linux-kernel - Re: [PATCH] Reduce __print_symbol/sprint

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Date:	Fri, 21 Sep 2007 14:45:37 +0200
From:	Gilboa Davara <gilboad@...il.com>
To:	Paulo Marques <pmarques@...popie.com>
Cc:	Satyam Sharma <satyam@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Reduce __print_symbol/sprint_symbol stack usage.

Hello Paulo,

[snip]
> I must say I agree with Satyam here.
> 
> Locking in the panic path might leave us without some critical debug 
> information, which is much more important than all this.
> 
> Maybe it would be better to change the print_symbol interface to avoid 
> having a "char buffer[KSYM_SYMBOL_LEN];" at all.
> 
> Most print_symbol callers use something like "yada yada %s" as the 
> format string, with an optional "\n" in the end.
> 
> if we change the interface from "print_symbol(fmt, addr)" to 
> "print_symbol(prefix, addr, int newline)" we can simply do:
> 
> printk(prefix);
> printk_symbol(addr);
> if (newline)
> 	printk("\n");
> 
> where "printk_symbol" is a new function that does the same as 
> sprint_symbol, but does "printk" instead of "sprintf".
> 
> This should reduce immensely the stack usage of print_symbol without the 
> need for locking.

I fully agree.
... Further more, multiple printk_symbols should be combined into a
single, multi-line printk transaction. (To prevent debug printk's from
trashing a BUG() dump_stack). 

> 
> Of course this requires changing _all_ callers of print_symbol to use 
> the new interface, but these are less than 100 ;)

This is my first contribution to the Linux kernel. As such I rather
start small, and work my way up slowly. (Read: solve the immediate stack
over-run now, think about changing the symbol_display interface later)

> 
> Comments?

I do agree that the current interface needs work.

... But as I said, I rather start slowly and on small scale. (Though I
did find a rather problematic place to start at... ;))

- Gilboa

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