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locking/atomics, samples/mic/mpssd/mpssd.c: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE()

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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 ea9156fb3b).

To avoid fragility if/when that transformation occurs, and to align with
the preferred usage of {READ,WRITE}_ONCE(), this patch updates the MPSSD
sample code to use READ_ONCE() rather than ACCESS_ONCE(). There should
be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.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: mpe@ellerman.id.au
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/1508792849-3115-10-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Mark Rutland 2017-10-23 14:07:20 -07:00 committed by Ingo Molnar
parent ef4d9af62f
commit 94bbc9c1a0
1 changed files with 3 additions and 3 deletions
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6
samples/mic/mpssd/mpssd.c
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@ -65,7 +65,7 @@ static struct mic_info mic_list;
/* to align the pointer to the (next) page boundary */
#define PAGE_ALIGN(addr) _ALIGN(addr, PAGE_SIZE)
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
#define READ_ONCE(x) (*(volatile typeof(x) *)&(x))
#define GSO_ENABLED 1
#define MAX_GSO_SIZE (64 * 1024)
@ -382,7 +382,7 @@ disp_iovec(struct mic_info *mic, struct mic_copy_desc *copy,
static inline __u16 read_avail_idx(struct mic_vring *vr)
{
return ACCESS_ONCE(vr->info->avail_idx);
return READ_ONCE(vr->info->avail_idx);
}
static inline void txrx_prepare(int type, bool tx, struct mic_vring *vr,
@ -523,7 +523,7 @@ spin_for_descriptors(struct mic_info *mic, struct mic_vring *vr)
{
__u16 avail_idx = read_avail_idx(vr);
while (avail_idx == le16toh(ACCESS_ONCE(vr->vr.avail->idx))) {
while (avail_idx == le16toh(READ_ONCE(vr->vr.avail->idx))) {
#ifdef DEBUG
mpsslog("%s %s waiting for desc avail %d info_avail %d\n",
mic->name, __func__,