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    Subject[tip:core/debug] debug lockups: Improve lockup detection, fix generic arch fallback
    Commit-ID:  47cab6a722d44c71c4f8224017ef548522243cf4
    Gitweb: http://git.kernel.org/tip/47cab6a722d44c71c4f8224017ef548522243cf4
    Author: Ingo Molnar <mingo@elte.hu>
    AuthorDate: Mon, 3 Aug 2009 09:31:54 +0200
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Mon, 3 Aug 2009 09:56:52 +0200

    debug lockups: Improve lockup detection, fix generic arch fallback

    As Andrew noted, my previous patch ("debug lockups: Improve lockup
    detection") broke/removed SysRq-L support from architecture that do
    not provide a __trigger_all_cpu_backtrace implementation.

    Restore a fallback path and clean up the SysRq-L machinery a bit:

    - Rename the arch method to arch_trigger_all_cpu_backtrace()

    - Simplify the define

    - Document the method a bit - in the hope of more architectures
    adding support for it.

    [ The patch touches Sparc code for the rename. ]

    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: "David S. Miller" <davem@davemloft.net>
    LKML-Reference: <20090802140809.7ec4bb6b.akpm@linux-foundation.org>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


    ---
    arch/sparc/include/asm/irq_64.h | 4 ++--
    arch/sparc/kernel/process_64.c | 4 ++--
    arch/x86/include/asm/nmi.h | 4 ++--
    arch/x86/kernel/apic/nmi.c | 2 +-
    drivers/char/sysrq.c | 15 ++++++++++++++-
    include/linux/nmi.h | 19 +++++++++++++++++--
    6 files changed, 38 insertions(+), 10 deletions(-)

    diff --git a/arch/sparc/include/asm/irq_64.h b/arch/sparc/include/asm/irq_64.h
    index 1934f2c..a0b443c 100644
    --- a/arch/sparc/include/asm/irq_64.h
    +++ b/arch/sparc/include/asm/irq_64.h
    @@ -89,8 +89,8 @@ static inline unsigned long get_softint(void)
    return retval;
    }

    -void __trigger_all_cpu_backtrace(void);
    -#define trigger_all_cpu_backtrace() __trigger_all_cpu_backtrace()
    +void arch_trigger_all_cpu_backtrace(void);
    +#define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace

    extern void *hardirq_stack[NR_CPUS];
    extern void *softirq_stack[NR_CPUS];
    diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
    index 4041f94..18d6785 100644
    --- a/arch/sparc/kernel/process_64.c
    +++ b/arch/sparc/kernel/process_64.c
    @@ -251,7 +251,7 @@ static void __global_reg_poll(struct global_reg_snapshot *gp)
    }
    }

    -void __trigger_all_cpu_backtrace(void)
    +void arch_trigger_all_cpu_backtrace(void)
    {
    struct thread_info *tp = current_thread_info();
    struct pt_regs *regs = get_irq_regs();
    @@ -304,7 +304,7 @@ void __trigger_all_cpu_backtrace(void)

    static void sysrq_handle_globreg(int key, struct tty_struct *tty)
    {
    - __trigger_all_cpu_backtrace();
    + arch_trigger_all_cpu_backtrace();
    }

    static struct sysrq_key_op sparc_globalreg_op = {
    diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
    index c86e5ed..e63cf7d 100644
    --- a/arch/x86/include/asm/nmi.h
    +++ b/arch/x86/include/asm/nmi.h
    @@ -45,8 +45,8 @@ extern int proc_nmi_enabled(struct ctl_table *, int , struct file *,
    void __user *, size_t *, loff_t *);
    extern int unknown_nmi_panic;

    -void __trigger_all_cpu_backtrace(void);
    -#define trigger_all_cpu_backtrace() __trigger_all_cpu_backtrace()
    +void arch_trigger_all_cpu_backtrace(void);
    +#define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace

    static inline void localise_nmi_watchdog(void)
    {
    diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c
    index 1bb1ac2..db72202 100644
    --- a/arch/x86/kernel/apic/nmi.c
    +++ b/arch/x86/kernel/apic/nmi.c
    @@ -554,7 +554,7 @@ int do_nmi_callback(struct pt_regs *regs, int cpu)
    return 0;
    }

    -void __trigger_all_cpu_backtrace(void)
    +void arch_trigger_all_cpu_backtrace(void)
    {
    int i;

    diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
    index 165f307..50eecfe 100644
    --- a/drivers/char/sysrq.c
    +++ b/drivers/char/sysrq.c
    @@ -223,7 +223,20 @@ static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);

    static void sysrq_handle_showallcpus(int key, struct tty_struct *tty)
    {
    - trigger_all_cpu_backtrace();
    + /*
    + * Fall back to the workqueue based printing if the
    + * backtrace printing did not succeed or the
    + * architecture has no support for it:
    + */
    + if (!trigger_all_cpu_backtrace()) {
    + struct pt_regs *regs = get_irq_regs();
    +
    + if (regs) {
    + printk(KERN_INFO "CPU%d:\n", smp_processor_id());
    + show_regs(regs);
    + }
    + schedule_work(&sysrq_showallcpus);
    + }
    }

    static struct sysrq_key_op sysrq_showallcpus_op = {
    diff --git a/include/linux/nmi.h b/include/linux/nmi.h
    index 29af2d5..b752e80 100644
    --- a/include/linux/nmi.h
    +++ b/include/linux/nmi.h
    @@ -28,8 +28,23 @@ static inline void acpi_nmi_disable(void) { }
    static inline void acpi_nmi_enable(void) { }
    #endif

    -#ifndef trigger_all_cpu_backtrace
    -#define trigger_all_cpu_backtrace() do { } while (0)
    +/*
    + * Create trigger_all_cpu_backtrace() out of the arch-provided
    + * base function. Return whether such support was available,
    + * to allow calling code to fall back to some other mechanism:
    + */
    +#ifdef arch_trigger_all_cpu_backtrace
    +static inline bool trigger_all_cpu_backtrace(void)
    +{
    + arch_trigger_all_cpu_backtrace();
    +
    + return true;
    +}
    +#else
    +static inline bool trigger_all_cpu_backtrace(void)
    +{
    + return false;
    +}
    #endif

    #endif

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