[PATCH] reduce stack in cdrom/optcd.c

[PATCH] reduce stack in cdrom/optcd.c

[Randy.Dunlap]

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Hi,

This reduces stack usage in drivers/cdrom/optcd.c by
dynamically allocating a large (> 2 KB) buffer.

Patch is to 2.5.65.  Please apply.

~Randy

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patch_name:	optcdrom-stack.patch
patch_version:	2003-03-21.22:31:24
author:		Randy.Dunlap <rddunlap@osdl.org>
description:	reduce stack usage in drivers/cdrom/optcd::cdromread()
product:	Linux
product_versions: 2.5.65
changelog:	kmalloc() the large buffer
maintainer:	Leo Spiekman <leo@netlabs.net>
diffstat:	=
 drivers/cdrom/optcd.c |   22 +++++++++++++++++-----
 1 files changed, 17 insertions(+), 5 deletions(-)


diff -Naur ./drivers/cdrom/optcd.c%CDROM ./drivers/cdrom/optcd.c
--- ./drivers/cdrom/optcd.c%CDROM	Mon Mar 17 13:43:49 2003
+++ ./drivers/cdrom/optcd.c	Fri Mar 21 22:30:08 2003
@@ -1600,13 +1600,17 @@
 
 static int cdromread(unsigned long arg, int blocksize, int cmd)
 {
-	int status;
+	int status, ret = 0;
 	struct cdrom_msf msf;
-	char buf[CD_FRAMESIZE_RAWER];
+	char *buf;
 
 	if (copy_from_user(&msf, (void *) arg, sizeof msf))
 		return -EFAULT;
 
+	buf = kmalloc(CD_FRAMESIZE_RAWER, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
 	bin2bcd(&msf);
 	msf.cdmsf_min1 = 0;
 	msf.cdmsf_sec1 = 0;
@@ -1615,11 +1619,19 @@
 
 	DEBUG((DEBUG_VFS, "read cmd status 0x%x", status));
 
-	if (!sleep_flag_low(FL_DTEN, SLEEP_TIMEOUT))
-		return -EIO;
+	if (!sleep_flag_low(FL_DTEN, SLEEP_TIMEOUT)) {
+		ret = -EIO;
+		goto cdr_free;
+	}
+
 	fetch_data(buf, blocksize);
 
-	return copy_to_user((void *)arg, &buf, blocksize) ? -EFAULT : 0;
+	if (copy_to_user((void *)arg, &buf, blocksize))
+		ret = -EFAULT;
+
+cdr_free:
+	kfree(buf);
+	return ret;
 }
 
 

Re: [PATCH] reduce stack in cdrom/optcd.c

[Arjan van de Ven]

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On Sat, 2003-03-22 at 21:43, Alan Cox wrote:
> On Sat, 2003-03-22 at 06:51, Randy.Dunlap wrote:
> > Hi,
> > 
> > This reduces stack usage in drivers/cdrom/optcd.c by
> > dynamically allocating a large (> 2 KB) buffer.
> > 
> > Patch is to 2.5.65.  Please apply.
> 
> This loosk broken. You are using GFP_KERNEL memory allocations on the
> read path of a block device. What happens if the allocation fails 
> because we need memory

it's unlikely that you have your swap on the cdrom ;)

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Re: [PATCH] reduce stack in cdrom/optcd.c

[Alan Cox]

On Sat, 2003-03-22 at 06:51, Randy.Dunlap wrote:
> Hi,
> 
> This reduces stack usage in drivers/cdrom/optcd.c by
> dynamically allocating a large (> 2 KB) buffer.
> 
> Patch is to 2.5.65.  Please apply.

This loosk broken. You are using GFP_KERNEL memory allocations on the
read path of a block device. What happens if the allocation fails 
because we need memory

Surely that buffer needs to be allocated once at open and freed on close
?

Re: [PATCH] reduce stack in cdrom/optcd.c

[Jens Axboe]

On Sat, Mar 22 2003, Arjan van de Ven wrote:
> On Sat, 2003-03-22 at 21:43, Alan Cox wrote:
> > On Sat, 2003-03-22 at 06:51, Randy.Dunlap wrote:
> > > Hi,
> > > 
> > > This reduces stack usage in drivers/cdrom/optcd.c by
> > > dynamically allocating a large (> 2 KB) buffer.
> > > 
> > > Patch is to 2.5.65.  Please apply.
> > 
> > This loosk broken. You are using GFP_KERNEL memory allocations on the
> > read path of a block device. What happens if the allocation fails 
> > because we need memory
> 
> it's unlikely that you have your swap on the cdrom ;)

your swap device could still be plugged behind your cdrom.

-- 
Jens Axboe

Re: [PATCH] reduce stack in cdrom/optcd.c

[Randy.Dunlap]

On Tue, 25 Mar 2003 19:29:16 +0100 Jens Axboe <axboe@suse.de> wrote:

| On Sat, Mar 22 2003, Arjan van de Ven wrote:
| > On Sat, 2003-03-22 at 21:43, Alan Cox wrote:
| > > On Sat, 2003-03-22 at 06:51, Randy.Dunlap wrote:
| > > > Hi,
| > > > 
| > > > This reduces stack usage in drivers/cdrom/optcd.c by
| > > > dynamically allocating a large (> 2 KB) buffer.
| > > > 
| > > > Patch is to 2.5.65.  Please apply.
| > > 
| > > This loosk broken. You are using GFP_KERNEL memory allocations on the
| > > read path of a block device. What happens if the allocation fails 
| > > because we need memory
| > 
| > it's unlikely that you have your swap on the cdrom ;)
| 
| your swap device could still be plugged behind your cdrom.

