Re: select, jiffies, and SIGALRM

[Robert Hancock <hancockr@shaw.ca>]

I see calls to getitimer, so I'm assuming it's also using setitimer. SIGALRM 
is what you get when those timers go off - if it's not handling that, that's 
a bug, but presumably the timer is in there for a reason..


----- Original Message ----- 
From: "Vx Glenn" <VxGlenn@gmail.com>
Newsgroups: fa.linux.kernel
To: <linux-net@vger.kernel.org>; <linux-kernel@vger.kernel.org>
Sent: Wednesday, October 13, 2004 10:13 AM
Subject: select, jiffies, and SIGALRM


> Hi all,
>
> I am seeing an issue relating to the jiffies counter wrapping around
> at 0x7FFFFFFF.
>
> This is a legacy application, and when it runs on 32-bit Unix-Like
> OS's, the application silently dies without leaving core after 248
> days.
>
> I was able to manipulate the jiffies counter and run the application.
> I was able to reproduce the problem. I captured an strace log, and I
> see that SIGALRM (alarm clock) is raised after select times out
> (because of no data).
>
> I can add a signal handler to intercept the SIGALRM. But my question
> is, why should the signal be raised?
>
> ---[ strace.log ]---
> select(1024, [3 4 5 6], NULL, NULL, {0, 320000}) = 0 (Timeout)
> getitimer(ITIMER_REAL, {it_interval={2147157, 520}, it_value={0, 684895}}) 
> = 0
> adjtimex({modes=32769, offset=0, freq=0, maxerror=16384000,
> esterror=16384000, status=64, constant=2, precision=1,
> tolerance=33554432, time={1097551596, 43475}}) = 5
> getitimer(ITIMER_REAL, {it_interval={2147157, 520}, it_value={0, 684895}}) 
> = 0
> select(1024, [3 4 5 6], NULL, NULL, {1, 0}) = ? ERESTARTNOHAND (To be 
> restarted)
> --- SIGALRM (Alarm clock) @ 0 (0) ---
> Process 4881 detached
> ---[ eof strace.log ]---
>
>
> Anyone have any ideas?
>
>
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