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Tighten rules for ACCESS_ONCE 

This series tightens the rules for ACCESS_ONCE to only work
 on scalar types. It also contains the necessary fixups as
 indicated by build bots of linux-next.
 Now everything is in place to prevent new non-scalar users
 of ACCESS_ONCE and we can continue to convert code to
 READ_ONCE/WRITE_ONCE.
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Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux

Pull ACCESS_ONCE() rule tightening from Christian Borntraeger:
 "Tighten rules for ACCESS_ONCE

  This series tightens the rules for ACCESS_ONCE to only work on scalar
  types.  It also contains the necessary fixups as indicated by build
  bots of linux-next.  Now everything is in place to prevent new
  non-scalar users of ACCESS_ONCE and we can continue to convert code to
  READ_ONCE/WRITE_ONCE"

* tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux:
  kernel: Fix sparse warning for ACCESS_ONCE
  next: sh: Fix compile error
  kernel: tighten rules for ACCESS ONCE
  mm/gup: Replace ACCESS_ONCE with READ_ONCE
  x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE
  x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE
  ppc/hugetlbfs: Replace ACCESS_ONCE with READ_ONCE
  ppc/kvm: Replace ACCESS_ONCE with READ_ONCE
This commit is contained in:
Linus Torvalds 2015-02-14 10:54:28 -08:00
parent fee5429e02 c5b19946eb
commit c833e17e27
8 changed files with 35 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
arch/powerpc/kvm/book3s_hv_rm_xics.c
View File

@ -152,7 +152,7 @@ static void icp_rm_down_cppr(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
* in virtual mode.
*/
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
/* Down_CPPR */
new_state.cppr = new_cppr;
@ -211,7 +211,7 @@ unsigned long kvmppc_rm_h_xirr(struct kvm_vcpu *vcpu)
* pending priority
*/
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
xirr = old_state.xisr | (((u32)old_state.cppr) << 24);
if (!old_state.xisr)
@ -277,7 +277,7 @@ int kvmppc_rm_h_ipi(struct kvm_vcpu *vcpu, unsigned long server,
* whenever the MFRR is made less favored.
*/
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
/* Set_MFRR */
new_state.mfrr = mfrr;
@ -352,7 +352,7 @@ int kvmppc_rm_h_cppr(struct kvm_vcpu *vcpu, unsigned long cppr)
icp_rm_clr_vcpu_irq(icp->vcpu);
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
reject = 0;
new_state.cppr = cppr;

16
arch/powerpc/kvm/book3s_xics.c
View File

@ -327,7 +327,7 @@ static bool icp_try_to_deliver(struct kvmppc_icp *icp, u32 irq, u8 priority,
icp->server_num);
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
*reject = 0;
@ -512,7 +512,7 @@ static void icp_down_cppr(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
* in virtual mode.
*/
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
/* Down_CPPR */
new_state.cppr = new_cppr;
@ -567,7 +567,7 @@ static noinline unsigned long kvmppc_h_xirr(struct kvm_vcpu *vcpu)
* pending priority
*/
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
xirr = old_state.xisr | (((u32)old_state.cppr) << 24);
if (!old_state.xisr)
@ -634,7 +634,7 @@ static noinline int kvmppc_h_ipi(struct kvm_vcpu *vcpu, unsigned long server,
* whenever the MFRR is made less favored.
*/
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
/* Set_MFRR */
new_state.mfrr = mfrr;
@ -679,7 +679,7 @@ static int kvmppc_h_ipoll(struct kvm_vcpu *vcpu, unsigned long server)
if (!icp)
return H_PARAMETER;
}
state = ACCESS_ONCE(icp->state);
state = READ_ONCE(icp->state);
kvmppc_set_gpr(vcpu, 4, ((u32)state.cppr << 24) | state.xisr);
kvmppc_set_gpr(vcpu, 5, state.mfrr);
return H_SUCCESS;
@ -721,7 +721,7 @@ static noinline void kvmppc_h_cppr(struct kvm_vcpu *vcpu, unsigned long cppr)
BOOK3S_INTERRUPT_EXTERNAL_LEVEL);
do {
old_state = new_state = ACCESS_ONCE(icp->state);
old_state = new_state = READ_ONCE(icp->state);
reject = 0;
new_state.cppr = cppr;
@ -885,7 +885,7 @@ static int xics_debug_show(struct seq_file *m, void *private)
if (!icp)
continue;
state.raw = ACCESS_ONCE(icp->state.raw);
state.raw = READ_ONCE(icp->state.raw);
seq_printf(m, "cpu server %#lx XIRR:%#x PPRI:%#x CPPR:%#x MFRR:%#x OUT:%d NR:%d\n",
icp->server_num, state.xisr,
state.pending_pri, state.cppr, state.mfrr,
@ -1082,7 +1082,7 @@ int kvmppc_xics_set_icp(struct kvm_vcpu *vcpu, u64 icpval)
* the ICS states before the ICP states.
*/
do {
old_state = ACCESS_ONCE(icp->state);
old_state = READ_ONCE(icp->state);
if (new_state.mfrr <= old_state.mfrr) {
resend = false;

