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

[Avi Kivity]

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.

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