[PATCH] Graceful failure in devfs_remove() in 2.5.x

[PATCH] Graceful failure in devfs_remove() in 2.5.x

[Pavel Roskin]

Hello!

It's already the second time that I encounter a kernel panic in the same
place.  When devfs_remove() is called on a non-existent file entry, the
kernel panics and I have to reboot the system.

First time it was unregistering of pseudoterminals.  This time it's
ide-floppy module that doesn't register devfs entries if the media is
absent but still tries to unregister them.  The bug in ide-floppy will be
reported separately.

The point of this message is that the failure in devfs_remove() is
possible, especially with rarely used drivers.  Secondly, is not fatal
enough to justify an immediate panic and reboot.  Thirdly, devfs misses a
chance to tell the user what's going wrong.

This patch makes devfs_remove() print an error to the kernel log and
continue.  PRINTK is defined in fs/devfs/base.c to report errors in the
cases like this one:

#define PRINTK(format, args...) \
   {printk (KERN_ERR "%s" format, __FUNCTION__ , ## args);}

The patch:

==============================================
--- linux.orig/fs/devfs/base.c
+++ linux/fs/devfs/base.c
@@ -1710,6 +1710,11 @@ void devfs_remove(const char *fmt, ...)
 	if (n < 64 && buf[0]) {
 		devfs_handle_t de = _devfs_find_entry(NULL, buf, 0);

+		if (!de) {
+			PRINTK ("(%s): not found, cannot remove\n", buf);
+			return;
+		}
+
 		write_lock(&de->parent->u.dir.lock);
 		_devfs_unregister(de->parent, de);
 		devfs_put(de);
==============================================

The patch is against Linux 2.5.70.

Linux 2.4.21-rc4 already has protection against panic although it doesn't
print the error message - see devfs_unlink() in fs/devfs/base.c

-- 
Regards,
Pavel Roskin

Re: [PATCH] Graceful failure in devfs_remove() in 2.5.x

[Christoph Hellwig]

On Tue, May 27, 2003 at 11:29:53AM -0400, Pavel Roskin wrote:
> This patch makes devfs_remove() print an error to the kernel log and
> continue.  PRINTK is defined in fs/devfs/base.c to report errors in the
> cases like this one:

Patch looks okay _except_ for use of this gross macro.  Just
ise plain printk instead.

Re: [PATCH] Graceful failure in devfs_remove() in 2.5.x

[Pavel Roskin]

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On Wed, 28 May 2003, Christoph Hellwig wrote:

> On Tue, May 27, 2003 at 11:29:53AM -0400, Pavel Roskin wrote:
> > This patch makes devfs_remove() print an error to the kernel log and
> > continue.  PRINTK is defined in fs/devfs/base.c to report errors in the
> > cases like this one:
>
> Patch looks okay _except_ for use of this gross macro.  Just
> ise plain printk instead.

I always try to follow the existing code style, but if you want me to make
an exception, here it is.  Fixed patch is attached.

-- 
Regards,
Pavel Roskin

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--- linux.orig/fs/devfs/base.c
+++ linux/fs/devfs/base.c
@@ -1710,6 +1710,12 @@ void devfs_remove(const char *fmt, ...)
 	if (n < 64 && buf[0]) {
 		devfs_handle_t de = _devfs_find_entry(NULL, buf, 0);
 
+		if (!de) {
+			printk(KERN_ERR "%s: %s not found, cannot remove\n",
+			       __FUNCTION__, buf);
+			return;
+		}
+
 		write_lock(&de->parent->u.dir.lock);
 		_devfs_unregister(de->parent, de);
 		devfs_put(de);