lkml.org 
[lkml]   [2007]   [Sep]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: WARNING: at arch/x86_64/kernel/smp.c:397 smp_call_function_mask()
    Fengguang Wu wrote:
    > On Thu, Sep 27, 2007 at 02:22:20AM -0700, Andrew Morton wrote:
    >> ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc8/2.6.23-rc8-mm2/
    >
    > Laurent,
    >
    > It triggered a WARNING on first run in qemu:

    Thank you to report it.

    >
    > [ 0.310000] WARNING: at arch/x86_64/kernel/smp.c:397 smp_call_function_mask()
    > [ 0.310000]
    > [ 0.310000] Call Trace:
    > [ 0.310000] [<ffffffff8100dbde>] dump_trace+0x3ee/0x4a0
    > [ 0.310000] [<ffffffff8100dcd3>] show_trace+0x43/0x70
    > [ 0.310000] [<ffffffff8100dd15>] dump_stack+0x15/0x20
    > [ 0.310000] [<ffffffff8101cd44>] smp_call_function_mask+0x94/0xa0
    > [ 0.310000] [<ffffffff8101cd69>] smp_call_function+0x19/0x20
    > [ 0.310000] [<ffffffff8104277f>] on_each_cpu+0x1f/0x50
    > [ 0.310000] [<ffffffff81026eac>] global_flush_tlb+0x8c/0x110
    > [ 0.310000] [<ffffffff81025c85>] free_init_pages+0xe5/0xf0
    > [ 0.310000] [<ffffffff81549b5e>] alternative_instructions+0x7e/0x150
    > [ 0.310000] [<ffffffff8154a2ea>] check_bugs+0x1a/0x20
    > [ 0.310000] [<ffffffff81540c4a>] start_kernel+0x2da/0x380
    > [ 0.310000] [<ffffffff81540132>] _sinittext+0x132/0x140


    the reason is the WARN_ON():

    390 int smp_call_function_mask(cpumask_t mask,
    391 void (*func)(void *), void *info,
    392 int wait)
    393 {
    394 int ret;
    395
    396 /* Can deadlock when called with interrupts disabled */
    397 WARN_ON(irqs_disabled());
    398
    399 spin_lock(&call_lock);
    400 ret = __smp_call_function_mask(mask, func, info, wait);
    401 spin_unlock(&call_lock);
    402 return ret;
    403 }

    The patch I sent to Andi didn't include this WARN_ON() and it's why I didn't
    find this issue. (see http://lkml.org/lkml/2007/8/24/101)

    smp_call_function_mask() is called by smp_call_function() which calls a function
    on all CPU except current.
    The comment of smp_call_function() specifies:
    ...
    * You must not call this function with disabled interrupts or from a
    * hardware interrupt handler or from a bottom half handler.
    * Actually there are a few legal cases, like panic.
    */

    So this WARN_ON() is correct, and the caller (global_flush_tlb()) doesn't follow
    this rule.

    I guess this WARN_ON() is only needed when we have current CPU in provided mask.
    So I think we should change:

    int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
    int wait)
    {
    return smp_call_function_mask(cpu_online_map, func, info, wait);
    }
    ("cpu_online_map" is a bad choice, comment also specifies: "run a function on
    all other CPU")

    to

    int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
    int wait)
    {
    int ret;
    cpumask_t allbutself;

    allbutself = cpu_online_map;
    cpu_clear(smp_processor_id(), allbutself);

    spin_lock(&call_lock);
    ret = __smp_call_function_mask(allbutself, func, info, wait);
    spin_unlock(&call_lock);
    return ret;
    }
    (which is smp_call_function_mask() without the WARN_ON() and without current cpu
    in the mask)

    Andi, is this correct ?
    Andrew, should I send a patch implementing this change ?

    Regards,
    Laurent
    --
    ------------- Laurent.Vivier@bull.net --------------
    "Software is hard" - Donald Knuth

    [unhandled content-type:application/pgp-signature]
    \
     
     \ /
      Last update: 2007-09-28 10:55    [W:0.034 / U:154.156 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site