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SubjectRe: [PATCH] 2.4.16 kernel/printk.c (per processorinitializationcheck)

How hard would it be to fix that on ia64 code?

I'm really not willing to apply this kludge...


On Thu, 6 Dec 2001, Andrew Morton wrote:

> j-nomura@ce.jp.nec.com wrote:
> >
> > Hi,
> > excuse me for not prompt response. I've been off-line for 2 days.
> >
> > > > The reason I put it in release_console_sem() is that release_console_sem()
> > > > can be called from other functions than printk(), e.g. console_unblank().
> > > > I agree with you that it is clearer but I think it is not sufficient.
> > >
> > > I really doubt if any of those paths could be called before
> > > even the MMU is set up.
> >
>
> Marcelo,
>
> after a fairly lengthy off-list discussion, it turns out that
> special-casing printk is probably the best way to proceed
> to fix this one.
>
> The problem is that the boot processor sets up the console drivers,
> and is able to call them via printk(), but the application processors
> at that time are not able to call printk() because the console device
> driver mappings are not set up. Undoing this inside the ia64 boot code is
> complex and fragile. Possibly the problem exists on other platforms
> but hasn't been discovered yet.
>
> So the patch defines an architecture-specific macro `arch_consoles_callable()'
> which, if not defined, defaults to `1', so the impact to other platforms
> (and to uniprocessor ia64) is zero.
>
>
>
> --- linux-2.4.17-pre4/include/asm-ia64/system.h Thu Nov 22 23:02:59 2001
> +++ linux-akpm/include/asm-ia64/system.h Wed Dec 5 23:09:15 2001
> @@ -405,6 +405,10 @@ extern void ia64_load_extra (struct task
> ia64_psr(ia64_task_regs(prev))->dfh = 1; \
> __switch_to(prev,next,last); \
> } while (0)
> +
> +/* Return true if this CPU can call the console drivers in printk() */
> +#define arch_consoles_callable() (cpu_online_map & (1UL << smp_processor_id()))
> +
> #else
> # define switch_to(prev,next,last) do { \
> ia64_psr(ia64_task_regs(next))->dfh = (ia64_get_fpu_owner() != (next)); \
> --- linux-2.4.17-pre4/kernel/printk.c Thu Nov 22 23:02:59 2001
> +++ linux-akpm/kernel/printk.c Wed Dec 5 23:03:54 2001
> @@ -38,6 +38,10 @@
>
> #define LOG_BUF_MASK (LOG_BUF_LEN-1)
>
> +#ifndef arch_consoles_callable
> +#define arch_consoles_callable() (1)
> +#endif
> +
> /* printk's without a loglevel use this.. */
> #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
>
> @@ -438,6 +442,14 @@ asmlinkage int printk(const char *fmt, .
> log_level_unknown = 1;
> }
>
> + if (!arch_consoles_callable()) {
> + /*
> + * On some architectures, the consoles are not usable
> + * on secondary CPUs early in the boot process.
> + */
> + spin_unlock_irqrestore(&logbuf_lock, flags);
> + goto out;
> + }
> if (!down_trylock(&console_sem)) {
> /*
> * We own the drivers. We can drop the spinlock and let
> @@ -454,6 +466,7 @@ asmlinkage int printk(const char *fmt, .
> */
> spin_unlock_irqrestore(&logbuf_lock, flags);
> }
> +out:
> return printed_len;
> }
> EXPORT_SYMBOL(printk);
>

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