[PATCH] irq_work: Fix IRQ_WORK_BUZY bit clearing

[Frederic Weisbecker]

While attempting to clear the buzy bit at the end of a work execution,
atomic_cmpxchg() expects the value of the flags with the pending bit
cleared as the old value. However we are passing by mistake the value of
the flags before we actually cleared the pending bit.

As a result, clearing the buzy bit fails and irq_work_sync() may stall:

	watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [blktrace:4948]
	CPU: 0 PID: 4948 Comm: blktrace Not tainted 5.4.0-rc7-00003-gfeb4a51323bab #1
	Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
	RIP: 0010:irq_work_sync+0x4/0x10
	Call Trace:
	  relay_close_buf+0x19/0x50
	  relay_close+0x64/0x100
	  blk_trace_free+0x1f/0x50
	  __blk_trace_remove+0x1e/0x30
	  blk_trace_ioctl+0x11b/0x140
	  blkdev_ioctl+0x6c1/0xa40
	  block_ioctl+0x39/0x40
	  do_vfs_ioctl+0xa5/0x700
	  ksys_ioctl+0x70/0x80
	  __x64_sys_ioctl+0x16/0x20
	  do_syscall_64+0x5b/0x1d0
	  entry_SYSCALL_64_after_hwframe+0x44/0xa9

So clear the appropriate bit before passing the old flags to cmpxchg().

Reported-by: kernel test robot <rong.a.chen@xxxxxxxxx>
Reported-by: Leonard Crestez <leonard.crestez@xxxxxxx>
Fixes: feb4a51323ba ("irq_work: Slightly simplify IRQ_WORK_PENDING clearing")
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Paul E . McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/irq_work.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 49c53f80a13a..828cc30774bc 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -158,6 +158,7 @@ static void irq_work_run_list(struct llist_head *list)
 		 * Clear the BUSY bit and return to the free state if
 		 * no-one else claimed it meanwhile.
 		 */
+		flags &= ~IRQ_WORK_PENDING;
 		(void)atomic_cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
 	}
 }
-- 
2.23.0