = univ8250_console_write_atomic, .write = univ8250_console_write, .device = uart_console_device, .setup = univ8250_console_setup, --- a/drivers/tty/serial/8250/8250_dma.c +++ b/drivers/tty/serial/8250/8250_dma.c @@ -36,7 +36,7 @@ static void __dma_tx_complete(void *para ret = serial8250_tx_dma(p); if (ret) { p->ier |= UART_IER_THRI; - serial_port_out(&p->port, UART_IER, p->ier); + set_ier(p, p->ier); } spin_unlock_irqrestore(&p->port.lock, flags); @@ -101,8 +101,7 @@ int serial8250_tx_dma(struct uart_8250_p if (dma->tx_err) { dma->tx_err = 0; if (p->ier & UART_IER_THRI) { - p->ier &= ~UART_IER_THRI; - serial_out(p, UART_IER, p->ier); + set_ier(p, p->ier); } } return 0; --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -731,7 +731,7 @@ static void serial8250_set_sleep(struct serial_out(p, UART_EFR, UART_EFR_ECB); serial_out(p, UART_LCR, 0); } - serial_out(p, UART_IER, sleep ? UART_IERX_SLEEP : 0); + set_ier(p, sleep ? UART_IERX_SLEEP : 0); if (p->capabilities & UART_CAP_EFR) { serial_out(p, UART_LCR, UART_LCR_CONF_MODE_B); serial_out(p, UART_EFR, efr); @@ -1433,7 +1433,7 @@ static void serial8250_stop_rx(struct ua up->ier &= ~(UART_IER_RLSI | UART_IER_RDI); up->port.read_status_mask &= ~UART_LSR_DR; - serial_port_out(port, UART_IER, up->ier); + set_ier(up, up->ier); serial8250_rpm_put(up); } @@ -1451,7 +1451,7 @@ static void __do_stop_tx_rs485(struct ua serial8250_clear_and_reinit_fifos(p); p->ier |= UART_IER_RLSI | UART_IER_RDI; - serial_port_out(&p->port, UART_IER, p->ier); + set_ier(p, p->ier); } } static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t) @@ -1504,7 +1504,7 @@ static inline void __do_stop_tx(struct u { if (p->ier & UART_IER_THRI) { p->ier &= ~UART_IER_THRI; - serial_out(p, UART_IER, p->ier); + set_ier(p, p->ier); serial8250_rpm_put_tx(p); } } @@ -1557,7 +1557,7 @@ static inline void __start_tx(struct uar if (!(up->ier & UART_IER_THRI)) { up->ier |= UART_IER_THRI; - serial_port_out(port, UART_IER, up->ier); + set_ier(up, up->ier); if (up->bugs & UART_BUG_TXEN) { unsigned char lsr; @@ -1663,7 +1663,7 @@ static void serial8250_disable_ms(struct return; up->ier &= ~UART_IER_MSI; - serial_port_out(port, UART_IER, up->ier); + set_ier(up, up->ier); } static void serial8250_enable_ms(struct uart_port *port) @@ -1677,7 +1677,7 @@ static void serial8250_enable_ms(struct up->ier |= UART_IER_MSI; serial8250_rpm_get(up); - serial_port_out(port, UART_IER, up->ier); + set_ier(up, up->ier); serial8250_rpm_put(up); } @@ -2050,6 +2050,52 @@ static void wait_for_xmitr(struct uart_8 } } +static atomic_t ier_counter = ATOMIC_INIT(0); +static atomic_t ier_value = ATOMIC_INIT(0); + +void set_ier(struct uart_8250_port *up, unsigned char ier) +{ + struct uart_port *port = &up->port; + unsigned int flags; + + console_atomic_lock(&flags); + if (atomic_read(&ier_counter) > 0) + atomic_set(&ier_value, ier); + else + serial_port_out(port, UART_IER, ier); + console_atomic_unlock(flags); +} + +void clear_ier(struct uart_8250_port *up) +{ + struct uart_port *port = &up->port; + unsigned int ier_cleared = 0; + unsigned int flags; + unsigned int ier; + + console_atomic_lock(&flags); + atomic_inc(&ier_counter); + ier = serial_port_in(port, UART_IER); + if (up->capabilities & UART_CAP_UUE) + ier_cleared = UART_IER_UUE; + if (ier != ier_cleared) { + serial_port_out(port, UART_IER, ier_cleared); + atomic_set(&ier_value, ier); + } + console_atomic_unlock(flags); +} + +void restore_ier(struct uart_8250_port *up) +{ + struct uart_port *port = &up->port; + unsigned int flags; + + console_atomic_lock(&flags); + if (atomic_fetch_dec(&ier_counter) == 1) + serial_port_out(port, UART_IER, atomic_read(&ier_value)); + console_atomic_unlock(flags); +} + #ifdef CONFIG_CONSOLE_POLL /* * Console polling routines for writing and reading from the uart while @@ -2081,18 +2127,10 @@ static int serial8250_get_poll_char(stru static void serial8250_put_poll_char(struct uart_port *port, unsigned char c) { - unsigned int ier; struct uart_8250_port *up = up_to_u8250p(port); serial8250_rpm_get(up); - /* - * First save the IER then disable the interrupts - */ - ier = serial_port_in(port, UART_IER); - if (up->capabilities & UART_CAP_UUE) - serial_port_out(port, UART_IER, UART_IER_UUE); - else - serial_port_out(port, UART_IER, 0); + clear_ier(up); wait_for_xmitr(up, BOTH_EMPTY); /* @@ -2105,7 +2143,7 @@ static void serial8250_put_poll_char(str * and restore the IER */ wait_for_xmitr(up, BOTH_EMPTY); - serial_port_out(port, UART_IER, ier); + restore_ier(up); serial8250_rpm_put(up); } @@ -2417,7 +2455,7 @@ void serial8250_do_shutdown(struct uart_ */ spin_lock_irqsave(&port->lock, flags); up->ier = 0; - serial_port_out(port, UART_IER, 0); + set_ier(up, 0); spin_unlock_irqrestore(&port->lock, flags); synchronize_irq(port->irq); @@ -2728,7 +2766,7 @@ serial8250_do_set_termios(struct