• Mark Rutland's avatar
    locking/atomics, selftests/powerpc: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE() · 564cbc87
    Mark Rutland authored
    For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
    preference to ACCESS_ONCE(), and new code is expected to use one of the
    former. So far, there's been no reason to change most existing uses of
    ACCESS_ONCE(), as these aren't currently harmful.
    
    However, for some features it is necessary to instrument reads and
    writes separately, which is not possible with ACCESS_ONCE(). This
    distinction is critical to correct operation.
    
    The bulk of the kernel code can be transformed via Coccinelle to use
    {READ,WRITE}_ONCE(), though this only modifies users of ACCESS_ONCE(),
    and not the implementation itself. As such, it has the potential to
    break homebrew ACCESS_ONCE() macros seen in some user code in the kernel
    tree (e.g. the virtio code, as fixed in commit ea9156fb).
    
    To avoid fragility if/when that transformation occurs, and to align with
    the preferred usage of {READ,WRITE}_ONCE(), this patch updates the DSCR
    selftest code to use READ_ONCE() rather than ACCESS_ONCE(). There should
    be no functional change as a result of this patch.
    Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Acked-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Shuah Khan <shuah@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: davem@davemloft.net
    Cc: linux-arch@vger.kernel.org
    Cc: snitzer@redhat.com
    Cc: thor.thayer@linux.intel.com
    Cc: tj@kernel.org
    Cc: viro@zeniv.linux.org.uk
    Cc: will.deacon@arm.com
    Link: http://lkml.kernel.org/r/1508792849-3115-11-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    564cbc87
dscr_default_test.c 2.66 KB