Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933158Ab0KLVnE (ORCPT ); Fri, 12 Nov 2010 16:43:04 -0500 Received: from kroah.org ([198.145.64.141]:41597 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933064Ab0KLVlO (ORCPT ); Fri, 12 Nov 2010 16:41:14 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Lawrence Rust , Greg Kroah-Hartman Subject: [PATCH 11/19] 8250: Fix tcsetattr to avoid ioctl(TIOCMIWAIT) hang Date: Fri, 12 Nov 2010 13:40:58 -0800 Message-Id: <1289598066-10112-11-git-send-email-gregkh@suse.de> X-Mailer: git-send-email 1.7.1 In-Reply-To: <20101112213215.GB9294@kroah.com> References: <20101112213215.GB9294@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3880 Lines: 127 From: Lawrence Rust 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 files changed, 4 insertions(+), 1 deletions(-) diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index 4d8e14b..dd5e1ac 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; -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/