From: Matthew Wilcox <willy@infradead.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: gregkh@linuxfoundation.org, Arnd Bergmann <arnd@arndb.de>,
Ingo Molnar <mingo@redhat.com>, Kees Cook <keescook@chromium.org>,
Russell King <linux@arm.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3] /dev/mem: Revoke mappings when a driver claims the region
Date: Wed, 20 May 2020 19:26:28 -0700 [thread overview]
Message-ID: <20200521022628.GE16070@bombadil.infradead.org> (raw)
In-Reply-To: <159002475918.686697.11844615159862491335.stgit@dwillia2-desk3.amr.corp.intel.com>
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.
next prev parent reply other threads:[~2020-05-21 2:26 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-21 1:35 [PATCH v3] /dev/mem: Revoke mappings when a driver claims the region Dan Williams
2020-05-21 2:26 ` Matthew Wilcox [this message]
2020-05-21 4:37 ` Dan Williams
2020-05-21 4:39 ` Dan Williams
2020-05-21 11:41 ` Matthew Wilcox
2020-05-21 18:21 ` Dan Williams
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