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

[Avi Kivity <avi@qumranet.com>]

Jeremy Fitzhardinge wrote:
> Török Edwin wrote:
>> Hi,
>>
>> I have encountered the following situation several times, but I've been
>> unable to come up with a way to reproduce this until now:
>>  - some process is keeping the disk busy (some cron job for example:
>> updatedb, chkrootkit, ...)
>>  - other processes that want to do I/O have to wait (this is normal)
>>  - I have a (I/O bound) process running in my terminal, and I want to
>> interrupt it with Ctrl+C
>>  - I type Ctrl+C several times, and the process is not interrupted for
>> several seconds (10-30 secs)
>>  - if I type Ctrl+Z, and use kill %1 the process dies faster than
>> waiting for it to react to Ctrl+C
>>
>> This issue occurs both on my x86-64 machine that uses reiserfs, and on
>> my x86 machine that uses XFS, so it doesn't seem related to the
>> underlying FS.
>> I use 2.6.25-2 and 2.6.26-rc8 now; I don't recall seeing this behaviour
>> with old kernels (IIRC I see this since 2.6.21 or 2.6.23).
>>
>> Is this intended behaviour, or should I report a bug?
>>   
>
> 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).

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.