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Subject3.0.18 tcsetattr on fd 0 when detached freezes system (RCU timeouts) (Centos 6.1 x86_64)

typedef struct
{
struct termios term;
} XKEY_DATA;

typedef XKEY_DATA *xkeyhandle;

static inline xkeyhandle xkeystart()
{

// Turn off echo.
struct termios temp;
err = tcgetattr(0, &temp);
if (err)
{
perror("tcgetattr failure");
}

XKEY_DATA *handle = new XKEY_DATA;
handle->term = temp;

temp.c_lflag &= ~ECHO;
temp.c_lflag &= ~ICANON;

err = tcsetattr(0, TCSANOW, &temp); // this line causes the
kernel to get very sick
if (err)
{
perror("tcsetattr failure");
}

return handle;

}

The above code, called from main() will produce an error from tcsh:

/home/bshands> ./a.out > /dev/null &
[1] 3635
/home/bshands>
/home/bshands>
[1] + Suspended (tty output) ./a.out > /dev/null
/home/bshands>

this does not appear on the redhat kernel, nor 2.6.32.43, but appeared
infrequently in 3.0.9.
in 3.0.18, doing this in the background does *EVIL* things.

ssh system "./a.out > /dev/null &" &

Now when the code reaches the tcsetattr() the system quits scheduling tasks.
top shows 100%sy on 4/12 cores, kernel threads blocked, stalled tasks
count increasing.


Jan 27 18:58:50 system kernel: [ 1269.891610] kjournald S
ffff880321270a30 0 416 2 0x00000000
Jan 27 18:58:50 system kernel: [ 1269.891684] ffff880321f5de50
0000000000000046 ffff880321270680 0000000000000000
Jan 27 18:58:50 system kernel: [ 1269.891816] ffff880321270680
0000000000012ac0 ffff880321f5dfd8 ffff880321f5c010
Jan 27 18:58:50 system kernel: [ 1269.891948] ffff880321f5dfd8
0000000000012ac0 ffff880327a61260 ffff880321270680
Jan 27 18:58:50 system kernel: [ 1269.892083] Call Trace:
Jan 27 18:58:50 system kernel: [ 1269.892144] [<ffffffff824c126f>]
schedule+0x3f/0x60
Jan 27 18:58:50 system kernel: [ 1269.892226] [<ffffffffa0030f9d>]
kjournald+0x20d/0x230 [jbd]
Jan 27 18:58:50 system kernel: [ 1269.892294] [<ffffffff82082230>] ?
wake_up_bit+0x40/0x40
Jan 27 18:58:50 system kernel: [ 1269.892362] [<ffffffffa0030d90>] ?
commit_timeout+0x10/0x10 [jbd]
Jan 27 18:58:50 system kernel: [ 1269.892431] [<ffffffff82081bb6>]
kthread+0x96/0xa0
Jan 27 18:58:50 system kernel: [ 1269.892497] [<ffffffff824cbe04>]
kernel_thread_helper+0x4/0x10
Jan 27 18:58:50 system kernel: [ 1269.892565] [<ffffffff82081b20>] ?
kthread_worker_fn+0x1a0/0x1a0
Jan 27 18:58:50 system kernel: [ 1269.892633] [<ffffffff824cbe00>] ?
gs_change+0x13/0x13

After a little while, the system locks up. rcu timeout errors may appear
in dmesg.
dumps are available.

Note that this little bugger is a user mode crash, once started, you are
done.
it appears that later use of termios is still sufficient to trigger the
lockup.
they key is being detached.

Berkley







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