dd hangs with SIGINT

[Guillaume Chazarain <guichaz@yahoo.fr>]

Hi,

With recent linux distributions (using NPTL), I noticed that dd can hang
waiting on a futex when being killed. The problem sould be reproduceable
with the following script :

-------$<-------$<-------$<-------$<-------$<-------$<-------$<--------

#!/bin/sh

echo 'When you only see "dd frozen" in a loop the problem is present'

while : ; do
   dd if=/dev/zero of=/dev/null bs=1000 count=200 &> /dev/null
   echo -n "."
done &

# Don't leave useless dd processes
CHILD=$!
trap "kill $CHILD; killall dd" EXIT

while : ; do
   killall -INT dd &> /dev/null
   usleep 10000
   PIDOF_DD1=$(pidof dd)
   usleep 10000
   PIDOF_DD2=$(pidof dd)
   if [ -n "$PIDOF_DD1" ] && [ "$PIDOF_DD1" = "$PIDOF_DD2" ]; then
       echo "dd frozen"
   else
       echo -n "+"
   fi
done

-------$<-------$<-------$<-------$<-------$<-------$<-------$<--------

I can reproduce it on Fedora Core [1-3] on x86, even with recent kernels
like 2.6.12-rc1-bk3,,but it goes away with LD_ASSUME_KERNEL=2.4. It
seems to exploit a race condition somewhere, so the problem may need
some time (or some load) before triggering.


Hopefully someone can reproduce and look into it.
Kind regards.

--
Guillaume

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