uart_po if (up->capabilities & UART_CAP_RTOIE) up->ier |= UART_IER_RTOIE; - serial_port_out(port, UART_IER, up->ier); + set_ier(up, up->ier); if (up->capabilities & UART_CAP_EFR) { unsigned char efr = 0; @@ -3192,7 +3230,7 @@ EXPORT_SYMBOL_GPL(serial8250_set_default #ifdef CONFIG_SERIAL_8250_CONSOLE -static void serial8250_console_putchar(struct uart_port *port, int ch) +static void serial8250_console_putchar_locked(struct uart_port *port, int ch) { struct uart_8250_port *up = up_to_u8250p(port); @@ -3200,6 +3238,18 @@ static void serial8250_console_putchar(s serial_port_out(port, UART_TX, ch); } +static void serial8250_console_putchar(struct uart_port *port, int ch) +{ + struct uart_8250_port *up = up_to_u8250p(port); + unsigned int flags; + + wait_for_xmitr(up, UART_LSR_THRE); + + console_atomic_lock(&flags); + serial8250_console_putchar_locked(port, ch); + console_atomic_unlock(flags); +} + /* * Restore serial console when h/w power-off detected */ @@ -3221,6 +3271,42 @@ static void serial8250_console_restore(s serial8250_out_MCR(up, UART_MCR_DTR | UART_MCR_RTS); } +void serial8250_console_write_atomic(struct uart_8250_port *up, + const char *s, unsigned int count) +{ + struct uart_port *port = &up->port; + unsigned int flags; + bool locked; + + console_atomic_lock(&flags); + + /* + * If possible, keep any other CPUs from working with the + * UART until the atomic message is completed. This helps + * to keep the output more orderly. + */ + locked = spin_trylock(&port->lock); + + touch_nmi_watchdog(); + + clear_ier(up); + + if (atomic_fetch_inc(&up->console_printing)) { + uart_console_write(port, "\n", 1, + serial8250_console_putchar_locked); + } + uart_console_write(port, s, count, serial8250_console_putchar_locked); + atomic_dec(&up->console_printing); + + wait_for_xmitr(up, BOTH_EMPTY); + restore_ier(up); + + if (locked) + spin_unlock(&port->lock); + + console_atomic_unlock(flags); +} + /* * Print a string to the serial port trying not to disturb * any possible real use of the port... @@ -3232,27 +3318,13 @@ void serial8250_console_write(struct uar { struct uart_port *port = &up->port; unsigned long flags; - unsigned int ier; - int locked = 1; touch_nmi_watchdog(); serial8250_rpm_get(up); + spin_lock_irqsave(&port->lock, flags); - if (oops_in_progress) - locked = spin_trylock_irqsave(&port->lock, flags); - else - spin_lock_irqsave(&port->lock, flags); - - /* - * First save the IER then disable the interrupts - */ - ier = serial_port_in(port, UART_IER); - - if (up->capabilities & UART_CAP_UUE) - serial_port_out(port, UART_IER, UART_IER_UUE); - else - serial_port_out(port, UART_IER, 0); + clear_ier(up); /* check scratch reg to see if port powered off during system sleep */ if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) { @@ -3260,14 +3332,16 @@ void serial8250_console_write(struct uar up->canary = 0; } + atomic_inc(&up->console_printing); uart_console_write(port, s, count, serial8250_console_putchar); + atomic_dec(&up->console_printing); /* * Finally, wait for transmitter to become empty * and restore the IER */ wait_for_xmitr(up, BOTH_EMPTY); - serial_port_out(port, UART_IER, ier); + restore_ier(up); /* * The receive handling will happen properly because the @@ -3279,8 +3353,7 @@ void serial8250_console_write(struct uar if (up->msr_saved_flags) serial8250_modem_status(up); - if (locked) - spin_unlock_irqrestore(&port->lock, flags); + spin_unlock_irqrestore(&port->lock, flags); serial8250_rpm_put(up); } @@ -3301,6 +3374,7 @@ static unsigned int probe_baud(struct ua int serial8250_console_setup(struct uart_port *port, char *options, bool probe) { + struct uart_8250_port *up = up_to_u8250p(port); int baud = 9600; int bits = 8; int parity = 'n'; @@ -3309,6 +3383,8 @@ int serial8250_console_setup(struct uart if (!port->iobase && !port->membase) return -ENODEV; + atomic_set(&up->console_printing, 0); + if (options) uart_parse_options(options, &baud, &parity, &bits, &flow); else if (probe) --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -7,6 +7,7 @@ #ifndef _LINUX_SERIAL_8250_H #define _LINUX_SERIAL_8250_H +#include #include #include #include @@ -122,6 +123,8 @@ struct uart_8250_port { #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA unsigned char msr_saved_flags; + atomic_t console_printing; + struct uart_8250_dma *dma; const struct uart_8250_ops *ops; @@ -173,6 +176,8 @@ void serial8250_init_port(struct uart_82 void serial8250_set_defaults(struct uart_8250_port *up); void serial8250_console_write(struct uart_8250_port *up, const char *s, unsigned int count); +void serial8250_console_write_atomic(struct uart_8250_port *up, const char *s, + unsigned int count); int serial8250_console_setup(struct uart_port *port, char *options, bool probe); extern void serial8250_set_isa_configurator(void (*v)