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    SubjectRe: percpu related boot crash on x86 (was: Linux 2.6.38-rc1)

    * Tejun Heo <tj@kernel.org> wrote:

    > Hello,
    >
    > On Wed, Jan 19, 2011 at 02:56:23PM +0200, Pekka Enberg wrote:
    > > Is vmalloc() and vfree() supposed to work with interrupts disabled? I
    > > always thought they weren't which would mean something in
    > > pcpu_mem_alloc() needs changing...
    >
    > They aren't but percpu allocator doesn't call them with interrupts
    > disabled normally. It only happens during early boot before it's
    > enabled for the first time but this is an allowed exception. We'll
    > probably need to update the WARN_ON to consider the rare call path.
    > It also looks like something in that path is turning off/on IRQ
    > instead of saving/restoring it, so that probably needs to be changed
    > too but both aren't really critical.
    >
    > I think the real problem is a lot of unsigned int percpu allocations
    > added by 6c9ae009 (irq: use per_cpu kstat_irqs). percpu allocator
    > should be able to cope but it assumes that it would always be able to
    > allocate contiguous allocation map using vmalloc and that might be
    > failing, although I cannot readily see how or why that would happen
    > frequently on a 64bit machine.

    Btw., based on Peter's suggestion i tried the limit-bumping hack below - but it did
    not help, the crash still triggers on 5%-10% of all randconfig bootups.

    Thanks,

    Ingo

    From e2c013d28c8fe81cd30976dcd3058cc86c6285d3 Mon Sep 17 00:00:00 2001
    From: Ingo Molnar <mingo@elte.hu>
    Date: Wed, 19 Jan 2011 20:15:20 +0100
    Subject: [PATCH] <not for upstream> percpu: Increase allocation limits

    Might solve the boot crashes ...

    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    mm/percpu.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/mm/percpu.c b/mm/percpu.c
    index 3f93001..5cd9cf4 100644
    --- a/mm/percpu.c
    +++ b/mm/percpu.c
    @@ -74,7 +74,7 @@
    #include <asm/io.h>

    #define PCPU_SLOT_BASE_SHIFT 5 /* 1-31 shares the same slot */
    -#define PCPU_DFL_MAP_ALLOC 16 /* start a map with 16 ents */
    +#define PCPU_DFL_MAP_ALLOC 64 /* start a map with 64 ents */

    #ifdef CONFIG_SMP
    /* default addr <-> pcpu_ptr mapping, override in asm/percpu.h if necessary */

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