linux-kernel - Re: Ctrl+C doesn't interrupt process waiting for I/O

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Message-ID: <48671FF6.1070501@qumranet.com>
Date:	Sun, 29 Jun 2008 08:39:02 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Török Edwin <edwintorok@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Ctrl+C doesn't interrupt process waiting for I/O

Jeremy Fitzhardinge wrote:
> Avi Kivity wrote:
>>>
>>> Yes, it's intended behaviour.  Filesystem IO syscalls are considered 
>>> "fast" and are interruptible.  Usermode code can reasonably expect 
>>> that file IO will never return EINTR.
>>
>> That's filesystem dependent; if you mount an nfs filesystem with the 
>> 'intr' mount option, it will be interruptible (which makes sense, as 
>> it is impossible to guarantee the server's responsiveness).
>
> 'intr' is a pretty bad idea, and I would never recommend it ('soft' is 
> better).  It's an excellent way to destroy data when a stray signal 
> causes a syscall to fail with EINTR in an unexpected way (write being 
> the obvious one, but link, unlink, truncate or even close can fail in 
> odd ways can cause havok).
>

Applications should not assume that write() (or other syscalls) can't 
return EINTR.  Not all filesystems have a bounded-time backing store.

'soft' has its own problems; namely false positives when someone steps 
on the network cable, temporarily blocking packet flow, or when using a 
clustered server which may take some time to recover from a fault.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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