Messages in this thread Patch in this message | | | Date | Sat, 13 Nov 2010 07:18:30 +0300 | Subject | Re: [PATCH 11/19] 8250: Fix tcsetattr to avoid ioctl(TIOCMIWAIT) hang | From | Alexey Zaytsev <> |
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Hi.
This one kills the serial console for me. Luckily, in qemu:
(gdb) bt #0 __const_udelay (xloops=4295000) at arch/x86/lib/delay.c:117 #1 0xc137ab7c in panic (fmt=0xc147f8e1 "Attempted to kill the idle task!") at kernel/panic.c:151 #2 0xc1020731 in do_exit (code=9) at kernel/exit.c:915 #3 0xc100476a in oops_end (flags=70, regs=<value optimized out>, signr=9) at arch/x86/kernel/dumpstack.c:265 #4 0xc1014317 in no_context (regs=0xc14ebe68, error_code=<value optimized out>, address=192) at arch/x86/mm/fault.c:673 #5 0xc1014411 in __bad_area_nosemaphore (regs=0xc14ebe68, error_code=<value optimized out>, address=192, si_code=196609) at arch/x86/mm/fault.c:739 #6 0xc1014426 in bad_area_nosemaphore (regs=0x418958, error_code=81, address=3238124885) at arch/x86/mm/fault.c:746 #7 0xc101475a in do_page_fault (regs=0xc14ebe68, error_code=0) at arch/x86/mm/fault.c:1070 #8 0xc137ced9 in ?? () at arch/x86/kernel/entry_32.S:1265 #9 0xc11db236 in list_empty (head=0xc0) at include/linux/list.h:182 #10 0xc11db374 in waitqueue_active (q=0x98) at include/linux/wait.h:115 #11 0xc11dea4e in serial8250_do_set_termios (port=0xc1c31320, termios=0xc14ebf2c, old=0xc1c31240) at drivers/serial/8250.c:2349 #12 0xc11decb6 in serial8250_set_termios (port=0xc1c31320, termios=0xc14ebf2c, old=0xc1c31240) at drivers/serial/8250.c:2424 #13 0xc11da10b in uart_set_options (port=0xc1c31320, co=0xc164f0a0, baud=9600, parity=110, bits=8, flow=110) at drivers/serial/serial_core.c:1935 #14 0xc1684d30 in serial8250_console_setup (co=0xc164f0a0, options=0x0) at drivers/serial/8250.c:2864 #15 0xc101e46f in register_console (newcon=0xc164f0a0) at kernel/printk.c:1300 #16 0xc1684d5e in serial8250_console_init () at drivers/serial/8250.c:2889 #17 0xc1683da0 in console_init () at drivers/tty/tty_io.c:3208 #18 0xc166b7ba in start_kernel () at init/main.c:635 #19 0xc166b0b7 in i386_start_kernel () at arch/x86/kernel/head32.c:75 #20 0x00000000 in ?? () (gdb) p up->port.state $13 = (struct uart_state *) 0x0
On Sat, Nov 13, 2010 at 00:40, Greg Kroah-Hartman <gregkh@suse.de> wrote: > From: Lawrence Rust <lvr@softsystem.co.uk> > > 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 <stdio.h> > #include <errno.h> > #include <unistd.h> > #include <fcntl.h> > #include <pthread.h> > #include <termios.h> > #include <sys/ioctl.h> > #include <linux/serial.h> > > 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 <lawrence@softsystem.co.uk> > > Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> > --- > 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/ > -- 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/
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