4
arch/powerpc/mm/hugetlbpage.c
View File

@ -986,7 +986,7 @@ pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, unsigned *shift
*/
pdshift = PUD_SHIFT;
pudp = pud_offset(&pgd, ea);
pud = ACCESS_ONCE(*pudp);
pud = READ_ONCE(*pudp);
if (pud_none(pud))
return NULL;
@ -998,7 +998,7 @@ pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, unsigned *shift
else {
pdshift = PMD_SHIFT;
pmdp = pmd_offset(&pud, ea);
pmd = ACCESS_ONCE(*pmdp);
pmd = READ_ONCE(*pmdp);
/*
* A hugepage collapse is captured by pmd_none, because
* it mark the pmd none and do a hpte invalidate.

2
arch/sh/mm/gup.c
View File

@ -17,7 +17,7 @@
static inline pte_t gup_get_pte(pte_t *ptep)
{
#ifndef CONFIG_X2TLB
return ACCESS_ONCE(*ptep);
return READ_ONCE(*ptep);
#else
/*
* With get_user_pages_fast, we walk down the pagetables without

4
arch/x86/include/asm/spinlock.h
View File

@ -183,10 +183,10 @@ static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
__ticket_t head = ACCESS_ONCE(lock->tickets.head);
__ticket_t head = READ_ONCE(lock->tickets.head);
for (;;) {
struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
struct __raw_tickets tmp = READ_ONCE(lock->tickets);
/*
* We need to check "unlocked" in a loop, tmp.head == head
* can be false positive because of overflow.

2
arch/x86/xen/p2m.c
View File

@ -550,7 +550,7 @@ static bool alloc_p2m(unsigned long pfn)
mid_mfn = NULL;
}
p2m_pfn = pte_pfn(ACCESS_ONCE(*ptep));
p2m_pfn = pte_pfn(READ_ONCE(*ptep));
if (p2m_pfn == PFN_DOWN(__pa(p2m_identity)) ||
p2m_pfn == PFN_DOWN(__pa(p2m_missing))) {
/* p2m leaf page is missing */

21
include/linux/compiler.h
View File

@ -451,12 +451,23 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
* to make the compiler aware of ordering is to put the two invocations of
* ACCESS_ONCE() in different C statements.
*
* This macro does absolutely -nothing- to prevent the CPU from reordering,
* merging, or refetching absolutely anything at any time. Its main intended
* use is to mediate communication between process-level code and irq/NMI
* handlers, all running on the same CPU.
* ACCESS_ONCE will only work on scalar types. For union types, ACCESS_ONCE
* on a union member will work as long as the size of the member matches the
* size of the union and the size is smaller than word size.
*
* The major use cases of ACCESS_ONCE used to be (1) Mediating communication
* between process-level code and irq/NMI handlers, all running on the same CPU,
* and (2) Ensuring that the compiler does not fold, spindle, or otherwise
* mutilate accesses that either do not require ordering or that interact
* with an explicit memory barrier or atomic instruction that provides the
* required ordering.
*
* If possible use READ_ONCE/ASSIGN_ONCE instead.
*/
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
#define __ACCESS_ONCE(x) ({ \
__maybe_unused typeof(x) __var = (__force typeof(x)) 0; \
(volatile typeof(x) *)&(x); })
#define ACCESS_ONCE(x) (*__ACCESS_ONCE(x))
/* Ignore/forbid kprobes attach on very low level functions marked by this attribute: */
#ifdef CONFIG_KPROBES

2
mm/gup.c
View File

@ -1092,7 +1092,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
pmdp = pmd_offset(&pud, addr);
do {
pmd_t pmd = ACCESS_ONCE(*pmdp);
pmd_t pmd = READ_ONCE(*pmdp);
next = pmd_addr_end(addr, end);
if (pmd_none(pmd) || pmd_trans_splitting(pmd))