From: "Randy.Dunlap" <rddunlap@osdl.org>
To: Jeff Garzik <jgarzik@pobox.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: top stack (l)users for 2.5.69
Date: Wed, 7 May 2003 13:38:56 -0700 [thread overview]
Message-ID: <20030507133856.02748f4e.rddunlap@osdl.org> (raw)
In-Reply-To: <3EB95BD7.8060700@pobox.com>
On Wed, 07 May 2003 15:17:43 -0400 Jeff Garzik <jgarzik@pobox.com> wrote:
| Linus Torvalds wrote:
| > In article <Pine.LNX.4.53.0305070933450.11740@chaos>,
| > Richard B. Johnson <root@chaos.analogic.com> wrote:
| >
| >>You know (I hope) that allocating stuff on the stack is not
| >>"bad".
| >
| >
| > Allocating stuff on the stack _is_ bad if you allocate more than a few
| > hundred bytes. That's _especially_ true deep down in the call-sequence,
| > ie in device drivers, low-level filesystems etc.
| >
| > The kernel stack is a very limited resource, with no protection from
| > overflow. Being lazy and using automatic variables is a BAD BAD thing,
| > even if it's syntactically easy and generates good code.
|
|
| Note that the problem is exacerbated if you have a bunch of disjoint
| stack scopes. For that case, gcc will take the _sum_ of the stacks and
| not the union. rth was kind enough to file gcc PR 9997 on this problem.
Glad to hear that.
| It is turning out to be fairly common problem in the various drivers'
| ioctl handlers. Kernel hackers (myself included) often create automatic
| variables for each case in a C switch statement. (and now I'm having to
| go back and fix that :))
I've written a few of the stack reduction patches. Lots of ioctl functions
need work, so gcc handling it better would be good to have.
I have mostly used kmalloc/kfree, but using automatic variables is certainly
cleaner to write (code). One of the patches that I did just made each ioctl
cmd call a separate function, and then each separate function was able to use
automatic variables on the stack instead of kmalloc/kfree. I prefer this
method when it's feasible (and until gcc can handle these cases).
--
~Randy
next prev parent reply other threads:[~2003-05-07 20:29 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-07 13:20 top stack (l)users for 2.5.69 Jörn Engel
2003-05-07 13:45 ` Richard B. Johnson
2003-05-07 13:56 ` Jörn Engel
2003-05-07 14:16 ` Richard B. Johnson
2003-05-07 17:13 ` Jonathan Lundell
2003-05-07 17:40 ` Richard B. Johnson
2003-05-07 18:12 ` Roland Dreier
2003-05-07 18:28 ` Richard B. Johnson
2003-05-07 18:44 ` Timothy Miller
2003-05-07 18:46 ` Roland Dreier
2003-05-07 19:30 ` Richard B. Johnson
2003-05-07 19:42 ` Roland Dreier
2003-05-07 20:04 ` Richard B. Johnson
2003-05-07 20:23 ` Roland Dreier
2003-05-07 20:42 ` Timothy Miller
2003-05-08 9:06 ` Jörn Engel
2003-05-08 11:33 ` Richard B. Johnson
2003-05-08 12:00 ` Helge Hafting
2003-05-08 15:42 ` Timothy Miller
2003-05-09 8:57 ` Miles Bader
2003-05-09 16:50 ` Timothy Miller
2003-05-08 16:47 ` Davide Libenzi
2003-05-07 18:51 ` Davide Libenzi
2003-05-07 19:22 ` Richard B. Johnson
2003-05-07 19:31 ` Davide Libenzi
2003-05-07 19:39 ` Hua Zhong
2003-05-07 21:47 ` Martin J. Bligh
2003-05-08 10:29 ` David Howells
2003-05-07 17:55 ` Jörn Engel
2003-05-07 16:20 ` Martin J. Bligh
2003-05-07 19:01 ` Dave Hansen
2003-05-07 20:06 ` Jörn Engel
2003-05-07 20:14 ` Dave Hansen
2003-05-08 8:41 ` Jörn Engel
2003-05-08 16:51 ` Dave Hansen
2003-05-08 22:12 ` Jörn Engel
2003-05-07 21:30 ` Jesse Pollard
2003-05-07 21:54 ` Timothy Miller
2003-05-07 22:01 ` Jesse Pollard
2003-05-07 14:33 ` Torsten Landschoff
2003-05-07 14:47 ` William Lee Irwin III
2003-05-07 15:04 ` Torsten Landschoff
2003-05-07 16:01 ` William Lee Irwin III
2003-05-08 15:36 ` Ingo Oeser
2003-05-08 18:04 ` William Lee Irwin III
2003-05-07 15:23 ` Timothy Miller
2003-05-07 15:47 ` William Lee Irwin III
2003-05-07 16:49 ` Jörn Engel
2003-05-07 17:18 ` Davide Libenzi
2003-05-07 17:40 ` Jörn Engel
2003-05-07 18:35 ` Davide Libenzi
2003-05-07 19:45 ` Jörn Engel
2003-05-07 18:23 ` William Lee Irwin III
2003-05-07 17:38 ` William Lee Irwin III
2003-05-07 17:47 ` Jörn Engel
2003-05-07 14:49 ` Richard B. Johnson
2003-05-07 18:36 ` Linus Torvalds
2003-05-07 19:17 ` Jeff Garzik
2003-05-07 20:38 ` Randy.Dunlap [this message]
2003-05-07 21:27 ` Marcus Alanen
2003-05-07 21:27 ` Randy.Dunlap
2003-05-08 15:10 ` Ingo Oeser
2003-05-08 17:12 ` Randy.Dunlap
2003-05-07 19:38 Chuck Ebbert
2003-05-08 14:08 Chuck Ebbert
2003-05-08 18:04 ` Jonathan Lundell
2003-05-08 19:05 ` Timothy Miller
2003-05-08 21:00 ` Jonathan Lundell
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