uio: uio_dmem_genirq: Fix missing unlock in irq configuration

In the Linux kernel, the following vulnerability has been resolved:

uio: uio_dmem_genirq: Fix missing unlock in irq configuration

Commit b74351287d4b ("uio: fix a sleep-in-atomic-context bug in
uio_dmem_genirq_irqcontrol()") started calling disable_irq() without
holding the spinlock because it can sleep. However, that fix introduced
another bug: if interrupt is already disabled and a new disable request
comes in, then the spinlock is not unlocked:

root@localhost:~# printf '\x00\x00\x00\x00' > /dev/uio0
root@localhost:~# printf '\x00\x00\x00\x00' > /dev/uio0
root@localhost:~# [ 14.851538] BUG: scheduling while atomic: bash/223/0x00000002
[ 14.851991] Modules linked in: uio_dmem_genirq uio myfpga(OE) bochs drm_vram_helper drm_ttm_helper ttm drm_kms_helper drm snd_pcm ppdev joydev psmouse snd_timer snd e1000fb_sys_fops syscopyarea parport sysfillrect soundcore sysimgblt input_leds pcspkr i2c_piix4 serio_raw floppy evbug qemu_fw_cfg mac_hid pata_acpi ip_tables x_tables autofs4 [last unloaded: parport_pc]
[ 14.854206] CPU: 0 PID: 223 Comm: bash Tainted: G OE 6.0.0-rc7 #21
[ 14.854786] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
[ 14.855664] Call Trace:
[ 14.855861] <TASK>
[ 14.856025] dump_stack_lvl+0x4d/0x67
[ 14.856325] dump_stack+0x14/0x1a
[ 14.856583] __schedule_bug.cold+0x4b/0x5c
[ 14.856915] __schedule+0xe81/0x13d0
[ 14.857199] ? idr_find+0x13/0x20
[ 14.857456] ? get_work_pool+0x2d/0x50
[ 14.857756] ? __flush_work+0x233/0x280
[ 14.858068] ? __schedule+0xa95/0x13d0
[ 14.858307] ? idr_find+0x13/0x20
[ 14.858519] ? get_work_pool+0x2d/0x50
[ 14.858798] schedule+0x6c/0x100
[ 14.859009] schedule_hrtimeout_range_clock+0xff/0x110
[ 14.859335] ? tty_write_room+0x1f/0x30
[ 14.859598] ? n_tty_poll+0x1ec/0x220
[ 14.859830] ? tty_ldisc_deref+0x1a/0x20
[ 14.860090] schedule_hrtimeout_range+0x17/0x20
[ 14.860373] do_select+0x596/0x840
[ 14.860627] ? __kernel_text_address+0x16/0x50
[ 14.860954] ? poll_freewait+0xb0/0xb0
[ 14.861235] ? poll_freewait+0xb0/0xb0
[ 14.861517] ? rpm_resume+0x49d/0x780
[ 14.861798] ? common_interrupt+0x59/0xa0
[ 14.862127] ? asm_common_interrupt+0x2b/0x40
[ 14.862511] ? __uart_start.isra.0+0x61/0x70
[ 14.862902] ? __check_object_size+0x61/0x280
[ 14.863255] core_sys_select+0x1c6/0x400
[ 14.863575] ? vfs_write+0x1c9/0x3d0
[ 14.863853] ? vfs_write+0x1c9/0x3d0
[ 14.864121] ? _copy_from_user+0x45/0x70
[ 14.864526] do_pselect.constprop.0+0xb3/0xf0
[ 14.864893] ? do_syscall_64+0x6d/0x90
[ 14.865228] ? do_syscall_64+0x6d/0x90
[ 14.865556] __x64_sys_pselect6+0x76/0xa0
[ 14.865906] do_syscall_64+0x60/0x90
[ 14.866214] ? syscall_exit_to_user_mode+0x2a/0x50
[ 14.866640] ? do_syscall_64+0x6d/0x90
[ 14.866972] ? do_syscall_64+0x6d/0x90
[ 14.867286] ? do_syscall_64+0x6d/0x90
[ 14.867626] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[...] stripped
[ 14.872959] </TASK>

('myfpga' is a simple 'uio_dmem_genirq' driver I wrote to test this)

The implementation of "uio_dmem_genirq" was based on "uio_pdrv_genirq" and
it is used in a similar manner to the "uio_pdrv_genirq" driver with respect
to interrupt configuration and handling. At the time "uio_dmem_genirq" was
introduced, both had the same implementation of the 'uio_info' handlers
irqcontrol() and handler(). Then commit 34cb27528398 ("UIO: Fix concurrency
issue"), which was only applied to "uio_pdrv_genirq", ended up making them
a little different. That commit, among other things, changed disable_irq()
to disable_irq_nosync() in the implementation of irqcontrol(). The
motivation there was to avoid a deadlock between irqcontrol() and
handler(), since it added a spinlock in the irq handler, and disable_irq()
waits for the completion of the irq handler.

By changing disable_irq() to disable_irq_nosync() in irqcontrol(), we also
avoid the sleeping-whil
---truncated---