Re: Error returns not handled correctly by sysfs.c:subsys_attr_store()

On Wed, Nov 28, 2007 at 12:31:40PM -0700, Andrew Patterson wrote:
On Wed, 2007-11-28 at 16:42 +0900, Tejun Heo wrote:
Greg KH wrote:
On Mon, Nov 26, 2007 at 08:31:16PM -0800, Andrew Morton wrote:
On Wed, 21 Nov 2007 15:16:59 -0700 Andrew Patterson <andrew.patterson@xxxxxx> wrote:

The buf in fs/sysfs.c:subsys_attr_store() does not seem to be updated
correctly when returning a negative value (indicating that an error
condition has occurred) is returned. If a negative value is returned,
the next subsequent call to subsys_attr_store will have the contents of
buf appended to the previous call.
subsys_attr_store() gets deleted by
http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/gregkh-01-driver/kset-kill-subsys-attr.patch

So maybe we will soon accidentally fix whatever-this-is? Or maybe we will
faithfully maintain it.

Yes, subsys attributes go away, but this is showing a bug in the sysfs
core with attributes, not in the "middle" layers of attributes.

I bounced the original bug report to Tejun, who has been changing the
logic around this area to see if he sees anything that might be
different now.

Tejun?

Weird, the problem is not reproducible here.

# echo a > allow_restart
-bash: echo: write error: Invalid argument
[ 437.518024] buf_ptr = 0xffff810005e20000, buf = x
[ 437.518027] , count = 2
# echo b > allow_restart
-bash: echo: write error: Invalid argument
[ 438.972973] buf_ptr = 0xffff81001be6f000, buf = y
[ 438.972976] , count = 2
# echo c > allow_restart
-bash: echo: write error: Invalid argument
[ 440.539747] buf_ptr = 0xffff81001d4ba000, buf = z
[ 440.539750] , count = 2

Which is expected. On each open, sysfs_buffer is allocated with kzalloc
and the buffer is freed on close, so I don't see how it can happen.
Behavior for multiple write can be considered peculiar in that ppos is
essentially ignored and each write is passed just like brand new write
to ->store method but this too is the expected behavior.

# (echo a; echo b; echo c) > allow_restart
[ 765.257132] buf_ptr = 0xffff81001be4f000, buf = a
[ 765.257135] , count = 2
[ 765.285474] buf_ptr = 0xffff81001be4f000, buf = b
[ 765.285484] , count = 2
[ 765.314002] buf_ptr = 0xffff81001be4f000, buf = c
[ 765.314004] , count = 2
-bash: echo: write error: Invalid argument
-bash: echo: write error: Invalid argument
-bash: echo: write error: Invalid argument

Andrew Petterson, can you please build 2.6.24-rc3 from clean source tree
and retry?


I tried with clean 2.6.24-rc3 and get the same bad behavior. This is on
an ia64 box, so maybe that is an issue. I can try on an x86 box as well.

Please do so.

Oh, one other thing. I tried a "uname -r" to make sure I had the
correct kernel booted and got:

# uname -r
2.6.24-rc3
x
y
z

Heh, that's not good, try a clean tree :)

thanks,

greg k-h
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