Re: [PATCH] NMI trigger switch support for debugging

From: Mikael Pettersson (mikpe_at_csd.uu.se)
Date: 05/26/04

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    Date:	Wed, 26 May 2004 11:43:09 +0200
To: AKIYAMA Nobuyuki <akiyama.nobuyuk@jp.fujitsu.com>

    AKIYAMA Nobuyuki writes:
    > +int unknown_nmi_panic = 0;

    It's a kernel coding standard to _not_ explicitly initialise
    static-extent data to zero.

    > +/*
    > + * proc handler for /proc/sys/kernel/unknown_nmi_panic
    > + */
    > +int proc_unknown_nmi_panic(ctl_table *table, int write,
    > + struct file *file, void __user *buffer, size_t *length)
    > +{
    > + int old_state;
    > +
    > + old_state = unknown_nmi_panic;
    > + proc_dointvec(table, write, file, buffer, length);
    > + if (!old_state == !unknown_nmi_panic)
    > + return 0;

    This conditional looks terribly obscure.
    Can you simplify it or explain your intention here?

    > + if (unknown_nmi_panic) {
    > + if (reserve_lapic_nmi() < 0) {
    > + unknown_nmi_panic = 0;
    > + return -EBUSY;
    > + } else {
    > + set_nmi_callback(unknown_nmi_panic_callback);
    > + }
    > + } else {
    > + release_lapic_nmi();

    You're invoking release_lapic_nmi() in response to user
    input, without having verified that _you_ had done a
    reserve_lapic_nmi() before.

    It looks like the code will do horrible things if the
    operator invokes the sysctl incorrectly. Such errors do
    happen, so code should include basic sanity checks.

    /Mikael
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