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Subject[PATCH] irq_work: Fix IRQ_WORK_BUZY bit clearing
Date
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@intel.com>
Reported-by: Leonard Crestez <leonard.crestez@nxp.com>
Fixes: feb4a51323ba ("irq_work: Slightly simplify IRQ_WORK_PENDING clearing")
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
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
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