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    SubjectRe: [PATCH] X86: reboot-notify additions

    * Cliff Wickman <cpw@sgi.com> wrote:

    > From: Cliff Wickman <cpw@sgi.com>
    >
    > X86 reboot-notify additions.
    >
    > This patch adds scans of the "reboot_notifier_list" callback chain in
    > a three other places where the kernel is being stopped and/or restarted.
    >
    > Adds calls to blocking_notifier_call_chain() in:
    > crash_kexec(), emergency_restart(), sys_kexec_load()
    >
    > In the crash_kexec() and emergency_restart() cases it is indicated to the
    > called-back function that the system is not in a sane state, so that
    > it can avoid taking a lock or some such potentially blocking action.
    >
    > These callbacks are important to a partition system. The stopped kernel needs
    > to inform other partitions of their need to disconnect (stop sharing memory).
    >
    > Diffed against 2.6.26-rc6
    >
    > Signed-off-by: Cliff Wickman <cpw@sgi.com>
    > ---
    > include/linux/notifier.h | 4 ++++
    > kernel/kexec.c | 5 +++++
    > kernel/sys.c | 1 +
    > 3 files changed, 10 insertions(+)
    >
    > Index: linux/include/linux/notifier.h
    > ===================================================================
    > --- linux.orig/include/linux/notifier.h
    > +++ linux/include/linux/notifier.h
    > @@ -202,6 +202,10 @@ static inline int notifier_to_errno(int
    > #define SYS_RESTART SYS_DOWN
    > #define SYS_HALT 0x0002 /* Notify of system halt */
    > #define SYS_POWER_OFF 0x0003 /* Notify of system power off */
    > +#define SYS_INSANE 0x0004 /* Notify of system error/panic/oops */
    > +/* For the SYS_INSANE case, no locks should be taken by the called-back
    > + * function. The kernel is ready for an immediate reboot.
    > + */
    >
    > #define NETLINK_URELEASE 0x0001 /* Unicast netlink socket released */
    >
    > Index: linux/kernel/kexec.c
    > ===================================================================
    > --- linux.orig/kernel/kexec.c
    > +++ linux/kernel/kexec.c
    > @@ -1001,6 +1001,9 @@ asmlinkage long sys_kexec_load(unsigned
    > if (result)
    > goto out;
    > }
    > +
    > + blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, NULL);
    > +
    > /* Install the new kernel, and Uninstall the old */
    > image = xchg(dest_image, image);
    >
    > @@ -1068,6 +1071,8 @@ void crash_kexec(struct pt_regs *regs)
    > if (!locked) {
    > if (kexec_crash_image) {
    > struct pt_regs fixed_regs;
    > + blocking_notifier_call_chain(&reboot_notifier_list,
    > + SYS_INSANE, NULL);
    > crash_setup_regs(&fixed_regs, regs);
    > crash_save_vmcoreinfo();
    > machine_crash_shutdown(&fixed_regs);
    > Index: linux/kernel/sys.c
    > ===================================================================
    > --- linux.orig/kernel/sys.c
    > +++ linux/kernel/sys.c
    > @@ -270,6 +270,7 @@ out_unlock:
    > */
    > void emergency_restart(void)
    > {
    > + blocking_notifier_call_chain(&reboot_notifier_list, SYS_INSANE, NULL);
    > machine_emergency_restart();
    > }
    > EXPORT_SYMBOL_GPL(emergency_restart);

    i dont think this is a good idea. reboot_notifier_list is a blocking
    notifier, i.e. it comes with a notifier->rwsem read-write mutex that is
    taken when blocking_notifier_call_chain() is executed.

    i.e. this patch puts a sleeping mutex operation (a down_read()) into a
    highly critical code path of the kernel. This will decrease the
    reliability of the kernel.

    what exactly are you trying to achieve?

    Ingo


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