lkml.org 
[lkml]   [2006]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH] Check for online cpus before bringing them up
    On Thu, Mar 16, 2006 at 05:08:14PM -0800, Andrew Morton wrote:
    > Is x86 the only architecture which is exposed to this?

    Currently only x86 implements smp_prepare_cpu(). On other arch, it is a
    no-op. Hence yes, only x86 is exposed to this bug.

    > >
    > > lock_cpu_hotplug();
    > > +
    > > + if (cpu_online(cpu)) {
    > > + ret = -EINVAL;
    > > + goto exit;
    > > + }
    > > +
    > > apicid = x86_cpu_to_apicid[cpu];
    > > if (apicid == BAD_APICID) {
    > > ret = -ENODEV;
    >
    > a) It's hard for the reader to understand what that test is doing there
    >
    > b) People copy code from x86, so other architectures which are not
    > exposed to this problem will end up having a pointless test in there.

    Well ..other arch-es need to have a similar check if they get around to
    implement physical hot-add (even if they allow offlining of all CPUs). This is
    required since a user can (by mistake maybe) try to bring up an already online
    CPU by writing a '1' to it's sysfs 'online' file. 'store_online'
    (drivers/base/cpu.c) unconditionally calls 'smp_prepare_cpu' w/o checking for
    this error condition. The check added in the patch catches such error
    conditions as well.

    > IOW: please comment your code. I'll fix this one up.

    Sorry about not commenting my code earlier! How does the patch below look?


    Add check for online cpus.

    Signed-off-by : Srivatsa Vaddagiri <vatsa@in.ibm.com>


    arch/i386/kernel/smpboot.c | 10 ++++++++++
    1 files changed, 10 insertions(+)

    diff -puN arch/i386/kernel/smpboot.c~cpu_hp arch/i386/kernel/smpboot.c
    --- linux-2.6.16-rc6/arch/i386/kernel/smpboot.c~cpu_hp 2006-03-17 14:27:15.000000000 +0530
    +++ linux-2.6.16-rc6-root/arch/i386/kernel/smpboot.c 2006-03-17 14:38:50.000000000 +0530
    @@ -1029,6 +1029,16 @@ int __devinit smp_prepare_cpu(int cpu)
    int apicid, ret;

    lock_cpu_hotplug();
    +
    + /* Check if CPU is already online. This can happen if user tries to
    + * bringup an already online CPU or a previous offline attempt
    + * on this CPU has failed.
    + */
    + if (cpu_online(cpu)) {
    + ret = -EINVAL;
    + goto exit;
    + }
    +
    apicid = x86_cpu_to_apicid[cpu];
    if (apicid == BAD_APICID) {
    ret = -ENODEV;
    _

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

    \
     
     \ /
      Last update: 2006-03-17 09:49    [W:0.024 / U:61.984 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site