Re: [PATCH 1/2] NFSv4.1: Again fix a race where CB_NOTIFY_LOCK fails to wake a waiter

[Greg KH <greg@kroah.com>]

On Wed, May 08, 2019 at 05:13:25PM +0800, Yihao Wu wrote:
> Commit b7dbcc0e433f ""NFSv4.1: Fix a race where CB_NOTIFY_LOCK fails
> to wake a waiter" found this bug. However it didn't fix it. This can
> be fixed by adding memory barrier pair.
> 
> Specifically, if any CB_NOTIFY_LOCK should be handled between unlocking
> the wait queue and freezable_schedule_timeout, only two cases are
> possible. So CB_NOTIFY_LOCK will not be dropped unexpectly.
> 
> 1. The callback thread marks the NFS client as waked. Then NFS client
> noticed that itself is waked, so it don't goes to sleep. And it cleans
> its wake mark.
> 
> 2. The NFS client noticed that itself is not waked yet, so it goes to
> sleep. No modification will ever happen to the wake mark in between.
> 
> Fixes: a1d617d ("nfs: allow blocking locks to be awoken by lock callbacks")
> Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
> ---
>  fs/nfs/nfs4proc.c | 21 +++++----------------
>  1 file changed, 5 insertions(+), 16 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>