Messages in this thread | | | Date | Thu, 9 Jun 2011 15:55:42 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/3] printk: Avoid all wakeups from printk |
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* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> +static void __console_flush(void);
I'd suggest moving this function to the right place, so that no prototypes are necessary.
> +/* > + * Special 'atomic' semaphore operations that mimmick down_trylock() + up(),
mimic
> + * except they don't release the semaphore internal lock and optimize the > + * sem->count fiddling away. > + * > + * The advantage is that this construct doesn't generate wakeups on atomic_up() > + * since any contending semaphore acuiqisition will still be spinning on the
acquisition.
> + * internal lock, instead of having gotten queued on the wait_list. > + * > + * printk() uses this to avoid generating wakeups, which would make it unsafe > + * to use in certain contexts (avoids lock inversion or lock recursion with > + * the scheduler locks). > + * > + * Assumes IRQs are disabled.
I'd add:
* Note: We emphatically do *not* want this function exported. Ever.
and maybe:
* Note2: Even asking for that will likely buy you a nasty response.
> + */ > +static int atomic_down_trylock(struct semaphore *sem) > +{ > + spin_lock(&sem->lock); > + if (sem->count > 0) > + return 0; > + > + spin_unlock(&sem->lock); > + return 1; > +} > + > +static void atomic_up(struct semaphore *sem) > +{ > + spin_unlock(&sem->lock); > +} > + > asmlinkage int vprintk(const char *fmt, va_list args) > { > int printed_len = 0; > @@ -943,19 +939,14 @@ asmlinkage int vprintk(const char *fmt, > if (*p == '\n') > new_text_line = 1; > } > + printk_cpu = UINT_MAX; > + spin_unlock(&logbuf_lock);
Hm, is that printk_cpu setting inside the critical section safe? What happens if we get an NMI on this CPU in that window?
Thanks,
Ingo
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