linux-kernel - Re: [PATCH] Reduce stack used by lib/hexdump.c

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Date:	Wed, 5 Dec 2007 23:10:40 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kyle Moffett <mrmacman_g4@....com>
Cc:	Joe Perches <joe@...ches.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	jengelh@...putergmbh.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Reduce stack used by lib/hexdump.c

On Thu, 6 Dec 2007 00:58:38 -0500 Kyle Moffett <mrmacman_g4@....com> wrote:

> On Dec 05, 2007, at 21:42:35, Joe Perches wrote:
> > On Wed, 2007-12-05 at 18:18 -0800, Randy Dunlap wrote:
> >> Joe Perches wrote:
> >>> Maybe just eliminate the 16 or 32 byte width option and force it  
> >>> to only 16 byte widths.
> >> Have you checked users (callers)?  I'm pretty sure that one of the  
> >> callers wanted 32 and that's why it's there.
> >
> > I did.  There is only 1 subsystem.  That's easy to change.
> >
> > drivers/mtd/ubi/debug.c:  print_hex_dump(KERN_DEBUG, "",  
> > DUMP_PREFIX_OFFSET, 32, 1,
> > drivers/mtd/ubi/io.c:     print_hex_dump(KERN_DEBUG, "",  
> > DUMP_PREFIX_OFFSET, 32, 1,
> >
> > Long lines in the log file are not too easy to read anyway.  Using  
> > 16 byte dumps per line instead of 32 isn't painful.
> >
> > It gets rid of the allocation, reduces the argument count and makes  
> > the kernel smaller.  I think it's all good.
> >
> > Every current caller would have to change though.
> 
> Alternatively, since print_hex_dump is not a performance-critical  
> path (and usually indicates an error/debug condition), you could  
> probably just make a static "hexdump_lock" spinlock and  
> spin_lock_irqsave()/spin_unlock_irqrestore().  It would always nest  
> inside any other lock (except during crash, where we break locks  
> already for printk()), and I doubt any of the callers would notice  
> the serialization since they're already serialized on the printk buffer.
> 

Yup, that'd work.
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