Re: writing to sysfs appears to hang

[Jens Axboe <axboe@suse.de>]

On Fri, Nov 15 2002, Mike Anderson wrote:
> Paul Larson [plars@linuxtestproject.org] wrote:
> > I've been playing with sysfs and notices something odd.  If I do this:
> > echo 1 > /sys/devices/sys/name
> > the process appears to be hung.  ^c won't return control to me.  If I
> > log in on another console though, I can't find it running in the process
> > list.  All I can do is kill the login process.  No kernel errors when I
> > do this, just the hung terminal.
> > 
> > -Paul Larson
> 
> I repeated your example and in a quick look at the backtrace
> the echo is in a loop calling down into sysfs_write_file/dev_attr_store.
> 
> I think the problem is that if a device does not have a attribute store
> function the return value from dev_attr_store is incorrect.

This has been in the deadline-rbtree patches for some time (uses writes
to sysfs, too).

===== fs/sysfs/inode.c 1.59 vs edited =====
--- 1.59/fs/sysfs/inode.c	Wed Oct 30 21:27:35 2002
+++ edited/fs/sysfs/inode.c	Fri Nov  8 14:33:59 2002
@@ -243,7 +243,7 @@
 	if (kobj && kobj->subsys)
 		ops = kobj->subsys->sysfs_ops;
 	if (!ops || !ops->store)
-		return 0;
+		return -EINVAL;
 
 	page = (char *)__get_free_page(GFP_KERNEL);
 	if (!page)


-- 
Jens Axboe