[Xen-devel] Re: [PATCH] xen: debugging aid to track those who have disabled preemption

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

This is obviously a bit skanky but I figured it might be useful to
others in the future even if it never gets further than the list
archive.

Ian.

On Mon, 2011-01-17 at 14:15 +0000, Ian Campbell wrote:
> # HG changeset patch
> # User Ian Campbell <ian.campbell@xxxxxxxxxx>
> # Date 1295273570 0
> # Node ID 15e53a2463f084c3adbbb21b4deb30d0d4f79b45
> # Parent  711cbaa038cae8c03cf825165d2e07b0a3c94f89
> xen: debugging aid to track those who have disabled preemption.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> 
> diff -r 711cbaa038ca -r 15e53a2463f0 xen/common/preempt.c
> --- a/xen/common/preempt.c    Mon Jan 17 14:12:48 2011 +0000
> +++ b/xen/common/preempt.c    Mon Jan 17 14:12:50 2011 +0000
> @@ -21,5 +21,48 @@
>   */
>  
>  #include <xen/preempt.h>
> +#include <xen/symbols.h>
>  
>  DEFINE_PER_CPU(unsigned int, __preempt_count);
> +
> +#ifdef DEBUG_PREEMPT
> +
> +#define NR_PREEMPT_DEBUG 16
> +
> +struct preempt_info {
> +     const char *file;
> +     unsigned long line;
> +     const char *func;
> +     unsigned long r0, r1;
> +};
> +typedef struct preempt_info preempt_info_t[NR_PREEMPT_DEBUG];
> +
> +DEFINE_PER_CPU(preempt_info_t, __preempt_debug);
> +
> +void preempt_debug(const char *file, const unsigned long line, const char 
> *func)
> +{
> +     struct preempt_info *pi = &this_cpu(__preempt_debug)[preempt_count()];
> +     if (preempt_count() >= NR_PREEMPT_DEBUG)
> +             return;
> +     pi->file = file;
> +     pi->func = func;
> +     pi->line = line;
> +     pi->r0 = (unsigned long)__builtin_return_address(0);
> +     pi->r1 = (unsigned long)__builtin_return_address(1);
> +}
> +
> +void preempt_debug_dump(void)
> +{
> +     struct preempt_info *pi = this_cpu(__preempt_debug);
> +     int i, count = preempt_count();
> +
> +     printk("preempt debug on CPU%d, count %d:\n", smp_processor_id(), 
> count);
> +     count = min(count, NR_PREEMPT_DEBUG);
> +     for(i=0;i<count;i++, pi++) {
> +             printk("%d @ 0x%p\n", i, pi);
> +             printk("  %s %s:%ld\n", pi->func, pi->file, pi->line);
> +             printk("  %#lx", pi->r0); print_symbol(" %s\n", pi->r0);
> +             printk("  %#lx", pi->r1); print_symbol(" %s\n", pi->r1);
> +     }
> +}
> +#endif
> diff -r 711cbaa038ca -r 15e53a2463f0 xen/drivers/char/console.c
> --- a/xen/drivers/char/console.c      Mon Jan 17 14:12:48 2011 +0000
> +++ b/xen/drivers/char/console.c      Mon Jan 17 14:12:50 2011 +0000
> @@ -961,6 +961,7 @@ void panic(const char *fmt, ...)
>      printk("Panic on CPU %d:\n", smp_processor_id());
>      printk("%s", buf);
>      printk("****************************************\n\n");
> +    preempt_debug_dump();
>      if ( opt_noreboot )
>          printk("Manual reset required ('noreboot' specified)\n");
>      else
> diff -r 711cbaa038ca -r 15e53a2463f0 xen/include/xen/preempt.h
> --- a/xen/include/xen/preempt.h       Mon Jan 17 14:12:48 2011 +0000
> +++ b/xen/include/xen/preempt.h       Mon Jan 17 14:12:50 2011 +0000
> @@ -18,7 +18,18 @@ DECLARE_PER_CPU(unsigned int, __preempt_
>  
>  #define preempt_count() (this_cpu(__preempt_count))
>  
> +//#define DEBUG_PREEMPT
> +
> +#ifdef DEBUG_PREEMPT
> +extern void preempt_debug(const char *file, const unsigned long line, const 
> char *func);
> +extern void preempt_debug_dump(void);
> +#else
> +static inline void preempt_debug(const char *file, const unsigned long line, 
> const char *func) {}
> +static inline void preempt_debug_dump(void) {}
> +#endif
> +
>  #define preempt_disable() do {                  \
> +    preempt_debug(__FILE__, __LINE__, __func__);\
>      preempt_count()++;                          \
>      barrier();                                  \
>  } while (0)



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