[PATCH 1/3] uio: uio_dmem_genirq: Fix missing unlock in irq configuration

[Rafael Mendonca]

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-while-atomic bug that commit b74351287d4b ("uio: fix a
sleep-in-atomic-context bug in uio_dmem_genirq_irqcontrol()") was trying to
fix. Thus, this fixes the missing unlock in irqcontrol() by importing the
implementation of irqcontrol() handler from the "uio_pdrv_genirq" driver.
In the end, it reverts commit b74351287d4b ("uio: fix a
sleep-in-atomic-context bug in uio_dmem_genirq_irqcontrol()") and change
disable_irq() to disable_irq_nosync().

It is worth noting that this still does not address the concurrency issue
fixed by commit 34cb27528398 ("UIO: Fix concurrency issue"). It will be
addressed separately in the next commits.

Split out from commit 34cb27528398 ("UIO: Fix concurrency issue").

Fixes: b74351287d4b ("uio: fix a sleep-in-atomic-context bug in uio_dmem_genirq_irqcontrol()")
Signed-off-by: Rafael Mendonca <rafaelmendsr@xxxxxxxxx>
---
 drivers/uio/uio_dmem_genirq.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/uio/uio_dmem_genirq.c b/drivers/uio/uio_dmem_genirq.c
index 1106f3376404..cb283ee36eaa 100644
--- a/drivers/uio/uio_dmem_genirq.c
+++ b/drivers/uio/uio_dmem_genirq.c
@@ -132,13 +132,11 @@ static int uio_dmem_genirq_irqcontrol(struct uio_info *dev_info, s32 irq_on)
 	if (irq_on) {
 		if (test_and_clear_bit(0, &priv->flags))
 			enable_irq(dev_info->irq);
-		spin_unlock_irqrestore(&priv->lock, flags);
 	} else {
-		if (!test_and_set_bit(0, &priv->flags)) {
-			spin_unlock_irqrestore(&priv->lock, flags);
-			disable_irq(dev_info->irq);
-		}
+		if (!test_and_set_bit(0, &priv->flags))
+			disable_irq_nosync(dev_info->irq);
 	}
+	spin_unlock_irqrestore(&priv->lock, flags);
 
 	return 0;
 }
-- 
2.34.1