ttyS0 stuck in tty_wait_until_sent when sending break (opened with O_NONBLOCK)

From: Domen Puncer
Date: Sun Nov 06 2011 - 05:27:23 EST

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Hello!

I'm not able to create a simple program, that would reproduce this
problem, but calling OW_init()
from libowcapi and with nothing plugged into serial seems to always do
the trick.

$ cat /proc/`pidof test`/wchan; echo
tty_wait_until_sent

$ uname -a
Linux river 3.0-ARCH #1 SMP PREEMPT Wed Oct 19 10:27:51 CEST 2011
x86_64 Intel(R) Core(TM)2 Duo CPU E6750 @ 2.66GHz GenuineIntel
GNU/Linux
But I've also seen this on an older mips kernel.

Is there any way I can assist hunting this down?
I'll try harder to make a simple test program, if the strace output
doesn't produce any ideas.

strace output:

open("/dev/ttyS0", O_RDWR|O_NOCTTY|O_NONBLOCK) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
TCGETS, {B115200 -opost -isig -icanon -echo ...}) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
TCGETS, {B115200 -opost -isig -icanon -echo ...}) = 0
ioctl(3, SNDCTL_TMR_CONTINUE or SNDRV_TIMER_IOCTL_GPARAMS or TCSETSF,
{B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, TCFLSH, 0x2) = 0
ioctl(3, TCSBRK, 0) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999995})
write(3, "\301", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 4000000}, 0x7fff2d209ba0) = 0
ioctl(3, TCFLSH, 0x2) = 0
select(4, [3], NULL, NULL, {0, 1000}) = 0 (Timeout)
ioctl(3, TCFLSH, 0x2) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "q", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
TCGETS, {B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, SNDCTL_TMR_CONTINUE or SNDRV_TIMER_IOCTL_GPARAMS or TCSETSF,
{B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, TCFLSH, 0x2) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
select(4, [3], NULL, NULL, {0, 1000}) = 0 (Timeout)
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "\17", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
ioctl(3, TCFLSH, 0x2) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "\305", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 400000000}, 0x7fff2d209ba0) = 0
ioctl(3, TCFLSH, 0x2) = 0
select(4, [3], NULL, NULL, {0, 1000}) = 0 (Timeout)
ioctl(3, TCFLSH, 0x2) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999997})
write(3, "q", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
TCGETS, {B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, SNDCTL_TMR_CONTINUE or SNDRV_TIMER_IOCTL_GPARAMS or TCSETSF,
{B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, TCFLSH, 0x2) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
select(4, [3], NULL, NULL, {0, 1000}) = 0 (Timeout)
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "\17", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
ioctl(3, TCFLSH, 0x2) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "\305", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 4000000}, 0x7fff2d209ba0) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999997})
write(3, "E", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
close(3) = 0
open("/dev/ttyS0", O_RDWR|O_NOCTTY|O_NONBLOCK) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
TCGETS, {B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, SNDCTL_TMR_CONTINUE or SNDRV_TIMER_IOCTL_GPARAMS or TCSETSF,
{B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, TCFLSH, 0x2) = 0
ioctl(3, TCSBRK, 0) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999996})
write(3, "\301", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 4000000}, 0x7fff2d209ba0) = 0
ioctl(3, TCFLSH, 0x2) = 0
select(4, [3], NULL, NULL, {0, 1000}) = 0 (Timeout)
ioctl(3, TCFLSH, 0x2) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "q", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
TCGETS, {B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, SNDCTL_TMR_CONTINUE or SNDRV_TIMER_IOCTL_GPARAMS or TCSETSF,
{B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, TCFLSH, 0x2) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
select(4, [3], NULL, NULL, {0, 1000}) = 0 (Timeout)
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "\17", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
ioctl(3, TCFLSH, 0x2) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "\305", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 400000000}, 0x7fff2d209ba0) = 0
ioctl(3, TCFLSH, 0x2) = 0
select(4, [3], NULL, NULL, {0, 1000}) = 0 (Timeout)
ioctl(3, TCFLSH, 0x2) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999997})
write(3, "q", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
TCGETS, {B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, SNDCTL_TMR_CONTINUE or SNDRV_TIMER_IOCTL_GPARAMS or TCSETSF,
{B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, TCFLSH, 0x2) = 0
nanosleep({0, 5000000}, 0x7fff2d209b20) = 0
select(4, [3], NULL, NULL, {0, 1000}) = 0 (Timeout)
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999998})
write(3, "\17", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
ioctl(3, TCFLSH, 0x2) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999997})
write(3, "\305", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
nanosleep({0, 4000000}, 0x7fff2d209ba0) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999995})
write(3, "E", 1) = 1
ioctl(3, TCSBRK, 0x1) = 0
select(4, [3], NULL, NULL, {5, 0}) = 0 (Timeout)
ioctl(3, TCSBRK, 0x1) = 0
close(3) = 0
open("/dev/ttyS0", O_RDWR|O_NOCTTY|O_NONBLOCK) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
TCGETS, {B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, SNDCTL_TMR_CONTINUE or SNDRV_TIMER_IOCTL_GPARAMS or TCSETSF,
{B9600 -opost -isig -icanon -echo ...}) = 0
ioctl(3, TCFLSH, 0x2) = 0
ioctl(3, TCSBRK, 0) = 0
select(4, NULL, [3], NULL, {5, 0}) = 1 (out [3], left {4, 999997})
write(3, "\301", 1) = 1
ioctl(3, TCSBRK <unfinished ...>
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Next message: Pekka Enberg: "Re: [PATCH] KVM: Add wrapper script around QEMU to test kernels"
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