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SubjectRe: Ctrl+C doesn't interrupt process waiting for I/O
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 said, if a program is blocking for tens of seconds in block IO,
then that could be a problem in itself.

J
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