Re: Contention on ->i_shared_lock in dup_mmap()

[Manfred Spraul <manfreds@colorfullife.com>]

Alexander Viro wrote:
> 
> OK, do_syslog() is just plain silly - it's resetting the buffer and code
> in question looks so:
>                 spin_lock_irq(&console_lock);
>                 logged_chars = 0;
>                 spin_unlock_irq(&console_lock);
> ... which is for all purposes equivalent to
>                 if (logged_chars) {
>                         ...
>                 }
> so this one is easy (looks like a klogd silliness).
> 
cpu0: do_syslog
	logged_chars = 0;

cpu1: printk()
	logged_chars++;

We really need the spinlock :-(

How many cpu's? How did you measure the contention?
I cannot imagine that do_syslog is really the source for the contention,
perhaps cpu0 was executing a slow console switch, and cpu1 called
do_syslog?

--
	Manfred
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