Re: [PATCH] Input: Use for_each_set_bit where appropriate

[Stephen Chandler Paul <cpaul@redhat.com>]

On Sat, 2015-09-19 at 11:26 -0700, Dmitry Torokhov wrote:
> On Thu, Sep 17, 2015 at 04:02:47PM -0400, Stephen Chandler Paul
> wrote:
> > Hi! The currently upstream version of this patch actually breaks
> > uinput, and causes the kernel to panic when attempting to run it
> > under
> > qemu using spice. Here's a backtrace from kdb:
> > 
> > Stack traceback for pid 656
> > 0xffff8800babed480      656        1  1    2   R 
> >  0xffff8800babefa80 *spice-vdagentd
> >  ffff88013747bd58 0000000000000018 ffff88013747bd80
> > ffff8800b7977000
> >  0000000000000003 0000000000000001 0000000000000001
> > ffff8800b7977240
> >  ffff88013747bdc0 ffffffff8163f449 0000000000000286
> > 0000000000000018
> > Call Trace:
> >  [<ffffffff8163f449>] ? input_event+0x59/0x80
> >  [<ffffffffa0509234>] ? uinput_write+0x154/0x460 [uinput]
> >  [<ffffffffa00e704d>] ? port_fops_read+0xfd/0x1f0 [virtio_console]
> >  [<ffffffff81261627>] ? __vfs_write+0x37/0x100
> >  [<ffffffff81261ff9>] ? vfs_write+0xa9/0x1a0
> >  [<ffffffff81283386>] ? __fget_light+0x66/0x90
> >  [<ffffffff81262cf8>] ? SyS_write+0x58/0xd0
> >  [<ffffffff81833c72>] ? entry_SYSCALL_64_fastpath+0x12/0x76
> > 
> > And the relevant messages from dmesg:
> > 
> > <1>[   15.064330] BUG: unable to handle kernel NULL pointer
> > dereference at 0000000000000024
> > <1>[   15.064336] IP: [<ffffffff8163f142>]
> > input_handle_event+0x232/0x4e0
> > <4>[   15.064343] PGD 0 
> > <4>[   15.064345] Oops: 0000 [#1] SMP
> > 
> > The steps for reproducing this are pretty simple: setup a Fedora 22
> > VM,
> > build the latest kernel and install it with make install, and try
> > to
> > boot the machine and use it over spice with qemu. After moving the
> > cursor it'll run into a NULL dereference and panic.
> > 
> > I've tested reverting this commit, and that fixes the NULL
> > dereference
> > completely. I'm willing to git send-email you the revert if wish.
> 
> *sigh* Sorry about that, the 2nd chunk of the change was completely
> bogus.
> 
> Does the patch below fixes this for you?
Yep! Applied it to my local tree, and the virtual machine appears to
have no issues now.

Cheers,
	Lyude

> 
> Thanks.
>