Incorrect use of blocking ops in lirc_dev_fop_read

[Laura Abbott]

Hi,

We received a bug report 
(https://bugzilla.redhat.com/show_bug.cgi?id=1323440)

WARNING: CPU: 3 PID: 765 at kernel/sched/core.c:7557 
__might_sleep+0x75/0x80()
do not call blocking ops when !TASK_RUNNING; state=1 set at
[<ffffffffa03b2d31>] lirc_dev_fop_read+0x1e1/0x590 [lirc_dev]
CPU: 3 PID: 765 Comm: lircd Not tainted 4.4.5-300.fc23.x86_64+debug #1
Hardware name:                  /NUC5PPYB, BIOS
PYBSWCEL.86A.0031.2015.0601.1712 06/01/2015
 0000000000000286 00000000d9104369 ffff8801742bfc90 ffffffff8142b543
 ffff8801742bfcd8 ffffffff81c893ec ffff8801742bfcc8 ffffffff810aef42
 ffffffffa03b4428 00000000000002dc 0000000000000000 ffff88007640d380
Call Trace:
 [<ffffffff8142b543>] dump_stack+0x85/0xc2
 [<ffffffff810aef42>] warn_slowpath_common+0x82/0xc0
 [<ffffffff810aefdc>] warn_slowpath_fmt+0x5c/0x80
 [<ffffffff81885186>] ? _raw_spin_unlock_irqrestore+0x36/0x60
 [<ffffffffa03b2d31>] ? lirc_dev_fop_read+0x1e1/0x590 [lirc_dev]
 [<ffffffffa03b2d31>] ? lirc_dev_fop_read+0x1e1/0x590 [lirc_dev]
 [<ffffffff810dc475>] __might_sleep+0x75/0x80
 [<ffffffff8121bcd3>] __might_fault+0x43/0xa0
 [<ffffffffa03b2fe1>] lirc_dev_fop_read+0x491/0x590 [lirc_dev]
 [<ffffffff8110a38d>] ? trace_hardirqs_on+0xd/0x10
 [<ffffffff810e20f0>] ? wake_up_q+0x70/0x70
 [<ffffffff81276dc7>] __vfs_read+0x37/0x100
 [<ffffffff813a0963>] ? security_file_permission+0xa3/0xc0
 [<ffffffff812778d9>] vfs_read+0x89/0x130
 [<ffffffff81278658>] SyS_read+0x58/0xd0
 [<ffffffff81885b72>] entry_SYSCALL_64_fastpath+0x12/0x76

From looking at the code, it looks like the issue is that copy_to_user
may be called within the block of TASK_INTERRUPTIBLE. I don't know
the code well enough to try and propose a patch to fix this (I broke
code last time I tried to fix something like this)

Thanks,
Laura