On Wed, May 20, 2020 at 06:35:25PM -0700, Dan Williams wrote:
> +static struct inode *devmem_inode;
> +
> +#ifdef CONFIG_IO_STRICT_DEVMEM
> +void revoke_devmem(struct resource *res)
> +{
> + struct inode *inode = READ_ONCE(devmem_inode);
> +
> + /*
> + * Check that the initialization has completed. Losing the race
> + * is ok because it means drivers are claiming resources before
> + * the fs_initcall level of init and prevent /dev/mem from
> + * establishing mappings.
> + */
> + smp_rmb();
> + if (!inode)
> + return;
But we don't need the smp_rmb() here, right? READ_ONCE and WRITE_ONCE
are a DATA DEPENDENCY barrier (in Documentation/memory-barriers.txt parlance)
so the smp_rmb() is superfluous ...
> + /*
> + * Use a unified address space to have a single point to manage
> + * revocations when drivers want to take over a /dev/mem mapped
> + * range.
> + */
> + inode->i_mapping = devmem_inode->i_mapping;
> + inode->i_mapping->host = devmem_inode;
umm ... devmem_inode->i_mapping->host doesn't already point to devmem_inode?
> +
> + /* publish /dev/mem initialized */
> + smp_wmb();
> + WRITE_ONCE(devmem_inode, inode);
As above, unnecessary barrier, I think.
