From 47d3904fe40d62deee8cd46e79ca784e7a548acd Mon Sep 17 00:00:00 2001 From: Lawrence Rust Date: Wed, 27 Oct 2010 14:41:02 +0200 Subject: 8250: Fix tcsetattr to avoid ioctl(TIOCMIWAIT) hang Calling tcsetattr prevents any thread(s) currently suspended in ioctl TIOCMIWAIT for the same device from ever resuming. If a thread is suspended inside a call to ioctl TIOCMIWAIT, waiting for a modem status change, then the 8250 driver enables modem status interrupts (MSI). The device interrupt service routine resumes the suspended thread(s) on the next MSI. If while the thread(s) are suspended, another thread calls tcsetattr then the 8250 driver disables MSI (unless CTS/RTS handshaking is enabled) thus preventing the suspended thread(s) from ever being resumed. This patch only disables MSI in tcsetattr handling if there are no suspended threads. Program to demonstrate bug & fix: /* gcc miwait.c -o miwait -l pthread */ #include #include #include #include #include #include #include #include static void* monitor( void* pv); static int s_fd; int main( void) { const char kszDev[] = "/dev/ttyS0"; pthread_t t; struct termios tio; s_fd = open( kszDev, O_RDWR | O_NONBLOCK); if ( s_fd < 0) return fprintf( stderr, "Error(%d) opening %s: %s\n", errno, kszDev, strerror( errno)), 1; pthread_create( &t, NULL, &monitor, NULL); /* Modem status changes seen here */ puts( "Main: awaiting status changes"); sleep( 5); tcgetattr( s_fd, &tio); tio.c_cflag ^= CSTOPB; /* But not after here */ puts( "Main: tcsetattr called"); tcsetattr( s_fd, TCSANOW, &tio); for (;;) sleep( 1); } static void* monitor( void* pv) { (void)pv; for(;;) { unsigned uModem; struct serial_icounter_struct cnt; if ( ioctl( s_fd, TIOCMGET, &uModem) < 0) fprintf( stderr, "Error(%d) in TIOCMGET: %s\n", errno, strerror( errno)); printf( "Modem status:%s%s%s%s%s%s\n", (uModem & TIOCM_RTS) ? " RTS" : "", (uModem & TIOCM_DTR) ? " DTR" : "", (uModem & TIOCM_CTS) ? " CTS" : "", (uModem & TIOCM_DSR) ? " DSR" : "", (uModem & TIOCM_CD) ? " CD" : "", (uModem & TIOCM_RI) ? " RI" : "" ); if ( ioctl( s_fd, TIOCGICOUNT, &cnt) < 0) fprintf( stderr, "Error(%d) in TIOCGICOUNT: %s\n", errno, strerror( errno)); printf( "Irqs: CTS:%d DSR:%d RNG:%d DCD:%d Rx:%d Tx:%d Frame:%d Orun:%d Par:%d Brk:%d Oflow:%d\n", cnt.cts, cnt.dsr, cnt.rng, cnt.dcd, cnt.rx, cnt.tx, cnt.frame, cnt.overrun, cnt.parity, cnt.brk, cnt.buf_overrun ); fputs( "Waiting...", stdout), fflush( stdout); if ( 0 > ioctl( s_fd, TIOCMIWAIT, (unsigned long)(TIOCM_CAR | TIOCM_RNG | TIOCM_DSR | TIOCM_CTS))) fprintf( stderr, "\nError(%d) in TIOCMIWAIT: %s\n", errno, strerror( errno)); fputs( "\n", stdout); } return NULL; } Signed-off by Lawrence Rust Signed-off-by: Greg Kroah-Hartman --- drivers/serial/8250.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'drivers/serial/8250.c') diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index 4d8e14b7aa93..dd5e1ac22251 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -2343,8 +2343,11 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios, /* * CTS flow control flag and modem status interrupts + * Only disable MSI if no threads are waiting in + * serial_core::uart_wait_modem_status */ - up->ier &= ~UART_IER_MSI; + if (!waitqueue_active(&up->port.state->port.delta_msr_wait)) + up->ier &= ~UART_IER_MSI; if (!(up->bugs & UART_BUG_NOMSR) && UART_ENABLE_MS(&up->port, termios->c_cflag)) up->ier |= UART_IER_MSI; -- cgit v1.2.3 From f8b372a11cc102b9a0dcc6ac2bd10f0b6b2755a9 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Sat, 13 Nov 2010 16:21:58 +0100 Subject: Revert "8250: Fix tcsetattr to avoid ioctl(TIOCMIWAIT) hang" This reverts commit 47d3904fe40d62deee8cd46e79ca784e7a548acd. Crashes any x86 serial console bootup: Console: colour VGA+ 80x25 BUG: unable to handle kernel NULL pointer dereference at 0000000000000158 IP: [] serial8250_do_set_termios+0x1d4/0x430 ... Signed-off-by: Ingo Molnar Cc: Greg KH Cc: Andrew Morton Cc: Alan Cox Signed-off-by: Linus Torvalds --- drivers/serial/8250.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'drivers/serial/8250.c') diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index dd5e1ac22251..4d8e14b7aa93 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -2343,11 +2343,8 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios, /* * CTS flow control flag and modem status interrupts - * Only disable MSI if no threads are waiting in - * serial_core::uart_wait_modem_status */ - if (!waitqueue_active(&up->port.state->port.delta_msr_wait)) - up->ier &= ~UART_IER_MSI; + up->ier &= ~UART_IER_MSI; if (!(up->bugs & UART_BUG_NOMSR) && UART_ENABLE_MS(&up->port, termios->c_cflag)) up->ier |= UART_IER_MSI; -- cgit v1.2.3 From a80c49dbb6cd389fd5b0d79f850b56322475d00b Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 15 Nov 2010 21:11:12 +0100 Subject: serial8250: Mark console as CON_ANYTIME While trying to debug a cpu-hotplug issue I noticed printk() stopped working once the cpu got marked offline, since the 8250 serial console doesn't have any per-cpu resources the CON_ANYTIME bit is the safe and documented way to make it work again. Signed-off-by: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman --- drivers/serial/8250.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/serial/8250.c') diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index 4d8e14b7aa93..09a550860dcf 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -2872,7 +2872,7 @@ static struct console serial8250_console = { .device = uart_console_device, .setup = serial8250_console_setup, .early_setup = serial8250_console_early_setup, - .flags = CON_PRINTBUFFER, + .flags = CON_PRINTBUFFER | CON_ANYTIME, .index = -1, .data = &serial8250_reg, }; -- cgit v1.2.3