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:

quoted

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.