I plan to change it as Alan suggested.  Will do.

--
~Randy

Re: [PATCH] reduce stack in cdrom/optcd.c

[Jens Axboe]

On Wed, Mar 26 2003, Randy.Dunlap wrote:
> 
> (resend; was lost last night)
> 
> 
> > From: Alan Cox <alan@lxorguk.ukuu.org.uk>
> > 
> > On Sat, 2003-03-22 at 06:51, Randy.Dunlap wrote:
> > > Hi,
> > > 
> > > This reduces stack usage in drivers/cdrom/optcd.c by
> > > dynamically allocating a large (> 2 KB) buffer.
> > > 
> > > Patch is to 2.5.65.  Please apply.
> > 
> > This loosk broken. You are using GFP_KERNEL memory allocations on the
> > read path of a block device. What happens if the allocation fails 
> > because we need memory
> > 
> > Surely that buffer needs to be allocated once at open and freed on close
> > ?
> > --
> 
> 
> Alan, Jens, anybody else-
> 
> Does this pass?

Yes, looks much better.

-- 
Jens Axboe

[PATCH] reduce stack in cdrom/optcd.c

[Randy.Dunlap]

(resend; was lost last night)


> From: Alan Cox <alan@lxorguk.ukuu.org.uk>
> 
> On Sat, 2003-03-22 at 06:51, Randy.Dunlap wrote:
> > Hi,
> > 
> > This reduces stack usage in drivers/cdrom/optcd.c by
> > dynamically allocating a large (> 2 KB) buffer.
> > 
> > Patch is to 2.5.65.  Please apply.
> 
> This loosk broken. You are using GFP_KERNEL memory allocations on the
> read path of a block device. What happens if the allocation fails 
> because we need memory
> 
> Surely that buffer needs to be allocated once at open and freed on close
> ?
> --


Alan, Jens, anybody else-

Does this pass?

Patch is now to 2.5.66.

Thanks,
~Randy


patch_name:	optcd-stackbuf.patch
patch_version:	2003-03-25.19:02:22
author:		Randy.Dunlap <rddunlap@osdl.org>
description:	pre-allocate readbuf instead of kmalloc() in cdromread();
		(previously modified for stack reduction)
product:	Linux
product_versions: 2.5.66
maintainer:	unknown (email bounces)
diffstat:	=
 drivers/cdrom/optcd.c |   37 +++++++++++++++++++------------------
 1 files changed, 19 insertions(+), 18 deletions(-)


diff -Naur ./drivers/cdrom/optcd.c%OPTCD ./drivers/cdrom/optcd.c
--- ./drivers/cdrom/optcd.c%OPTCD	2003-03-24 14:00:10.000000000 -0800
+++ ./drivers/cdrom/optcd.c	2003-03-25 19:01:06.000000000 -0800
@@ -1598,19 +1598,17 @@
 }
 
 
+static struct gendisk *optcd_disk;
+
+
 static int cdromread(unsigned long arg, int blocksize, int cmd)
 {
-	int status, ret = 0;
+	int status;
 	struct cdrom_msf msf;
-	char *buf;
 
 	if (copy_from_user(&msf, (void *) arg, sizeof msf))
 		return -EFAULT;
 
-	buf = kmalloc(CD_FRAMESIZE_RAWER, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
 	bin2bcd(&msf);
 	msf.cdmsf_min1 = 0;
 	msf.cdmsf_sec1 = 0;
@@ -1619,19 +1617,15 @@
 
 	DEBUG((DEBUG_VFS, "read cmd status 0x%x", status));
 
-	if (!sleep_flag_low(FL_DTEN, SLEEP_TIMEOUT)) {
-		ret = -EIO;
-		goto cdr_free;
-	}
+	if (!sleep_flag_low(FL_DTEN, SLEEP_TIMEOUT))
+		return -EIO;
 
-	fetch_data(buf, blocksize);
+	fetch_data(optcd_disk->private_data, blocksize);
 
-	if (copy_to_user((void *)arg, &buf, blocksize))
-		ret = -EFAULT;
+	if (copy_to_user((void *)arg, optcd_disk->private_data, blocksize))
+		return -EFAULT;
 
-cdr_free:
-	kfree(buf);
-	return ret;
+	return 0;
 }
 
 
@@ -1857,6 +1851,14 @@
 
 	if (!open_count && state == S_IDLE) {
 		int status;
+		char *buf;
+
+		buf = kmalloc(CD_FRAMESIZE_RAWER, GFP_KERNEL);
+		if (!buf) {
+			printk(KERN_INFO "optcd: cannot allocate read buffer\n");
+			return -ENOMEM;
+		}
+		optcd_disk->private_data = buf;		/* save read buffer */
 
 		toc_uptodate = 0;
 		opt_invalidate_buffers();
@@ -1922,6 +1924,7 @@
 			status = exec_cmd(COMOPEN);
 			DEBUG((DEBUG_VFS, "exec_cmd COMOPEN: %02x", -status));
 		}
+		kfree(optcd_disk->private_data);
 		del_timer(&delay_timer);
 		del_timer(&req_timer);
 	}
@@ -2010,8 +2013,6 @@
 
 #endif /* MODULE */
 
-static struct gendisk *optcd_disk;
-
 /* Test for presence of drive and initialize it. Called at boot time
    or during module initialisation. */
 static int __init optcd_init(void)


--
~Randy