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

Jeremy Fitzhardinge <jeremy@xxxxxxxx> writes:

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.

Still there's the effect that Ctrl-Z+kill works faster than Ctrl-C
that is not explained by this. This has often annoyed me too.
I'm not sure why it is. In theory they should be the same unless
someone blocks SIGINT.

-Andi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages