Messages in this thread | | | From | Dan Williams <> | Date | Thu, 16 Jul 2020 08:53:30 -0700 | Subject | Re: [PATCH] /dev/mem: Add missing memory barriers for devmem_inode |
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On Wed, Jul 15, 2020 at 11:07 PM Eric Biggers <ebiggers@kernel.org> wrote: > > From: Eric Biggers <ebiggers@google.com> > > WRITE_ONCE() isn't the correct way to publish a pointer to a data > structure, since it doesn't include a write memory barrier. Therefore > other tasks may see that the pointer has been set but not see that the > pointed-to memory has finished being initialized yet. Instead a > primitive with "release" semantics is needed. > > Use smp_store_release() for this. > > The use of READ_ONCE() on the read side is still potentially correct if > there's no control dependency, i.e. if all memory being "published" is > transitively reachable via the pointer itself. But this pairing is > somewhat confusing and error-prone. So just upgrade the read side to > smp_load_acquire() so that it clearly pairs with smp_store_release(). > > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Kees Cook <keescook@chromium.org> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Russell King <linux@arm.linux.org.uk> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Fixes: 3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims the region") > Signed-off-by: Eric Biggers <ebiggers@google.com>
Makes sense:
Acked-by: Dan Williams <dan.j.williams@intel.com>
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