[PATCH v2 2/2] fscache: Add the missing smp_mb__after_atomic() before wake_up_bit()

[Hou Tao]

Hi,

On 1/12/2023 12:09 AM, David Howells wrote:
> Hou Tao <houtao at huaweicloud.com> wrote:
>
>> fscache_create_volume_work() uses wake_up_bit() to wake up the processes
>> which are waiting for the completion of volume creation. According to
>> comments in wake_up_bit() and waitqueue_active(), an extra smp_mb() is
>> needed to guarantee the memory order between FSCACHE_VOLUME_CREATING
>> flag and waitqueue_active() before invoking wake_up_bit().
> What two values are you ordering?
>
> If we're using this to create a critical section, then yes, we would need a
> barrier to order the changes inside the critical section before changing the
> memory location that forms the lock - but this is not a critical section.
It is similar with patch #1. The smp_mb() is used for order between
volume->flags and wq->head.
> David
>