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    Subject[PATCH v1 08/15] futex: UP futex_atomic_op_inuser() relies on disabled preemption
    Date
    Let's explicitly disable/enable preemption in the !CONFIG_SMP version
    of futex_atomic_op_inuser, to prepare for pagefault_disable() not
    touching preemption anymore.

    Otherwise we might break mutual exclusion when relying on a get_user()/
    put_user() implementation.

    Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
    ---
    include/asm-generic/futex.h | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
    index b59b5a5..3586017 100644
    --- a/include/asm-generic/futex.h
    +++ b/include/asm-generic/futex.h
    @@ -8,8 +8,7 @@
    #ifndef CONFIG_SMP
    /*
    * The following implementation only for uniprocessor machines.
    - * For UP, it's relies on the fact that pagefault_disable() also disables
    - * preemption to ensure mutual exclusion.
    + * It relies on preempt_disable() ensuring mutual exclusion.
    *
    */

    @@ -38,6 +37,7 @@ futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
    if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
    oparg = 1 << oparg;

    + preempt_disable();
    pagefault_disable();

    ret = -EFAULT;
    @@ -72,6 +72,7 @@ futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)

    out_pagefault_enable:
    pagefault_enable();
    + preempt_enable();

    if (ret == 0) {
    switch (cmp) {
    --
    2.1.4


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