TASKSET(1)                    Linux User’s Manual                   TASKSET(1)

       taskset - retrieve or set a process’s CPU affinity

       taskset [options] mask command [arg]...
       taskset [options] -p [mask] pid

       taskset  is used to set or retrieve the CPU affinity of a running process given its PID or to launch a new COMMAND with a given CPU affinity.  CPU affinity
       is a scheduler property that "bonds" a process to a given set of CPUs on the system.  The Linux scheduler will honor the given CPU affinity and the process
       will not run on any other CPUs.  Note that the Linux scheduler also supports natural CPU affinity: the scheduler attempts to keep processes on the same CPU
       as long as practical for performance reasons.  Therefore, forcing a specific CPU affinity is useful only in certain applications.

       The CPU affinity is represented as a bitmask, with the lowest order bit corresponding to the first logical CPU and the highest order bit  corresponding  to
       the  last logical CPU.  Not all CPUs may exist on a given system but a mask may specify more CPUs than are present.  A retrieved mask will reflect only the
       bits that correspond to CPUs physically on the system.  If an invalid mask is given (i.e., one that corresponds to no valid CPUs on the current system)  an
       error is returned.  The masks are typically given in hexadecimal.  For example,

              is processor #0

              is processors #0 and #1

              is all processors (#0 through #31)

       When taskset returns, it is guaranteed that the given program has been scheduled to a legal CPU.

       -p, --pid
              operate on an existing PID and not launch a new task

       -c, --cpu-list
              specify  a  numerical  list  of processors instead of a bitmask.  The list may contain multiple items, separated by comma, and ranges.  For example,

       -h, --help
              display usage information and exit

       -V, --version
              output version information and exit

       The default behavior is to run a new command with a given affinity mask:
              taskset mask command [arguments]

       You can also retrieve the CPU affinity of an existing task:
              taskset -p pid

       Or set it:
              taskset -p mask pid

       A user must possess CAP_SYS_NICE to change the CPU affinity of a process.  Any user can retrieve the affinity mask.

       Written by Robert M. Love.


Description of problem:

Install Fedora 9 (sorry, I can not find the entry for F9 bug report). 
Set one task affinity to one CPU core, then set offline the CPU core. After that
we can not set online the CPU core again.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1.  run the test.sh script:   test.sh 1  ( 1 is the logical CPU )
test.sh script:


    typeset -i CPU=$1
    ./task.sh > /dev/null&

    if [ `cat /sys/devices/system/cpu/cpu${CPU}/online` = "0" ]; then
        echo "1" > /sys/devices/system/cpu/cpu${CPU}/online


    `taskset -p ${MASK} ${PID} > /dev/null 2>&1`

    echo "0" > /sys/devices/system/cpu/cpu${CPU}/online

    echo "1" > /sys/devices/system/cpu/cpu${CPU}/online

    disown $PID
    kill -9 $PID > /dev/null 2>&1

    echo "PASS\n"


typeset -i TEST_CPU=$1
main $TEST_CPU

2. task.sh script as following


while :

Actual results:

The test.sh will block at set online the CPU ( echo "1" >
/sys/devices/system/cpu/cpu${CPU}/online ). 

Expected results:

Additional info:
Happened in Intel Bensley platform (2xXeon 2.83G Harpertown C0, chipset
Blackford G1, 160 SATA)  
------- Comment #1 >From Bill Nottingham 2008-02-18 13:07:03 EDT -------
Does this happen on the upstream kernel as well?  
------- Comment #2 >From Song, Youquan 2008-02-21 03:59:48 EDT -------
Yes. the kernel 2.6.24 to 2.6.25-rc2 also exit the bug. 
But the bug is not exit at kernel 2.6.18.   
------- Comment #3 >From Chuck Ebbert 2008-02-25 17:33:21 EDT -------
Does the CPU mask of the running process get changed when the processor is

And can you get a system state (alt-sysrq-t) when the script hangs?  
------- Comment #4 >From Song, Youquan 2008-02-27 04:15:50 EDT -------
Yes, after I set offline the CPU, I use commands "taskset -p $PID and ps --
pid=$PID -o psr" to find that process CPU mask is change and process migrate 
to other CPU correctly.
Attachment is the Screenshot.png  
------- Comment #5 >From Song, Youquan 2008-02-27 04:18:13 EDT -------
Created an attachment (id=296037) [details]
CPU can not  do hotplug when one task  set affinity to it.
------- Comment #6 >From Song, Youquan 2008-02-27 05:02:48 EDT -------
Created an attachment (id=296040) [details]
Alt-Sysrq-t log after run the script
------- Comment #7 >From Song, Youquan 2008-04-11 07:17:23 EDT -------
This bug is still exits on FC9 Beta.  
------- Comment #8 >From Bug Zapper 2008-05-14 01:12:51 EDT -------
Changing version to '9' as part of upcoming Fedora 9 GA.
More information and reason for this action is here:

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