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Subject[tip: irq/core] irq_work: Fix IRQ_WORK_BUSY bit clearing
The following commit has been merged into the irq/core branch of tip:

Commit-ID: e9838bd51169af87ae248336d4c3fc59184a0e46
Gitweb: https://git.kernel.org/tip/e9838bd51169af87ae248336d4c3fc59184a0e46
Author: Frederic Weisbecker <frederic@kernel.org>
AuthorDate: Wed, 13 Nov 2019 18:12:01 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 15 Nov 2019 10:48:37 +01:00

irq_work: Fix IRQ_WORK_BUSY bit clearing

While attempting to clear the busy 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 by mistake the value of the flags is
passed without clearing the pending bit first.

As a result, clearing the busy 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
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().

Fixes: feb4a51323ba ("irq_work: Slightly simplify IRQ_WORK_PENDING clearing")
Reported-by: kernel test robot <rong.a.chen@intel.com>
Reported-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Leonard Crestez <leonard.crestez@nxp.com>
Link: https://lkml.kernel.org/r/20191113171201.14032-1-frederic@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 49c53f8..828cc30 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);
}
}
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