Re: [PATCH] irq_work: Fix IRQ_WORK_BUZY bit clearing

[Naresh Kamboju]

Hi Frederic,

Thanks for this fix patch.

On Thu, 14 Nov 2019 at 21:26, Leonard Crestez <leonard.crestez@xxxxxxx> wrote:
>
> On 13.11.2019 19:12, Frederic Weisbecker wrote:
> > 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.
>
> Busy is spelled with an S
>
> >
> > 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> everywhere.
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>
> Tested-by: Leonard Crestez <leonard.crestez@xxxxxxx>
>
> Without this patch switching cpufreq governors hangs on arm64.

Right.

This patch solved two problems,
1) juno-r2 boot pass now
2) rcu_sched self-detected stall on CPU on x86_64 problem is solved now.

Tested-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>

Hope this will get merged into linux next.

ref:
https://lkft.validation.linaro.org/scheduler/job/1010542#L260
https://lkft.validation.linaro.org/scheduler/job/1010793#L493

- Naresh